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Early in 1814, reviewing Biot's work on chromatic polarization, Young noted that the periodicity of the color as a function of the plate thickness—including the factor by which the period exceeded that for a reflective thin plate, and even the effect of obliquity of the plate (but not the role of polarization)—could be explained by the wave theory in terms of the different propagation times of the ordinary and extraordinary waves through the plate. But Young was then the only public defender of the wave theory.
In summary, in the spring of 1814, as Fresnel tried in vain to guess what polarization was, the corpuscularists thought that they knew, while the wave-theorists (if we may use the plural) literally had no idea. Both theories claimed to explain rectilinear propagation, but the wave explanation was overwhelmingly regarded as unconvincing. The corpuscular theory could not rigorously link double refraction to surface forces; the wave theory could not yet link it to polarization. The corpuscular theory was weak on thin plates and silent on gratings; the wave theory was strong on both, but under-appreciated. Concerning diffraction, the corpuscular theory did not yield quantitative predictions, while the wave theory had begun to do so by considering diffraction as a manifestation of interference, but had only considered two rays at a time. Only the corpuscular theory gave even a vague insight into Brewster's angle, Malus's law, or optical rotation. Concerning chromatic polarization, the wave theory explained the periodicity far better than the corpuscular theory, but had nothing to say about the role of polarization; and its explanation of the periodicity was largely ignored. And Arago had founded the study of chromatic polarization, only to lose the lead, controversially, to Biot. Such were the circumstances in which Arago first heard of Fresnel's interest in optics.
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Rêveries.
Fresnel's letters from later in 1814 reveal his interest in the wave theory, including his awareness that it explained the constancy of the speed of light and was at least compatible with stellar aberration. Eventually he compiled what he called his "rêveries" (musings) into an essay and submitted it via Léonor Mérimée to André-Marie Ampère, who did not respond directly. But on 19 December, Mérimée dined with Ampère and Arago, with whom he was acquainted through the École Polytechnique; and Arago promised to look at Fresnel's essay.
In mid 1815, on his way home to Mathieu to serve his suspension, Fresnel met Arago in Paris and spoke of the wave theory and stellar aberration. He was informed that he was trying to break down open doors ("il enfonçait des portes ouvertes"), and directed to classical works on optics.
Diffraction.
First attempt (1815).
On 12 July 1815, as Fresnel was about to leave Paris, Arago left him a note on a new topic:
Fresnel would not have ready access to these works outside Paris, and could not read English. But, in Mathieu—with a point-source of light made by focusing sunlight with a drop of honey, a crude micrometer of his own construction, and supporting apparatus made by a local locksmith—he began his own experiments. His technique was novel: whereas earlier investigators had projected the fringes onto a screen, Fresnel soon abandoned the screen and observed the fringes in space, through a lens with the micrometer at its focus, allowing more accurate measurements while requiring less light.
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Later in July, after Napoleon's final defeat, Fresnel was reinstated with the advantage of having backed the winning side. He requested a two-month leave of absence, which was readily granted because roadworks were in abeyance.
On 23 September he wrote to Arago, beginning "I think I have found the explanation and the law of colored fringes which one notices in the shadows of bodies illuminated by a luminous point." In the same paragraph, however, Fresnel implicitly acknowledged doubt about the novelty of his work: noting that he would need to incur some expense in order to improve his measurements, he wanted to know "whether this is not useless, and whether the law of diffraction has not already been established by sufficiently exact experiments." He explained that he had not yet had a chance to acquire the items on his reading lists, with the apparent exception of "Young's book", which he could not understand without his brother's help. Not surprisingly, he had retraced many of Young's steps.
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On 10 November, Fresnel sent a supplementary note dealing with Newton's rings and with gratings, including, for the first time, "transmission" gratings—although in that case the interfering rays were still assumed to be "inflected", and the experimental verification was inadequate because it used only two threads.
As Fresnel was not a member of the institute, the fate of his memoir depended heavily on the report of a single member. The reporter for Fresnel's memoir turned out to be Arago (with Poinsot as the other reviewer). On 8 November, Arago wrote to Fresnel:
Fresnel was troubled, wanting to know more precisely where he had collided with Young. Concerning the curved paths of the "colored bands", Young had noted the hyperbolic paths of the fringes in the two-source interference pattern, corresponding roughly to Fresnel's "internal" fringes, and had described the hyperbolic fringes that appear "on the screen" within rectangular shadows. He had not mentioned the curved paths of the "external" fringes of a shadow; but, as he later explained, that was because Newton had already done so. Newton evidently thought the fringes were "caustics". Thus Arago erred in his belief that the curved paths of the fringes were fundamentally incompatible with the corpuscular theory.
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Arago's letter went on to request more data on the external fringes. Fresnel complied, until he exhausted his leave and was assigned to Rennes in the département of Ille-et-Vilaine. At this point Arago interceded with Gaspard de Prony, head of the École des Ponts, who wrote to Louis-Mathieu Molé, head of the Corps des Ponts, suggesting that the progress of science and the prestige of the Corps would be enhanced if Fresnel could come to Paris for a time. He arrived in March 1816, and his leave was subsequently extended through the middle of the year.
Meanwhile, in an experiment reported on 26 February 1816, Arago verified Fresnel's prediction that the internal fringes were shifted if the rays on one side of the obstacle passed through a thin glass lamina. Fresnel correctly attributed this phenomenon to the lower wave velocity in the glass. Arago later used a similar argument to explain the colors in the scintillation of stars.
Fresnel's updated memoir was eventually published in the March 1816 issue of "Annales de Chimie et de Physique", of which Arago had recently become co-editor. That issue did not actually appear until May. In March, Fresnel already had competition: Biot read a memoir on diffraction by himself and his student Claude Pouillet, containing copious data and arguing that the regularity of diffraction fringes, like the regularity of Newton's rings, must be linked to Newton's "fits". But the new link was not rigorous, and Pouillet himself would become a distinguished early adopter of the wave theory.
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"Efficacious ray", double-mirror experiment (1816).
On 24 May 1816, Fresnel wrote to Young (in French), acknowledging how little of his own memoir was new. But in a "supplement" signed on 14 July and read the next day, Fresnel noted that the internal fringes were more accurately predicted by supposing that the two interfering rays came from some distance "outside" the edges of the obstacle. To explain this, he divided the incident wavefront at the obstacle into what we now call "Fresnel zones", such that the secondary waves from each zone were spread over half a cycle when they arrived at the observation point. The zones on one side of the obstacle largely canceled out in pairs, except the first zone, which was represented by an "efficacious ray". This approach worked for the internal fringes, but the superposition of the efficacious ray and the direct ray did "not" work for the "external" fringes.
The contribution from the "efficacious ray" was thought to be only "partly" canceled, for reasons involving the dynamics of the medium: where the wavefront was continuous, symmetry forbade oblique vibrations; but near the obstacle that truncated the wavefront, the asymmetry allowed some sideways vibration towards the geometric shadow. This argument showed that Fresnel had not (yet) fully accepted Huygens's principle, which would have permitted oblique radiation from all portions of the front.
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In the same supplement, Fresnel described his well-known double mirror, comprising two flat mirrors joined at an angle of slightly less than 180°, with which he produced a two-slit interference pattern from two virtual images of the same slit. A conventional double-slit experiment required a preliminary "single" slit to ensure that the light falling on the double slit was "coherent" (synchronized). In Fresnel's version, the preliminary single slit was retained, and the double slit was replaced by the double mirror—which bore no physical resemblance to the double slit and yet performed the same function. This result (which had been announced by Arago in the March issue of the "Annales") made it hard to believe that the two-slit pattern had anything to do with corpuscles being deflected as they passed near the edges of the slits.
But 1816 was the "Year Without a Summer": crops failed; hungry farming families lined the streets of Rennes; the central government organized "charity workhouses" for the needy; and in October, Fresnel was sent back to Ille-et-Vilaine to supervise charity workers in addition to his regular road crew. According to Arago,
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Fresnel's letters from December 1816 reveal his consequent anxiety. To Arago he complained of being "tormented by the worries of surveillance, and the need to reprimand…" And to Mérimée he wrote: "I find nothing more tiresome than having to manage other men, and I admit that I have no idea what I'm doing."
Prize memoir (1818) and sequel.
On 17 March 1817, the Académie des Sciences announced that diffraction would be the topic for the biannual physics "Grand Prix" to be awarded in 1819. The deadline for entries was set at 1 August 1818 to allow time for replication of experiments. Although the wording of the problem referred to rays and inflection and did not invite wave-based solutions, Arago and Ampère encouraged Fresnel to enter.
In the fall of 1817, Fresnel, supported by de Prony, obtained a leave of absence from the new head of the Corp des Ponts, Louis Becquey, and returned to Paris. He resumed his engineering duties in the spring of 1818; but from then on he was based in Paris, first on the Canal de l'Ourcq, and then (from May 1819) with the cadastre of the pavements.
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On 15 January 1818, in a different context (revisited below), Fresnel showed that the addition of sinusoidal functions of the same frequency but different phases is analogous to the addition of forces with different directions. His method was similar to the phasor representation, except that the "forces" were plane vectors rather than complex numbers; they could be added, and multiplied by scalars, but not (yet) multiplied and divided by each other. The explanation was algebraic rather than geometric.
Knowledge of this method was assumed in a preliminary note on diffraction, dated 19 April 1818 and deposited on 20 April, in which Fresnel outlined the elementary theory of diffraction as found in modern textbooks. He restated Huygens's principle in combination with the superposition principle, saying that the vibration at each point on a wavefront is the sum of the vibrations that would be sent to it at that moment by all the elements of the wavefront in any of its previous positions, all elements acting separately . For a wavefront partly obstructed in a previous position, the summation was to be carried out over the unobstructed portion. In directions other than the normal to the primary wavefront, the secondary waves were weakened due to obliquity, but weakened much more by destructive interference, so that the effect of obliquity alone could be ignored. For diffraction by a straight edge, the intensity as a function of distance from the geometric shadow could then be expressed with sufficient accuracy in terms of what are now called the normalized Fresnel integrals:
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The same note included a table of the integrals, for an upper limit ranging from 0 to 5.1 in steps of 0.1, computed with a mean error of 0.0003, plus a smaller table of maxima and minima of the resulting intensity.
In his final "Memoir on the diffraction of light", deposited on 29 July and bearing the Latin epigraph "Natura simplex et fecunda" ("Nature simple and fertile"), Fresnel slightly expanded the two tables without changing the existing figures, except for a correction to the first minimum of intensity. For completeness, he repeated his solution to "the problem of interference", whereby sinusoidal functions are added like vectors. He acknowledged the directionality of the secondary sources and the variation in their distances from the observation point, chiefly to explain why these things make negligible difference in the context, provided of course that the secondary sources do not radiate in the retrograde direction. Then, applying his theory of interference to the secondary waves, he expressed the intensity of light diffracted by a single straight edge (half-plane) in terms of integrals which involved the dimensions of the problem, but which could be converted to the normalized forms above. With reference to the integrals, he explained the calculation of the maxima and minima of the intensity (external fringes), and noted that the calculated intensity falls very rapidly as one moves into the geometric shadow. The last result, as Olivier Darrigol says, "amounts to a proof of the rectilinear propagation of light in the wave theory, indeed the first proof that a modern physicist would still accept."
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For the experimental testing of his calculations, Fresnel used red light with a wavelength of 638nm, which he deduced from the diffraction pattern in the simple case in which light incident on a single slit was focused by a cylindrical lens. For a variety of distances from the source to the obstacle and from the obstacle to the field point, he compared the calculated and observed positions of the fringes for diffraction by a half-plane, a slit, and a narrow strip—concentrating on the minima, which were visually sharper than the maxima. For the slit and the strip, he could not use the previously computed table of maxima and minima; for each combination of dimensions, the intensity had to be expressed in terms of sums or differences of Fresnel integrals and calculated from the table of integrals, and the extrema had to be calculated anew. The agreement between calculation and measurement was better than 1.5% in almost every case.
Near the end of the memoir, Fresnel summed up the difference between Huygens's use of secondary waves and his own: whereas Huygens says there is light only where the secondary waves exactly agree, Fresnel says there is complete darkness only where the secondary waves exactly cancel out.
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The judging committee comprised Laplace, Biot, and Poisson (all corpuscularists), Gay-Lussac (uncommitted), and Arago, who eventually wrote the committee's report. Although entries in the competition were supposed to be anonymous to the judges, Fresnel's must have been recognizable by the content. There was only one other entry, of which neither the manuscript nor any record of the author has survived. That entry (identified as "no.1") was mentioned only in the last paragraph of the judges' report, noting that the author had shown ignorance of the relevant earlier works of Young and Fresnel, used insufficiently precise methods of observation, overlooked known phenomena, and made obvious errors. In the words of John Worrall, "The competition facing Fresnel could hardly have been less stiff." We may infer that the committee had only two options: award the prize to Fresnel ("no. 2"), or withhold it.
The committee deliberated into the new year. Then Poisson, exploiting a case in which Fresnel's theory gave easy integrals, predicted that if a circular obstacle were illuminated by a point-source, there should be (according to the theory) a bright spot in the center of the shadow, illuminated as brightly as the exterior. This seems to have been intended as a "reductio ad absurdum". Arago, undeterred, assembled an experiment with an obstacle 2mm in diameter—and there, in the center of the shadow, was Poisson's spot.
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The unanimous report of the committee, read at the meeting of the Académie on 15 March 1819, awarded the prize to "the memoir marked no. 2, and bearing as epigraph: "Natura simplex et fecunda"." At the same meeting, after the judgment was delivered, the president of the Académie opened a sealed note accompanying the memoir, revealing the author as Fresnel. The award was announced at the public meeting of the Académie a week later, on 22 March.
Arago's verification of Poisson's counter-intuitive prediction passed into folklore as if it had decided the prize. That view, however, is not supported by the judges' report, which gave the matter only two sentences in the penultimate paragraph. Neither did Fresnel's triumph immediately convert Laplace, Biot, and Poisson to the wave theory, for at least four reasons. First, although the professionalization of science in France had established common standards, it was one thing to acknowledge a piece of research as meeting those standards, and another thing to regard it as conclusive. Second, it was possible to interpret Fresnel's integrals as rules for combining "rays". Arago even encouraged that interpretation, presumably in order to minimize resistance to Fresnel's ideas. Even Biot began teaching the Huygens-Fresnel principle without committing himself to a wave basis. Third, Fresnel's theory did not adequately explain the mechanism of generation of secondary waves or why they had any significant angular spread; this issue particularly bothered Poisson. Fourth, the question that most exercised optical physicists at that time was not diffraction, but polarization—on which Fresnel had been working, but was yet to make his critical breakthrough.
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Polarization.
Background: Emissionism and selectionism.
An "emission" theory of light was one that regarded the propagation of light as the transport of some kind of matter. While the corpuscular theory was obviously an emission theory, the converse did not follow: in principle, one could be an emissionist without being a corpuscularist. This was convenient because, beyond the ordinary laws of reflection and refraction, emissionists never managed to make testable quantitative predictions from a theory of forces acting on corpuscles of light. But they "did" make quantitative predictions from the premises that rays were countable objects, which were conserved in their interactions with matter (except absorbent media), and which had particular orientations with respect to their directions of propagation. According to this framework, polarization and the related phenomena of double refraction and partial reflection involved altering the orientations of the rays and/or selecting them according to orientation, and the state of polarization of a beam (a bundle of rays) was a question of how many rays were in what orientations: in a fully polarized beam, the orientations were all the same. This approach, which Jed Buchwald has called "selectionism", was pioneered by Malus and diligently pursued by Biot.
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Fresnel, in contrast, decided to introduce polarization into interference experiments.
Interference of polarized light, chromatic polarization (1816–21).
In July or August 1816, Fresnel discovered that when a birefringent crystal produced two images of a single slit, he could "not" obtain the usual two-slit interference pattern, even if he compensated for the different propagation times. A more general experiment, suggested by Arago, found that if the two beams of a double-slit device were separately polarized, the interference pattern appeared and disappeared as the polarization of one beam was rotated, giving full interference for parallel polarizations, but no interference for perpendicular polarizations . These experiments, among others, were eventually reported in a brief memoir published in 1819 and later translated into English.
In a memoir drafted on 30 August 1816 and revised on 6 October, Fresnel reported an experiment in which he placed two matching thin laminae in a double-slit apparatus—one over each slit, with their optic axes perpendicular—and obtained two interference patterns offset in opposite directions, with perpendicular polarizations. This, in combination with the previous findings, meant that each lamina split the incident light into perpendicularly polarized components with different velocities—just like a normal (thick) birefringent crystal, and contrary to Biot's "mobile polarization" hypothesis.
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Accordingly, in the same memoir, Fresnel offered his first attempt at a wave theory of chromatic polarization. When polarized light passed through a crystal lamina, it was split into ordinary and extraordinary waves (with intensities described by Malus's law), and these were perpendicularly polarized and therefore did not interfere, so that no colors were produced (yet). But if they then passed through an "analyzer" (second polarizer), their polarizations were brought into alignment (with intensities again modified according to Malus's law), and they would interfere. This explanation, by itself, predicts that if the analyzer is rotated 90°, the ordinary and extraordinary waves simply switch roles, so that if the analyzer takes the form of a calcite crystal, the two images of the lamina should be of the same hue (this issue is revisited below). But in fact, as Arago and Biot had found, they are of complementary colors. To correct the prediction, Fresnel proposed a phase-inversion rule whereby "one" of the constituent waves of "one" of the two images suffered an additional 180° phase shift on its way through the lamina. This inversion was a weakness in the theory relative to Biot's, as Fresnel acknowledged, although the rule specified which of the two images had the inverted wave. Moreover, Fresnel could deal only with special cases, because he had not yet solved the problem of superposing sinusoidal functions with arbitrary phase differences due to propagation at different velocities through the lamina.
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He solved that problem in a "supplement" signed on 15 January 1818 (mentioned above). In the same document, he accommodated Malus's law by proposing an underlying law: that if polarized light is incident on a birefringent crystal with its optic axis at an angle "θ" to the "plane of polarization", the ordinary and extraordinary vibrations (as functions of time) are scaled by the factors cos"θ" and sin"θ", respectively. Although modern readers easily interpret these factors in terms of perpendicular components of a "transverse" oscillation, Fresnel did not (yet) explain them that way. Hence he still needed the phase-inversion rule. He applied all these principles to a case of chromatic polarization not covered by Biot's formulae, involving "two" successive laminae with axes separated by 45°, and obtained predictions that disagreed with Biot's experiments (except in special cases) but agreed with his own.
Fresnel applied the same principles to the standard case of chromatic polarization, in which "one" birefringent lamina was sliced parallel to its axis and placed between a polarizer and an analyzer. If the analyzer took the form of a thick calcite crystal with its axis in the plane of polarization, Fresnel predicted that the intensities of the ordinary and extraordinary images of the lamina were respectively proportional to
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where formula_5 is the angle from the initial plane of polarization to the optic axis of the lamina, formula_6 is the angle from the initial plane of polarization to the plane of polarization of the final ordinary image, and formula_7 is the phase lag of the extraordinary wave relative to the ordinary wave due to the difference in propagation times through the lamina. The terms in formula_7 are the frequency-dependent terms and explain why the lamina must be "thin" in order to produce discernible colors: if the lamina is too thick, formula_9 will pass through too many cycles as the frequency varies through the visible range, and the eye (which divides the visible spectrum into only three bands) will not be able to resolve the cycles.
From these equations it is easily verified that formula_10 for all formula_11 so that the colors are complementary. Without the phase-inversion rule, there would be a "plus" sign in front of the last term in the second equation, so that the formula_7-dependent term would be the same in both equations, implying (incorrectly) that the colors were of the same hue.
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These equations were included in an undated note that Fresnel gave to Biot, to which Biot added a few lines of his own. If we substitute
then Fresnel's formulae can be rewritten as
which are none other than Biot's empirical formulae of 1812, except that Biot interpreted formula_17 and formula_18 as the "unaffected" and "affected" selections of the rays incident on the lamina. If Biot's substitutions were accurate, they would imply that his experimental results were more fully explained by Fresnel's theory than by his own.
Arago delayed reporting on Fresnel's works on chromatic polarization until June 1821, when he used them in a broad attack on Biot's theory. In his written response, Biot protested that Arago's attack went beyond the proper scope of a report on the nominated works of Fresnel. But Biot also claimed that the substitutions for formula_17 and formula_20 and therefore Fresnel's expressions for formula_21 and formula_22 were empirically wrong because when Fresnel's intensities of spectral colors were mixed according to Newton's rules, the squared cosine and sine functions varied too smoothly to account for the observed sequence of colors. That claim drew a written reply from Fresnel, who disputed whether the colors changed as abruptly as Biot claimed, and whether the human eye could judge color with sufficient objectivity for the purpose. On the latter question, Fresnel pointed out that different observers may give different names to the same color. Furthermore, he said, a single observer can only compare colors side by side; and even if they are judged to be the same, the identity is of sensation, not necessarily of composition. Fresnel's oldest and strongest point—that thin crystals were subject to the same laws as thick ones and did not need or allow a separate theory—Biot left unanswered. Arago and Fresnel were seen to have won the debate.
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Moreover, by this time Fresnel had a new, simpler explanation of his equations on chromatic polarization.
Breakthrough: Pure transverse waves (1821).
In the draft memoir of 30 August 1816, Fresnel mentioned two hypotheses—one of which he attributed to Ampère—by which the non-interference of orthogonally-polarized beams could be explained if polarized light waves were "partly" transverse. But Fresnel could not develop either of these ideas into a comprehensive theory. As early as September 1816, according to his later account, he realized that the non-interference of orthogonally-polarized beams, together with the phase-inversion rule in chromatic polarization, would be most easily explained if the waves were "purely" transverse, and Ampère "had the same thought" on the phase-inversion rule. But that would raise a new difficulty: as natural light seemed to be "un"polarized and its waves were therefore presumed to be longitudinal, one would need to explain how the longitudinal component of vibration disappeared on polarization, and why it did not reappear when polarized light was reflected or refracted obliquely by a glass plate.
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Independently, on 12 January 1817, Young wrote to Arago (in English) noting that a transverse vibration would constitute a polarization, and that if two longitudinal waves crossed at a significant angle, they could not cancel without leaving a residual transverse vibration. Young repeated this idea in an article published in a supplement to the "Encyclopædia Britannica" in February 1818, in which he added that Malus's law would be explained if polarization consisted in a transverse motion.
Thus Fresnel, by his own testimony, may not have been the first person to suspect that light waves could have a transverse "component", or that "polarized" waves were exclusively transverse. And it was Young, not Fresnel, who first "published" the idea that polarization depends on the orientation of a transverse vibration. But these incomplete theories had not reconciled the nature of polarization with the apparent existence of "unpolarized" light; that achievement was to be Fresnel's alone.
In a note that Buchwald dates in the summer of 1818, Fresnel entertained the idea that unpolarized waves could have vibrations of the same energy and obliquity, with their orientations distributed uniformly about the wave-normal, and that the degree of polarization was the degree of "non"-uniformity in the distribution. Two pages later he noted, apparently for the first time in writing, that his phase-inversion rule and the non-interference of orthogonally-polarized beams would be easily explained if the vibrations of fully polarized waves were "perpendicular to the normal to the wave"—that is, purely transverse.
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But if he could account for "lack" of polarization by averaging out the transverse component, he did not also need to assume a longitudinal component. It was enough to suppose that light waves are "purely" transverse, hence "always" polarized in the sense of having a particular transverse orientation, and that the "unpolarized" state of natural or "direct" light is due to rapid and random variations in that orientation, in which case two "coherent" portions of "unpolarized" light will still interfere because their orientations will be synchronized.
It is not known exactly when Fresnel made this last step, because there is no relevant documentation from 1820 or early 1821 (perhaps because he was too busy working on lighthouse-lens prototypes; see below). But he first "published" the idea in a paper on "Calcul des teintes…" ("calculation of the tints…"), serialized in Arago's "Annales" for May, June, and July 1821. In the first installment, Fresnel described "direct" (unpolarized) light as "the rapid succession of systems of waves polarized in all directions", and gave what is essentially the modern explanation of chromatic polarization, albeit in terms of the analogy between polarization and the resolution of forces in a plane, mentioning transverse waves only in a footnote. The introduction of transverse waves into the main argument was delayed to the second installment, in which he revealed the suspicion that he and Ampère had harbored since 1816, and the difficulty it raised. He continued:
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According to this new view, he wrote, "the act of polarization consists not in creating these transverse movements, but in decomposing them into two fixed perpendicular directions and in separating the two components".
While selectionists could insist on interpreting Fresnel's diffraction integrals in terms of discrete, countable rays, they could not do the same with his theory of polarization. For a selectionist, the state of polarization of a beam concerned the distribution of orientations over the "population" of rays, and that distribution was presumed to be static. For Fresnel, the state of polarization of a beam concerned the variation of a displacement over "time". That displacement might be constrained but was "not" static, and rays were geometric constructions, "not" countable objects. The conceptual gap between the wave theory and selectionism had become unbridgeable.
The other difficulty posed by pure transverse waves, of course, was the apparent implication that the aether was an elastic "solid", except that, unlike other elastic solids, it was incapable of transmitting longitudinal waves. The wave theory was cheap on assumptions, but its latest assumption was expensive on credulity. If that assumption was to be widely entertained, its explanatory power would need to be impressive.
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Partial reflection (1821).
In the second installment of "Calcul des teintes" (June 1821), Fresnel supposed, by analogy with sound waves, that the density of the aether in a refractive medium was inversely proportional to the square of the wave velocity, and therefore directly proportional to the square of the refractive index. For reflection and refraction at the surface between two isotropic media of different indices, Fresnel decomposed the transverse vibrations into two perpendicular components, now known as the "s" and "p" components, which are parallel to the "surface" and the "plane" of incidence, respectively; in other words, the "s" and "p" components are respectively "square" and "parallel" to the plane of incidence. For the "s" component, Fresnel supposed that the interaction between the two media was analogous to an elastic collision, and obtained a formula for what we now call the "reflectivity": the ratio of the reflected intensity to the incident intensity. The predicted reflectivity was non-zero at all angles.
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The third installment (July 1821) was a short "postscript" in which Fresnel announced that he had found, by a "mechanical solution", a formula for the reflectivity of the "p" component, which predicted that "the reflectivity was zero at the Brewster angle". So polarization by reflection had been accounted for—but with the proviso that the direction of vibration in Fresnel's model was "perpendicular" to the plane of polarization as defined by Malus. (On the ensuing controversy, see "Plane of polarization".) The technology of the time did not allow the "s" and "p" reflectivities to be measured accurately enough to test Fresnel's formulae at arbitrary angles of incidence. But the formulae could be rewritten in terms of what we now call the "reflection coefficient": the signed ratio of the reflected amplitude to the incident amplitude. Then, if the plane of polarization of the incident ray was at 45° to the plane of incidence, the tangent of the corresponding angle for the reflected ray was obtainable from the "ratio" of the two reflection coefficients, and this angle could be measured. Fresnel had measured it for a range of angles of incidence, for glass and water, and the agreement between the calculated and measured angles was better than 1.5° in all cases.
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Fresnel gave details of the "mechanical solution" in a memoir read to the Académie des Sciences on 7 January 1823. Conservation of energy was combined with continuity of the "tangential" vibration at the interface. The resulting formulae for the reflection coefficients and reflectivities became known as the "Fresnel equations". The reflection coefficients for the "s" and "p" polarizations are most succinctly expressed as
where formula_5 and formula_26 are the angles of incidence and refraction; these equations are known respectively as "Fresnel's sine law" and "Fresnel's tangent law". By allowing the coefficients to be "complex", Fresnel even accounted for the different phase shifts of the "s" and "p" components due to total internal reflection.
This success inspired James MacCullagh and Augustin-Louis Cauchy, beginning in 1836, to analyze reflection from metals by using the Fresnel equations with a complex refractive index. The same technique is applicable to non-metallic opaque media. With these generalizations, the Fresnel equations can predict the appearance of a wide variety of objects under illumination—for example, in computer graphics .
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Circular and elliptical polarization, optical rotation (1822).
In a memoir dated 9 December 1822, Fresnel coined the terms "linear polarization" (French: "polarisation rectiligne") for the simple case in which the perpendicular components of vibration are in phase or 180° out of phase, "circular polarization" for the case in which they are of equal magnitude and a quarter-cycle (±90°) out of phase, and "elliptical polarization" for other cases in which the two components have a fixed amplitude ratio and a fixed phase difference. He then explained how optical rotation could be understood as a species of birefringence. Linearly-polarized light could be resolved into two circularly-polarized components rotating in opposite directions. If these components propagated at slightly different speeds, the phase difference between them—and therefore the direction of their linearly-polarized resultant—would vary continuously with distance.
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Total internal reflection (1817–23).
By 1817 it had been discovered by Brewster, but not adequately reported, that plane-polarized light was partly depolarized by total internal reflection if initially polarized at an acute angle to the plane of incidence. Fresnel rediscovered this effect and investigated it by including total internal reflection in a chromatic-polarization experiment. With the aid of his "first" theory of chromatic polarization, he found that the apparently depolarized light was a mixture of components polarized parallel and perpendicular to the plane of incidence, and that the total reflection introduced a phase difference between them. Choosing an appropriate angle of incidence (not yet exactly specified) gave a phase difference of 1/8 of a cycle (45°). Two such reflections from the "parallel faces" of "two coupled prisms" gave a phase difference of 1/4 of a cycle (90°). These findings were contained in a memoir submitted to the Académie on 10 November 1817 and read a fortnight later. An undated marginal note indicates that the two coupled prisms were later replaced by a single "parallelepiped in glass"—now known as a "Fresnel rhomb".
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This was the memoir whose "supplement", dated January 1818, contained the method of superposing sinusoidal functions and the restatement of Malus's law in terms of amplitudes. In the same supplement, Fresnel reported his discovery that optical rotation could be emulated by passing the polarized light through a Fresnel rhomb (still in the form of "coupled prisms"), followed by an ordinary birefringent lamina sliced parallel to its axis, with the axis at 45° to the plane of reflection of the Fresnel rhomb, followed by a second Fresnel rhomb at 90° to the first. In a further memoir read on 30 March, Fresnel reported that if polarized light was fully "depolarized" by a Fresnel rhomb—now described as a parallelepiped—its properties were not further modified by a subsequent passage through an optically rotating medium or device.
The connection between optical rotation and birefringence was further explained in 1822, in the memoir on elliptical and circular polarization. This was followed by the memoir on reflection, read in January 1823, in which Fresnel quantified the phase shifts in total internal reflection, and thence calculated the precise angle at which a Fresnel rhomb should be cut in order to convert linear polarization to circular polarization. For a refractive index of 1.51, there were two solutions: about 48.6° and 54.6°.
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Double refraction.
Background: Uniaxial and biaxial crystals; Biot's laws.
When light passes through a slice of calcite cut perpendicular to its optic axis, the difference between the propagation times of the ordinary and extraordinary waves has a second-order dependence on the angle of incidence. If the slice is observed in a highly convergent cone of light, that dependence becomes significant, so that a chromatic-polarization experiment will show a pattern of concentric rings. But most minerals, when observed in this manner, show a more complicated pattern of rings involving two foci and a lemniscate curve, as if they had "two" optic axes. The two classes of minerals naturally become known as "uniaxal" and "biaxal"—or, in later literature, "uniaxial" and "biaxial".
In 1813, Brewster observed the simple concentric pattern in "beryl, emerald, ruby &c." The same pattern was later observed in calcite by Wollaston, Biot, and Seebeck. Biot, assuming that the concentric pattern was the general case, tried to calculate the colors with his theory of chromatic polarization, and succeeded better for some minerals than for others. In 1818, Brewster belatedly explained why: seven of the twelve minerals employed by Biot had the lemniscate pattern, which Brewster had observed as early as 1812; and the minerals with the more complicated rings also had a more complicated law of refraction.
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In a uniform crystal, according to Huygens's theory, the secondary wavefront that expands from the origin in unit time is the "ray-velocity surface"—that is, the surface whose "distance" from the origin in any direction is the ray velocity in that direction. In calcite, this surface is two-sheeted, consisting of a sphere (for the ordinary wave) and an oblate spheroid (for the extraordinary wave) touching each other at opposite points of a common axis—touching at the north and south poles, if we may use a geographic analogy. But according to Malus's "corpuscular" theory of double refraction, the ray velocity was proportional to the reciprocal of that given by Huygens's theory, in which case the velocity law was of the form
where formula_28 and formula_29 were the ordinary and extraordinary ray velocities "according to the corpuscular theory", and formula_30 was the angle between the ray and the optic axis. By Malus's definition, the plane of polarization of a ray was the plane of the ray and the optic axis if the ray was ordinary, or the perpendicular plane (containing the ray) if the ray was extraordinary. In Fresnel's model, the direction of vibration was normal to the plane of polarization. Hence, for the sphere (the ordinary wave), the vibration was along the lines of latitude (continuing the geographic analogy); and for the spheroid (the extraordinary wave), the vibration was along the lines of longitude.
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On 29 March 1819, Biot presented a memoir in which he proposed simple generalizations of Malus's rules for a crystal with "two" axes, and reported that both generalizations seemed to be confirmed by experiment. For the velocity law, the squared sine was replaced by the "product" of the sines of the angles from the ray to the two axes ("Biot's sine law"). And for the polarization of the ordinary ray, the plane of the ray and the axis was replaced by the plane bisecting the dihedral angle between the two planes each of which contained the ray and one axis ("Biot's dihedral law"). Biot's laws meant that a biaxial crystal with axes at a small angle, cleaved in the plane of those axes, behaved nearly like a uniaxial crystal at near-normal incidence; this was fortunate because gypsum, which had been used in chromatic-polarization experiments, is biaxial.
First memoir and supplements (1821–22).
Until Fresnel turned his attention to biaxial birefringence, it was assumed that one of the two refractions was ordinary, even in biaxial crystals. But, in a memoir submitted on 19 November 1821, Fresnel reported two experiments on topaz showing that "neither refraction" was ordinary in the sense of satisfying Snell's law; that is, neither ray was the product of spherical secondary waves.
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The same memoir contained Fresnel's first attempt at the biaxial velocity law. For calcite, if we interchange the equatorial and polar radii of Huygens's oblate spheroid while preserving the polar direction, we obtain a "prolate" spheroid touching the sphere at the equator. A plane through the center/origin cuts this prolate spheroid in an ellipse whose major and minor semi-axes give the magnitudes of the extraordinary and ordinary ray velocities in the direction normal to the plane, and (said Fresnel) the directions of their respective vibrations. The direction of the optic axis is the normal to the plane for which the ellipse of intersection reduces to a "circle". So, for the biaxial case, Fresnel simply replaced the prolate spheroid with a triaxial ellipsoid, which was to be sectioned by a plane in the same way. In general there would be "two" planes passing through the center of the ellipsoid and cutting it in a circle, and the normals to these planes would give "two" optic axes. From the geometry, Fresnel deduced Biot's sine law (with the ray velocities replaced by their reciprocals).
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The ellipsoid indeed gave the correct ray velocities (although the initial experimental verification was only approximate). But it did not give the correct directions of vibration, for the biaxial case or even for the uniaxial case, because the vibrations in Fresnel's model were tangential to the wavefront—which, for an extraordinary ray, is "not" generally normal to the ray. This error (which is small if, as in most cases, the birefringence is weak) was corrected in an "extract" that Fresnel read to the Académie a week later, on 26 November. Starting with Huygens's spheroid, Fresnel obtained a 4th-degree surface which, when sectioned by a plane as above, would yield the "wave-normal velocities" for a wavefront in that plane, together with their vibration directions. For the biaxial case, he generalized the equation to obtain a surface with three unequal principal dimensions; this he subsequently called the "surface of elasticity". But he retained the earlier ellipsoid as an approximation, from which he deduced Biot's dihedral law.
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Fresnel's initial derivation of the surface of elasticity had been purely geometric, and not deductively rigorous. His first attempt at a "mechanical" derivation, contained in a "supplement" dated 13 January 1822, assumed that (i) there were three mutually perpendicular directions in which a displacement produced a reaction in the same direction, (ii) the reaction was otherwise a linear function of the displacement, and (iii) the radius of the surface in any direction was the square root of the component, "in that direction", of the reaction to a unit displacement in that direction. The last assumption recognized the requirement that if a wave was to maintain a fixed direction of propagation and a fixed direction of vibration, the reaction must not be outside the plane of those two directions.
In the same supplement, Fresnel considered how he might find, for the biaxial case, the secondary wavefront that expands from the origin in unit time—that is, the surface that reduces to Huygens's sphere and spheroid in the uniaxial case. He noted that this "wave surface" ("surface de l'onde") is tangential to all possible plane wavefronts that could have crossed the origin one unit of time ago, and he listed the mathematical conditions that it must satisfy. But he doubted the feasibility of deriving the surface "from" those conditions.
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In a "second supplement", Fresnel eventually exploited two related facts: (i) the "wave surface" was also the ray-velocity surface, which could be obtained by sectioning the ellipsoid that he had initially mistaken for the surface of elasticity, and (ii) the "wave surface" intersected each plane of symmetry of the ellipsoid in two curves: a circle and an ellipse. Thus he found that the "wave surface" is described by the 4th-degree equation
where formula_32 and formula_33 are the propagation speeds in directions normal to the coordinate axes for vibrations along the axes (the ray and wave-normal speeds being the same in those special cases). Later commentators put the equation in the more compact and memorable form
Earlier in the "second supplement", Fresnel modeled the medium as an array of point-masses and found that the force-displacement relation was described by a symmetric matrix, confirming the existence of three mutually perpendicular axes on which the displacement produced a parallel force. Later in the document, he noted that in a biaxial crystal, unlike a uniaxial crystal, the directions in which there is only one wave-normal velocity are not the same as those in which there is only one ray velocity. Nowadays we refer to the former directions as the "optic" axes or "binormal" axes, and the latter as the "ray" axes or "biradial" axes .
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Fresnel's "second supplement" was signed on 31 March 1822 and submitted the next day—less than a year after the publication of his pure-transverse-wave hypothesis, and just less than a year after the demonstration of his prototype eight-panel lighthouse lens .
Second memoir (1822–26).
Having presented the pieces of his theory in roughly the order of discovery, Fresnel needed to rearrange the material so as to emphasize the mechanical foundations; and he still needed a rigorous treatment of Biot's dihedral law. He attended to these matters in his "second memoir" on double refraction, published in the "Recueils" of the Académie des Sciences for 1824; this was not actually printed until late 1827, a few months after his death. In this work, having established the three perpendicular axes on which a displacement produces a parallel reaction, and thence constructed the surface of elasticity, he showed that Biot's dihedral law is exact provided that the binormals are taken as the optic axes, and the wave-normal direction as the direction of propagation.
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As early as 1822, Fresnel discussed his perpendicular axes with Cauchy. Acknowledging Fresnel's influence, Cauchy went on to develop the first rigorous theory of elasticity of non-isotropic solids (1827), hence the first rigorous theory of transverse waves therein (1830)—which he promptly tried to apply to optics. The ensuing difficulties drove a long competitive effort to find an accurate mechanical model of the aether. Fresnel's own model was not dynamically rigorous; for example, it deduced the reaction to a shear strain by considering the displacement of one particle while all others were fixed, and it assumed that the stiffness determined the wave velocity as in a stretched string, whatever the direction of the wave-normal. But it was enough to enable the wave theory to do what selectionist theory could not: generate testable formulae covering a comprehensive range of optical phenomena, from "mechanical" assumptions.
Photoelasticity, multiple-prism experiments (1822).
In 1815, Brewster reported that colors appear when a slice of isotropic material, placed between crossed polarizers, is mechanically stressed. Brewster himself immediately and correctly attributed this phenomenon to stress-induced birefringence—now known as "photoelasticity".
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In a memoir read in September 1822, Fresnel announced that he had verified Brewster's diagnosis more directly, by compressing a combination of glass prisms so severely that one could actually see a double image through it. In his experiment, Fresnel lined up seven 45°–90°–45° prisms, short side to short side, with their 90° angles pointing in alternating directions. Two half-prisms were added at the ends to make the whole assembly rectangular. The prisms were separated by thin films of turpentine ("térébenthine") to suppress internal reflections, allowing a clear line of sight along the row. When the four prisms with similar orientations were compressed in a vise across the line of sight, an object viewed through the assembly produced two images with perpendicular polarizations, with an apparent spacing of 1.5mm at one metre.
At the end of that memoir, Fresnel predicted that if the compressed prisms were replaced by (unstressed) monocrystalline quartz prisms with matching directions of optical rotation, and with their optic axes aligned along the row, an object seen by looking along the common optic axis would give two images, which would seem unpolarized when viewed through an analyzer but, when viewed through a Fresnel rhomb, would be polarized at ±45° to the plane of reflection of the rhomb (indicating that they were initially circularly polarized in opposite directions). This would show directly that optical rotation is a form of birefringence. In the memoir of December 1822, in which he introduced the term "circular polarization", he reported that he had confirmed this prediction using only one 14°–152°–14° prism and two glass half-prisms. But he obtained a wider separation of the images by replacing the glass half-prism with quartz half-prisms whose rotation was opposite to that of the 14°–152°–14° prism. He added in passing that one could further increase the separation by increasing the number of prisms.
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Reception.
For the supplement to Riffault's translation of Thomson's "System of Chemistry", Fresnel was chosen to contribute the article on light. The resulting 137-page essay, titled "De la Lumière" ("On Light"), was apparently finished in June 1821 and published by February 1822. With sections covering the nature of light, diffraction, thin-film interference, reflection and refraction, double refraction and polarization, chromatic polarization, and modification of polarization by reflection, it made a comprehensive case for the wave theory to a readership that was not restricted to physicists.
To examine Fresnel's first memoir and supplements on double refraction, the Académie des Sciences appointed Ampère, Arago, Fourier, and Poisson. Their report, of which Arago was clearly the main author, was delivered at the meeting of 19 August 1822. Then, in the words of Émile Verdet, as translated by Ivor Grattan-Guinness:
Whether Laplace was announcing his conversion to the wave theory—at the age of 73—is uncertain. Grattan-Guinness entertained the idea. Buchwald, noting that Arago failed to explain that the "ellipsoid of elasticity" did not give the correct planes of polarization, suggests that Laplace may have merely regarded Fresnel's theory as a successful generalization of Malus's ray-velocity law, embracing Biot's laws.
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In the following year, Poisson, who did not sign Arago's report, disputed the possibility of transverse waves in the aether. Starting from assumed equations of motion of a fluid medium, he noted that they did not give the correct results for partial reflection and double refraction—as if that were Fresnel's problem rather than his own—and that the predicted waves, even if they were initially transverse, became more longitudinal as they propagated. In reply Fresnel noted, "inter alia", that the equations in which Poisson put so much faith did not even predict viscosity. The implication was clear: given that the behavior of light had not been satisfactorily explained except by transverse waves, it was not the responsibility of the wave-theorists to abandon transverse waves in deference to pre-conceived notions about the aether; rather, it was the responsibility of the aether modelers to produce a model that accommodated transverse waves. According to Robert H. Silliman, Poisson eventually accepted the wave theory shortly before his death in 1840.
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Among the French, Poisson's reluctance was an exception. According to Eugene Frankel, "in Paris no debate on the issue seems to have taken place after 1825. Indeed, almost the entire generation of physicists and mathematicians who came to maturity in the 1820s—Pouillet, Savart, Lamé, Navier, Liouville, Cauchy—seem to have adopted the theory immediately." Fresnel's other prominent French opponent, Biot, appeared to take a neutral position in 1830, and eventually accepted the wave theory—possibly by 1846 and certainly by 1858.
In 1826, the British astronomer John Herschel, who was working on a book-length article on light for the "Encyclopædia Metropolitana", addressed three questions to Fresnel concerning double refraction, partial reflection, and their relation to polarization. The resulting article, titled simply "Light", was highly sympathetic to the wave theory, although not entirely free of selectionist language. It was circulating privately by 1828 and was published in 1830. Meanwhile, Young's translation of Fresnel's "De la Lumière" was published in installments from 1827 to 1829. George Biddell Airy, the former Lucasian Professor at Cambridge and future Astronomer Royal, unreservedly accepted the wave theory by 1831. In 1834, he famously calculated the diffraction pattern of a circular aperture from the wave theory, thereby explaining the limited angular resolution of a perfect telescope . By the end of the 1830s, the only prominent British physicist who held out against the wave theory was Brewster, whose objections included the difficulty of explaining photochemical effects and (in his opinion) dispersion.
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A German translation of "De la Lumière" was published in installments in 1825 and 1828. The wave theory was adopted by Fraunhofer in the early 1820s and by Franz Ernst Neumann in the 1830s, and then began to find favor in German textbooks.
The economy of assumptions under the wave theory was emphasized by William Whewell in his "History of the Inductive Sciences", first published in 1837. In the corpuscular system, "every new class of facts requires a new supposition," whereas in the wave system, a hypothesis devised in order to explain one phenomenon is then found to explain or predict others. In the corpuscular system there is "no unexpected success, no happy coincidence, no convergence of principles from remote quarters"; but in the wave system, "all tends to unity and simplicity."
Hence, in 1850, when Foucault and Fizeau found by experiment that light travels more slowly in water than in air, in accordance with the wave explanation of refraction and contrary to the corpuscular explanation, the result came as no surprise.
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Lighthouses and the Fresnel lens.
Fresnel was not the first person to focus a lighthouse beam using a lens. That distinction apparently belongs to the London glass-cutter Thomas Rogers, whose first lenses, 53cm in diameter and 14cm thick at the center, were installed at the Old Lower Lighthouse at Portland Bill in 1789. Further samples were installed in about half a dozen other locations by 1804. But much of the light was wasted by absorption in the glass.
Nor was Fresnel the first to suggest replacing a convex lens with a series of concentric annular prisms, to reduce weight and absorption. In 1748, Count Buffon proposed grinding such prisms as steps in a single piece of glass. In 1790, the Marquis de Condorcet suggested that it would be easier to make the annular sections separately and assemble them on a frame; but even that was impractical at the time. These designs were intended not for lighthouses, but for burning glasses. Brewster, however, proposed a system similar to Condorcet's in 1811, and by 1820 was advocating its use in British lighthouses.
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Meanwhile, on 21 June 1819, Fresnel was "temporarily" seconded by the "Commission des Phares" (Commission of Lighthouses) on the recommendation of Arago (a member of the Commission since 1813), to review possible improvements in lighthouse illumination. The commission had been established by Napoleon in 1811 and placed under the Corps des Ponts—Fresnel's employer.
By the end of August 1819, unaware of the Buffon-Condorcet-Brewster proposal, Fresnel made his first presentation to the commission, recommending what he called "lentilles à échelons" (lenses by steps) to replace the reflectors then in use, which reflected only about half of the incident light. One of the assembled commissioners, Jacques Charles, recalled Buffon's suggestion, leaving Fresnel embarrassed for having again "broken through an open door". But, whereas Buffon's version was biconvex and in one piece, Fresnel's was plano-convex and made of multiple prisms for easier construction. With an official budget of 500 francs, Fresnel approached three manufacturers. The third, François Soleil, produced the prototype. Finished in March 1820, it had a square lens panel 55cm on a side, containing 97 polygonal (not annular) prisms—and so impressed the Commission that Fresnel was asked for a full eight-panel version. This model, completed a year later in spite of insufficient funding, had panels 76cm square. In a public spectacle on the evening of 13 April 1821, it was demonstrated by comparison with the most recent reflectors, which it suddenly rendered obsolete.
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Fresnel's next lens was a rotating apparatus with eight "bull's-eye" panels, made in annular arcs by Saint-Gobain, giving eight rotating beams—to be seen by mariners as a periodic flash. Above and behind each main panel was a smaller, sloping bull's-eye panel of trapezoidal outline with trapezoidal elements. This refracted the light to a sloping plane mirror, which then reflected it horizontally, 7 degrees ahead of the main beam, increasing the duration of the flash. Below the main panels were 128 small mirrors arranged in four rings, stacked like the slats of a louver or Venetian blind. Each ring, shaped as a frustum of a cone, reflected the light to the horizon, giving a fainter steady light between the flashes. The official test, conducted on the unfinished "Arc de Triomphe" on 20 August 1822, was witnessed by the commission—and by Louis XVIII and his entourage—from 32km away. The apparatus was stored at Bordeaux for the winter, and then reassembled at Cordouan Lighthouse under Fresnel's supervision. On 25 July 1823, the world's first lighthouse Fresnel lens was lit. Soon afterwards, Fresnel started coughing up blood.
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In May 1824, Fresnel was promoted to secretary of the "Commission des Phares", becoming the first member of that body to draw a salary, albeit in the concurrent role of Engineer-in-Chief. He was also an examiner (not a teacher) at the École Polytechnique since 1821; but poor health, long hours during the examination season, and anxiety about judging others induced him to resign that post in late 1824, to save his energy for his lighthouse work.
In the same year he designed the first "fixed" lens—for spreading light evenly around the horizon while minimizing waste above or below. Ideally the curved refracting surfaces would be segments of toroids about a common vertical axis, so that the dioptric panel would look like a cylindrical drum. If this was supplemented by reflecting (catoptric) rings above and below the refracting (dioptric) parts, the entire apparatus would look like a beehive. The second Fresnel lens to enter service was indeed a fixed lens, of third order, installed at Dunkirk by 1 February 1825. However, due to the difficulty of fabricating large toroidal prisms, this apparatus had a 16-sided polygonal plan.
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In 1825, Fresnel extended his fixed-lens design by adding a rotating array outside the fixed array. Each panel of the rotating array was to refract part of the fixed light from a horizontal fan into a narrow beam.
Also in 1825, Fresnel unveiled the "Carte des Phares" (Lighthouse Map), calling for a system of 51 lighthouses plus smaller harbor lights, in a hierarchy of lens sizes (called "orders", the first order being the largest), with different characteristics to facilitate recognition: a constant light (from a fixed lens), one flash per minute (from a rotating lens with eight panels), and two per minute (sixteen panels).
In late 1825, to reduce the loss of light in the reflecting elements, Fresnel proposed to replace each mirror with a catadioptric prism, through which the light would travel by refraction through the first surface, then total internal reflection off the second surface, then refraction through the third surface. The result was the lighthouse lens as we now know it. In 1826 he assembled a small model for use on the Canal Saint-Martin, but he did not live to see a full-sized version.
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The first fixed lens with toroidal prisms was a first-order apparatus designed by the Scottish engineer Alan Stevenson under the guidance of Léonor Fresnel, and fabricated by Isaac Cookson & Co. from French glass; it entered service at the Isle of May in 1836. The first large catadioptric lenses were fixed third-order lenses made in 1842 for the lighthouses at Gravelines and Île Vierge. The first fully catadioptric "first-order" lens, installed at Ailly in 1852, gave eight rotating beams assisted by eight catadioptric panels at the top (to lengthen the flashes), plus a fixed light from below. The first fully catadioptric lens with "purely revolving" beams—also of first order—was installed at Saint-Clément-des-Baleines in 1854, and marked the completion of Augustin Fresnel's original "Carte des Phares".
Production of one-piece stepped dioptric lenses—roughly as envisaged by Buffon—became practical in 1852, when John L. Gilliland of the Brooklyn Flint-Glass Company patented a method of making such lenses from press-molded glass. By the 1950s, the substitution of plastic for glass made it economic to use fine-stepped Fresnel lenses as condensers in overhead projectors. Still finer steps can be found in low-cost plastic "sheet" magnifiers.
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Honors.
Fresnel was elected to the "Société Philomathique de Paris" in April 1819, and in 1822 became one of the editors of the Société's "Bulletin des Sciences". As early as May 1817, at Arago's suggestion, Fresnel applied for membership of the Académie des Sciences, but received only one vote. The successful candidate on that occasion was Joseph Fourier. In November 1822, Fourier's elevation to Permanent Secretary of the Académie created a vacancy in the physics section, which was filled in February 1823 by Pierre Louis Dulong, with 36 votes to Fresnel's 20. But in May 1823, after another vacancy was left by the death of Jacques Charles, Fresnel's election was unanimous. In 1824, Fresnel was made a "chevalier de la Légion d'honneur" (Knight of the Legion of Honour).
Meanwhile, in Britain, the wave theory was yet to take hold; Fresnel wrote to Thomas Young in November 1824, saying in part:
But "the praise of English scholars" soon followed. On 9 June 1825, Fresnel was made a Foreign Member of the Royal Society of London. In 1827 he was awarded the society's Rumford Medal for the year 1824, "For his Development of the Undulatory Theory as applied to the Phenomena of Polarized Light, and for his various important discoveries in Physical Optics."
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A monument to Fresnel at his birthplace was dedicated on 14 September 1884 with a speech by , Permanent Secretary of the Académie des Sciences. "" is among the 72 names embossed on the Eiffel Tower (on the south-east side, fourth from the left). In the 19th century, as every lighthouse in France acquired a Fresnel lens, every one acquired a bust of Fresnel, seemingly watching over the coastline that he had made safer. The lunar features "Promontorium Fresnel" and "Rimae Fresnel" were later named after him.
Decline and death.
Fresnel's health, which had always been poor, deteriorated in the winter of 1822–1823, increasing the urgency of his original research, and (in part) preventing him from contributing an article on polarization and double refraction for the "Encyclopædia Britannica". The memoirs on circular and elliptical polarization and optical rotation, and on the detailed derivation of the Fresnel equations and their application to total internal reflection, date from this period. In the spring he recovered enough, in his own view, to supervise the lens installation at Cordouan. Soon afterwards, it became clear that his condition was tuberculosis.
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In 1824, he was advised that if he wanted to live longer, he needed to scale back his activities. Perceiving his lighthouse work to be his most important duty, he resigned as an examiner at the École Polytechnique, and closed his scientific notebooks. His last note to the Académie, read on 13 June 1825, described the first radiometer and attributed the observed repulsive force to a temperature difference. Although his fundamental research ceased, his advocacy did not; as late as August or September 1826, he found the time to answer Herschel's queries on the wave theory. It was Herschel who recommended Fresnel for the Royal Society's Rumford Medal.
Fresnel's cough worsened in the winter of 1826–1827, leaving him too ill to return to Mathieu in the spring. The Académie meeting of 30 April 1827 was the last that he attended. In early June he was carried to Ville-d'Avray, west of Paris. There his mother joined him. On 6 July, Arago arrived to deliver the Rumford Medal. Sensing Arago's distress, Fresnel whispered that "the most beautiful crown means little, when it is laid on the grave of a friend." Fresnel did not have the strength to reply to the Royal Society. He died eight days later, on Bastille Day.
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He is buried at Père Lachaise Cemetery, Paris. The is partly eroded away; the legible part says, when translated, "To the memory of Augustin Jean Fresnel, member of the Institute of France".
Posthumous publications.
Fresnel's "second memoir" on double refraction was not printed until late 1827, a few months after his death. Until then, the best published source on his work on double refraction was an extract of that memoir, printed in 1822. His final treatment of partial reflection and total internal reflection, read to the Académie in January 1823, was thought to be lost until it was rediscovered among the papers of the deceased Joseph Fourier (1768–1830), and was printed in 1831. Until then, it was known chiefly through an extract printed in 1823 and 1825. The memoir introducing the parallelepiped form of the Fresnel rhomb, read in March 1818, was mislaid until 1846, and then attracted such interest that it was soon republished in English. Most of Fresnel's writings on polarized light before 1821—including his first theory of chromatic polarization (submitted 7 October 1816) and the crucial "supplement" of January 1818—were not published in full until his "Oeuvres complètes" ("complete works") began to appear in 1866. The "supplement" of July 1816, proposing the "efficacious ray" and reporting the famous double-mirror experiment, met the same fate, as did the "first memoir" on double refraction.
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Publication of Fresnel's collected works was itself delayed by the deaths of successive editors. The task was initially entrusted to Félix Savary, who died in 1841. It was restarted twenty years later by the Ministry of Public Instruction. Of the three editors eventually named in the "Oeuvres", Sénarmont died in 1862, Verdet in 1866, and Léonor Fresnel in 1869, by which time only two of the three volumes had appeared. At the beginning of vol. 3 (1870), the completion of the project is described in a long footnote by "J. Lissajous."
Not included in the "Oeuvres" are two short notes by Fresnel on magnetism, which were discovered among Ampère's manuscripts. In response to Ørsted's discovery of electromagnetism in 1820, Ampère initially supposed that the field of a permanent magnet was due to a macroscopic circulating current. Fresnel suggested instead that there was a "microscopic" current circulating around each particle of the magnet. In his first note, he argued that microscopic currents, unlike macroscopic currents, would explain why a hollow cylindrical magnet does not lose its magnetism when cut longitudinally. In his second note, dated 5 July 1821, he further argued that a macroscopic current had the counterfactual implication that a permanent magnet should be hot, whereas microscopic currents circulating around the molecules might avoid the heating mechanism. He was not to know that the fundamental units of permanent magnetism are even smaller than molecules . The two notes, together with Ampère's acknowledgment, were eventually published in 1885.
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Lost works.
Fresnel's essay "Rêveries" of 1814 has not survived. The article "Sur les Différents Systèmes relatifs à la Théorie de la Lumière" ("On the Different Systems relating to the Theory of Light"), which Fresnel wrote for the newly launched English journal "European Review", was received by the publisher's agent in Paris in September 1824. The journal failed before Fresnel's contribution could be published. Fresnel tried unsuccessfully to recover the manuscript. The editors of his collected works were unable to find it, and concluded that it was probably lost.
Unfinished work.
Aether drag and aether density.
In 1810, Arago found experimentally that the degree of refraction of starlight does not depend on the direction of the earth's motion relative to the line of sight. In 1818, Fresnel showed that this result could be explained by the wave theory, on the hypothesis that if an object with refractive index formula_35 moved at velocity formula_36 relative to the external aether (taken as stationary), then the velocity of light inside the object gained the additional component formula_37. He supported that hypothesis by supposing that if the density of the external aether was taken as unity, the density of the internal aether was formula_38, of which the excess, namely formula_39, was dragged along at velocity formula_36, whence the "average" velocity of the internal aether was formula_37. The factor in parentheses, which Fresnel originally expressed in terms of wavelengths, became known as the "Fresnel drag coefficient".
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In his analysis of double refraction, Fresnel supposed that the different refractive indices in different directions within the "same medium" were due to a directional variation in elasticity, not density (because the concept of mass per unit volume is not directional). But in his treatment of partial reflection, he supposed that the different refractive indices of "different media" were due to different aether densities, not different elasticities.
Dispersion.
The analogy between light waves and transverse waves in elastic solids does not predict "dispersion"—that is, the frequency-dependence of the speed of propagation, which enables prisms to produce spectra and causes lenses to suffer from chromatic aberration. Fresnel, in "De la Lumière" and in the second supplement to his first memoir on double refraction, suggested that dispersion could be accounted for if the particles of the medium exerted forces on each other over distances that were significant fractions of a wavelength. Later, more than once, Fresnel referred to the demonstration of this result as being contained in a note appended to his "second memoir" on double refraction. No such note appeared in print, and the relevant manuscripts found after his death showed only that, around 1824, he was comparing refractive indices (measured by Fraunhofer) with a theoretical formula, the meaning of which was not fully explained.
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In the 1830s, Fresnel's suggestion was taken up by Cauchy, Baden Powell, and Philip Kelland, and it was found to be tolerably consistent with the variation of refractive indices with wavelength over the visible spectrum for a variety of transparent media . These investigations were enough to show that the wave theory was at least compatible with dispersion; if the model of dispersion was to be accurate over a wider range of frequencies, it needed to be modified so as to take account of resonances within the medium .
Conical refraction.
The analytical complexity of Fresnel's derivation of the ray-velocity surface was an implicit challenge to find a shorter path to the result. This was answered by MacCullagh in 1830, and by William Rowan Hamilton in 1832.
Legacy.
Within a century of Fresnel's initial stepped-lens proposal, more than 10,000 lights with Fresnel lenses were protecting lives and property around the world. Concerning the other benefits, the science historian Theresa H. Levitt has remarked:
In the history of physical optics, Fresnel's successful revival of the wave theory nominates him as the pivotal figure between Newton, who held that light consisted of corpuscles, and James Clerk Maxwell, who established that light waves are electromagnetic. Whereas Albert Einstein described Maxwell's work as "the most profound and the most fruitful that physics has experienced since the time of Newton," commentators of the era between Fresnel and Maxwell made similarly strong statements about Fresnel:
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What Whewell called the "true theory" has since undergone two major revisions. The first, by Maxwell, specified the physical fields whose variations constitute the waves of light. Without the benefit of this knowledge, Fresnel managed to construct the world's first coherent theory of light, showing in retrospect that his methods are applicable to multiple types of waves. The second revision, initiated by Einstein's explanation of the photoelectric effect, supposed that the energy of light waves was divided into quanta, which were eventually identified with particles called photons. But photons did not exactly correspond to Newton's corpuscles; for example, Newton's explanation of ordinary refraction required the corpuscles to travel faster in media of higher refractive index, which photons do not. Neither did photons displace waves; rather, they led to the paradox of wave–particle duality. Moreover, the phenomena studied by Fresnel, which included nearly all the optical phenomena known at his time, are still most easily explained in terms of the "wave" nature of light. So it was that, as late as 1927, the astronomer Eugène Michel Antoniadi declared Fresnel to be "the dominant figure in optics."
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Abbot
Abbot is an ecclesiastical title given to the head of an independent monastery for men in various Western Christian traditions. The name is derived from "abba", the Aramaic form of the Hebrew "ab", and means "father". The female equivalent is abbess.
Origins.
The title had its origin in the monasteries of Egypt and Syria, spread through the eastern Mediterranean, and soon became accepted generally in all languages as the designation of the head of a monastery. The word is derived from the Aramaic ' meaning "father" or ', meaning "my father" (it still has this meaning in contemporary Hebrew: אבא and Aramaic: ܐܒܐ) In the Septuagint, it was written as "abbas". At first it was employed as a respectful title for any monk, but it was soon restricted by canon law to certain priestly superiors. At times it was applied to various priests, e.g. at the court of the Frankish monarchy the ' ("of the palace"') and ' ("of the camp") were chaplains to the Merovingian and Carolingian sovereigns' court and army respectively. The title of abbot came into fairly general use in western monastic orders whose members include priests.
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Monastic history.
An abbot (from , ', from ("father"), from (), from '/' (, "father"); compare '; "") is the head and chief governor of a community of monks, called also in the East "hegumen" or "archimandrite". The English version for a female monastic head is abbess.
Early history.
In Egypt, the first home of monasticism, the jurisdiction of the abbot, or archimandrite, was but loosely defined. Sometimes he ruled over only one community, sometimes over several, each of which had its own abbot as well. Saint John Cassian speaks of an abbot of the Thebaid who had 500 monks under him. By the Rule of St Benedict, which, until the Cluniac reforms, was the norm in the West, the abbot has jurisdiction over only one community. The rule, as was inevitable, was subject to frequent violations; but it was not until the foundation of the Cluniac Order that the idea of a supreme abbot, exercising jurisdiction over all the houses of an order, was definitely recognised.
Monks, as a rule, were laymen, nor at the outset was the abbot any exception. For the reception of the sacraments, and for other religious offices, the abbot and his monks were commanded to attend the nearest church. This rule proved inconvenient when a monastery was situated in a desert or at a distance from a city, and necessity compelled the ordination of some monks. This innovation was not introduced without a struggle, ecclesiastical dignity being regarded as inconsistent with the higher spiritual life, but, before the close of the 5th century, at least in the East, abbots seem almost universally to have become deacons, if not priests. The change spread more slowly in the West, where the office of abbot was commonly filled by laymen till the end of the 7th century. The ecclesiastical leadership exercised by abbots despite their frequent lay status is proved by their attendance and votes at ecclesiastical councils. Thus at the first Council of Constantinople, AD 448, 23 archimandrites or abbots sign, with 30 bishops.
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The second Council of Nicaea, AD 787, recognized the right of abbots to ordain their monks to the inferior orders below the diaconate, a power usually reserved to bishops.
Abbots used to be subject to episcopal jurisdiction, and continued generally so, in fact, in the West till the 11th century. The Code of Justinian (lib. i. tit. iii. de Ep. leg. xl.) expressly subordinates the abbot to episcopal oversight. The first case recorded of the partial exemption of an abbot from episcopal control is that of Faustus, abbot of Lerins, at the council of Arles, AD 456; but the exorbitant claims and exactions of bishops, to which this repugnance to episcopal control is to be traced, far more than to the arrogance of abbots, rendered it increasingly frequent, and, in the 6th century, the practice of exempting religious houses partly or altogether from episcopal control, and making them responsible to the pope alone, received an impulse from Pope Gregory the Great. These exceptions, introduced with a good object, had grown into a widespread evil by the 12th century, virtually creating an "imperium in imperio," and depriving the bishop of all authority over the chief centres of influence in his diocese.
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Later Middle Ages.
In the 12th century, the abbots of Fulda claimed precedence of the archbishop of Cologne. Abbots more and more assumed almost episcopal state, and in defiance of the prohibition of early councils and the protests of St Bernard and others, adopted the episcopal insignia of mitre, ring, gloves and sandals.
It has been maintained that the right to wear mitres was sometimes granted by the popes to abbots before the 11th century, but the documents on which this claim is based are not genuine (J. Braun, "Liturgische Gewandung", p. 453). The first undoubted instance is the bull by which Alexander II in 1063 granted the use of the mitre to Egelsinus, abbot of the monastery of St Augustine at Canterbury. The mitred abbots in England were those of Abingdon, St Alban's, Bardney, Battle, Bury St Edmunds, St Augustine's Canterbury, Colchester, Croyland, Evesham, Glastonbury, Gloucester, St Benet's Hulme, Hyde, Malmesbury, Peterborough, Ramsey, Reading, Selby, Shrewsbury, Tavistock, Thorney, Westminster, Winchcombe, and St Mary's York. Of these the precedence was yielded to the abbot of Glastonbury, until in AD 1154 Adrian IV (Nicholas Breakspear) granted it to the abbot of St Alban's, in which monastery he had been brought up. Next after the abbot of St Alban's ranked the abbot of Westminster and then Ramsey. Elsewhere, the mitred abbots that sat in the Estates of Scotland were of Arbroath, Cambuskenneth, Coupar Angus, Dunfermline, Holyrood, Iona, Kelso, Kilwinning, Kinloss, Lindores, Paisley, Melrose, Scone, St Andrews Priory and Sweetheart. To distinguish abbots from bishops, it was ordained that their mitre should be made of less costly materials, and should not be ornamented with gold, a rule which was soon entirely disregarded, and that the crook of their pastoral staff (the crosier) should turn inwards instead of outwards, indicating that their jurisdiction was limited to their own house.
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The adoption of certain episcopal insignia (pontificalia) by abbots was followed by an encroachment on episcopal functions, which had to be specially but ineffectually guarded against by the Lateran council, AD 1123. In the East abbots, if in priests' orders and with the consent of the bishop, were, as we have seen, permitted by the second Nicene council, AD 787, to confer the tonsure and admit to the order of reader; but gradually abbots, in the West also, advanced higher claims, until we find them in AD 1489 permitted by Innocent IV to confer both the subdiaconate and diaconate. Of course, they always and everywhere had the power of admitting their own monks and vesting them with the religious habit.
The power of the abbot was paternal but absolute, limited, however, by the canon law. One of the main goals of monasticism was the purgation of self and selfishness, and obedience was seen as a path to that perfection. It was sacred duty to execute the abbot's orders, and even to act without his orders was sometimes considered a transgression. Examples among the Egyptian monks of this submission to the commands of the superiors, exalted into a virtue by those who regarded the entire crushing of the individual will as a goal, are detailed by Cassian and others, e.g. a monk watering a dry stick, day after day, for months, or endeavoring to remove a huge rock immensely exceeding his powers.
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Appointments.
When a vacancy occurred, the bishop of the diocese chose the abbot out of the monks of the monastery, but the right of election was transferred by jurisdiction to the monks themselves, reserving to the bishop the confirmation of the election and the benediction of the new abbot. In abbeys exempt from the archbishop's diocesan jurisdiction, the confirmation and benediction had to be conferred by the pope in person, the house being taxed with the expenses of the new abbot's journey to Rome. It was necessary that an abbot should be at least 30 years of age, of legitimate birth, a monk of the house for at least 10 years, unless it furnished no suitable candidate, when a liberty was allowed of electing from another monastery, well instructed himself, and able to instruct others, one also who had learned how to command by having practised obedience. In some exceptional cases an abbot was allowed to name his own successor. Cassian speaks of an abbot in Egypt doing this; and in later times we have another example in the case of St Bruno. Popes and sovereigns gradually encroached on the rights of the monks, until in Italy the pope had usurped the nomination of all abbots, and the king in France, with the exception of Cluny, Premontré and other houses, chiefs of their order. The election was for life, unless the abbot was canonically deprived by the chiefs of his order, or when he was directly subject to them, by the pope or the bishop, and also in England it was for a term of 8–12 years.
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The ceremony of the formal admission of a Benedictine abbot in medieval times is thus prescribed by the consuetudinary of Abingdon. The newly elected abbot was to put off his shoes at the door of the church, and proceed barefoot to meet the members of the house advancing in a procession. After proceeding up the nave, he was to kneel and pray at the topmost step of the entrance of the choir, into which he was to be introduced by the bishop or his commissary, and placed in his stall. The monks, then kneeling, gave him the kiss of peace on the hand, and rising, on the mouth, the abbot holding his staff of office. He then put on his shoes in the vestry, and a chapter was held, and the bishop or his delegate preached a suitable sermon.
General information.
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The ordinary attire of the abbot was according to rule to be the same as that of the monks. But by the 10th century the rule was commonly set aside, and we find frequent complaints of abbots dressing in silk, and adopting sumptuous attire. Some even laid aside the monastic habit altogether, and assumed a secular dress. With the increase of wealth and power, abbots had lost much of their special religious character, and become great lords, chiefly distinguished from lay lords by celibacy. Thus we hear of abbots going out to hunt, with their men carrying bows and arrows; keeping horses, dogs and huntsmen; and special mention is made of an abbot of Leicester , c. 1360, who was the most skilled of all the nobility in hare hunting. In magnificence of equipage and retinue the abbots vied with the first nobles of the realm. They rode on mules with gilded bridles, rich saddles and housings, carrying hawks on their wrist, followed by an immense train of attendants. The bells of the churches were rung as they passed. They associated on equal terms with laymen of the highest distinction, and shared all their pleasures and pursuits. This rank and power was, however, often used most beneficially. For instance, we read of Richard Whiting, the last abbot of Glastonbury, judicially murdered by Henry VIII, that his house was a kind of well-ordered court, where as many as 300 sons of noblemen and gentlemen, who had been sent to him for virtuous education, had been brought up, besides others of a lesser rank, whom he fitted for the universities. His table, attendance and officers were an honour to the nation. He would entertain as many as 500 persons of rank at one time, besides relieving the poor of the vicinity twice a week. He had his country houses and fisheries, and when he travelled to attend parliament his retinue amounted to upwards of 100 persons. The abbots of Cluny and Vendôme were, by virtue of their office, cardinals of the Roman church.
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In the process of time, the title abbot was extended to clerics who had no connection with the monastic system, as to the principal of a body of parochial clergy; and under the Carolingians to the chief chaplain of the king, ', or military chaplain of the emperor, ' It even came to be adopted by purely secular officials. Thus the chief magistrate of the republic at Genoa was called "".
Lay abbots (M. Lat. ', ', ', ', ' or ', ', or sometimes simply ') were the outcome of the growth of the feudal system from the 8th century onwards. The practice of commendation, by which—to meet a contemporary emergency—the revenues of the community were handed over to a lay lord, in return for his protection,
early suggested to the emperors and kings the expedient of rewarding their warriors with rich abbeys held "in commendam."
During the Carolingian epoch, the custom grew up of granting these as regular heritable fiefs or benefices, and by the 10th century, before the great Cluniac reform, the system was firmly established. Even the abbey of St Denis was held in commendam by Hugh Capet. The example of the kings was followed by the feudal nobles, sometimes by making a temporary concession permanent, sometimes without any form of commendation whatever. In England the abuse was rife in the 8th century, as may be gathered from the acts of the council of Cloveshoe. These lay abbacies were not merely a question of overlordship, but implied the concentration in lay hands of all the rights, immunities and jurisdiction of the foundations, i.e. the more or less complete secularization of spiritual institutions. The lay abbot took his recognized rank in the feudal hierarchy, and was free to dispose of his fief as in the case of any other. The enfeoffment of abbeys differed in form and degree. Sometimes the monks were directly subject to the lay abbot; sometimes he appointed a substitute to perform the spiritual functions, known usually as dean (), but also as abbot (', ', ").
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When the great reform of the 11th century had put an end to the direct jurisdiction of the lay abbots, the honorary title of abbot continued to be held by certain of the great feudal families, as late as the 13th century and later, with the head of the community retaining the title of dean. The connection of the lesser lay abbots with the abbeys, especially in the south of France, lasted longer; and certain feudal families retained the title of () for centuries, together with certain rights over the abbey lands or revenues. The abuse was not confined to the West. John, patriarch of Antioch at the beginning of the 12th century, informs us that in his time most monasteries had been handed over to laymen, ", for life, or for part of their lives, by the emperors.
Giraldus Cambrensis reported ("Itinerary", ii.iv) the common customs of lay abbots in the late 12th-century Church of Wales:
In conventual cathedrals, where the bishop occupied the place of the abbot, the functions usually devolving on the superior of the monastery were performed by a prior.
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Modern practices.
In the Roman Catholic Church, abbots continue to be elected by the monks of an abbey to lead them as their religious superior in those orders and monasteries that make use of the term (some orders of monks, as the Carthusians for instance, have only priors). A monastery must have been granted the status of an abbey by the pope, and such monasteries are normally raised to this level after showing a degree of stability—a certain number of monks in vows, a certain number of years of establishment, a certain firmness to the foundation in economic, vocational and legal aspects. Prior to this, the monastery would be a mere priory, headed by a prior who acts as superior but without the same degree of legal authority that an abbot has.
The abbot is chosen by the monks from among the fully professed monks. Once chosen, he must request blessing: the blessing of an abbot is celebrated by the bishop in whose diocese the monastery is or, with his permission, another abbot or bishop. The ceremony of such a blessing is similar in some aspects to the consecration of a bishop, with the new abbot being presented with the mitre, the ring, and the crosier as symbols of office and receiving the laying on of hands and blessing from the celebrant. Though the ceremony installs the new abbot into a position of legal authority, it does not confer further sacramental authority- it is not a further degree of Holy Orders (although some abbots have been ordained to the episcopacy).
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Once he has received this blessing, the abbot not only becomes father of his monks in a spiritual sense, but their major superior under canon law, and has the additional authority to confer the ministries of acolyte and lector (formerly, he could confer the minor orders, which are not sacraments, that these ministries have replaced). The abbey is a species of "exempt religious" in that it is, for the most part, answerable to the pope, or to the abbot primate, rather than to the local bishop.
The abbot wears the same habit as his fellow monks, though by tradition he adds to it a pectoral cross.
Territorial abbots follow all of the above, but in addition must receive a mandate of authority from the pope over the territory around the monastery for which they are responsible.
Abbatial hierarchy.
In some monastic families, there is a hierarchy of precedence or authority among abbots. In some cases, this is the result of an abbey being considered the "mother" of several "daughter" abbeys founded as dependent priories of the "mother". In other cases, abbeys have affiliated in networks known as "congregations". Some monastic families recognize one abbey as the motherhouse of the entire order.
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Modern abbots not as superior.
The title abbé (French; Ital. "abate"), as commonly used in the Catholic Church on the European continent, is the equivalent of the English "Father" (parallel etymology), being loosely applied to all who have received the tonsure. This use of the title is said to have originated in the right conceded to the king of France, by the concordat between Pope Leo X and Francis I (1516), to appoint commendatory abbots (') to most of the abbeys in France. The expectation of obtaining these sinecures drew young men towards the church in considerable numbers, and the class of abbés so formed' they were sometimes called, and sometimes (ironically) "" ("abbés of holy hope; or in a jeu de mots, "of St. Hope")came to hold a recognized position. The connection many of them had with the church was of the slenderest kind, consisting mainly in adopting the title of abbé, after a remarkably moderate course of theological study, practising celibacy and wearing distinctive dress, a short dark-violet coat with narrow collar. Being men of presumed learning and undoubted leisure, many of the class found admission to the houses of the French nobility as tutors or advisers. Nearly every great family had its abbé. The class did not survive the Revolution; but the courtesy title of abbé, having long lost all connection in people's minds with any special ecclesiastical function, remained as a convenient general term applicable to any clergyman.
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Eastern Christian.
In the Eastern Orthodox and Eastern Catholic Churches, the abbot is referred to as the "hegumen". The Superior of a monastery of nuns is called the "Hēguménē". The title of "archimandrite" (literally the head of the enclosure) used to mean something similar.
In the East, the principle set forth in the "Corpus Juris Civilis" still applies, whereby most abbots are immediately subject to the local bishop. Those monasteries which enjoy the status of being "stauropegic" will be subject only to a primate or his Synod of Bishops and not the local bishop.
Honorary and other uses of the title.
Although currently in the Western Church the title "abbot" is given only abbots of monasteries, the title archimandrite is given to "monastics" (i.e., celibate) priests in the East, even when not attached to a monastery, as an honor for service, similar to the title of monsignor in the Latin Church of the Catholic Church. In the Eastern Orthodox Church, only monastics are permitted to be elevated to the rank of archimandrite. Married priests are elevated to the parallel rank of Archpriest or Protopresbyter. Normally there are no celibate priests who are not monastics in the Orthodox Church, with the exception of married priests who have been widowed. Since the time of Catherine II the ranks of Abbot and Archimandrite have been given as honorary titles in the Russian Church, and may be given to any monastic, even if he does not in fact serve as the superior of a monastery. In Greek practice the title or function of Abbot corresponds to a person who serves as the head of a monastery, although the title of the Archimandrite may be given to any celibate priest who could serve as the head of a monastery.
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In the German Evangelical Church, the German title of "Abt" (abbot) is sometimes bestowed, like the French "abbé", as an honorary distinction, and survives to designate the heads of some monasteries converted at the Reformation into collegiate foundations.
Of these the most noteworthy is Loccum Abbey in Hanover, founded as a Cistercian house in 1163 by Count Wilbrand of Hallermund, and reformed in 1593. The abbot of Loccum, who still carries a pastoral staff, takes precedence over all the clergy of Hanover, and was "ex officio" a member of the consistory of the kingdom. The governing body of the abbey consists of the abbot, prior and the "convent", or community, of "Stiftsherren" (canons).
In the Church of England, the Bishop of Norwich, by royal decree given by Henry VIII, also holds the honorary title of "Abbot of St. Benet." This title hails back to England's separation from the See of Rome, when King Henry, as supreme head of the newly independent church, took over all of the monasteries, mainly for their possessions, except for St. Benet, which he spared because the abbot and his monks possessed no wealth, and lived like simple beggars, deposing the incumbent Bishop of Norwich and seating the abbot in his place, thus the dual title still held to this day.
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Additionally, at the enthronement of the Archbishop of Canterbury, there is a threefold enthronement, once in the throne the chancel as the diocesan bishop of Canterbury, once in the Chair of St. Augustine as the Primate of All England, and then once in the chapter-house as Titular Abbot of Canterbury.
There are several Benedictine abbeys throughout the Anglican Communion. Most of them have mitred abbots.
Abbots in art and literature.
"The Abbot" is one of the archetypes traditionally illustrated in scenes of "Danse Macabre".
The lives of numerous abbots make up a significant contribution to Christian hagiography, one of the most well-known being the "Life of St. Benedict of Nursia" by St. Gregory the Great.
During the years 1106–1107 AD, Daniel, a Russian Orthodox abbot, made a pilgrimage to the Holy Land and recorded his experiences. His diary was much-read throughout Russia, and at least seventy-five manuscript copies survive. Saint Joseph, Abbot of Volokolamsk, Russia (1439–1515), wrote a number of influential works against heresy, and about monastic and liturgical discipline, and Christian philanthropy.
In the "Tales of Redwall" series, the creatures of Redwall are led by an abbot or abbess. These "abbots" are appointed by the brothers and sisters of Redwall to serve as a superior and provide paternal care, much like real abbots.
"The Abbot" was a nickname of RZA from the Wu-Tang Clan.
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Ardipithecus
Ardipithecus is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a hominin is now a matter of debate. Two fossil species are described in the literature: "A. ramidus", which lived about 4.4 million years ago during the early Pliocene, and "A. kadabba", dated to approximately 5.6 million years ago (late Miocene). Initial behavioral analysis indicated that "Ardipithecus" could be very similar to chimpanzees; however, more recent analysis based on canine size and lack of canine sexual dimorphism indicates that "Ardipithecus" was characterised by reduced aggression, and that they more closely resemble bonobos.
Some analyses describe "Australopithecus" as being sister to "Ardipithecus ramidus" specifically. This means that "Australopithecus" is distinctly more closely related to "Ardipithecus ramidus" than "Ardipithecus kadabba". Cladistically, then, "Australopithecus" (and eventually "Homo sapiens") indeed emerged within the "Ardipithecus" lineage, and this lineage is not literally extinct.
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"Ardipithecus ramidus".
"A. ramidus" was named in September 1994. The first fossil found was dated to 4.4 million years ago on the basis of its stratigraphic position between two volcanic strata: the basal Gaala Tuff Complex (G.A.T.C.) and the Daam Aatu Basaltic Tuff (D.A.B.T.). The name "Ardipithecus ramidus" stems mostly from the Afar language, in which "Ardi" means "ground/floor" and "ramid" means "root". The "pithecus" portion of the name is from the Greek word for "ape".
Like most hominids, but unlike all previously recognized hominins, it had a grasping hallux or big toe adapted for locomotion in the trees. It is not confirmed how many other features of its skeleton reflect adaptation to bipedalism on the ground as well. Like later hominins, "Ardipithecus" had reduced canine teeth and reduced canine sexual dimorphism.
In 1992–1993 a research team headed by Tim White discovered the first "A. ramidus" fossils—seventeen fragments including skull, mandible, teeth and arm bones—from the Afar Depression in the Middle Awash river valley of Ethiopia. More fragments were recovered in 1994, amounting to 45% of the total skeleton. This fossil was originally described as a species of "Australopithecus", but White and his colleagues later published a note in the same journal renaming the fossil under a new genus, "Ardipithecus". Between 1999 and 2003, a multidisciplinary team led by Sileshi Semaw discovered bones and teeth of nine "A. ramidus" individuals at As Duma in the Gona area of Ethiopia's Afar Region. The fossils were dated to between 4.35 and 4.45 million years old.
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"Ardipithecus ramidus" had a small brain, measuring between 300 and 350 cm3. This is slightly smaller than a modern bonobo or female chimpanzee brain, but much smaller than the brain of australopithecines like Lucy (~400 to 550 cm3) and roughly 20% the size of the modern "Homo sapiens" brain. Like common chimpanzees, "A. ramidus" was much more prognathic than modern humans.
The teeth of "A. ramidus" lacked the specialization of other apes, and suggest that it was a generalized omnivore and frugivore (fruit eater) with a diet that did not depend heavily on foliage, fibrous plant material (roots, tubers, etc.), or hard and or abrasive food. The size of the upper canine tooth in "A. ramidus" males was not distinctly different from that of females. Their upper canines were less sharp than those of modern common chimpanzees in part because of this decreased upper canine size, as larger upper canines can be honed through wear against teeth in the lower mouth. The features of the upper canine in "A. ramidus" contrast with the sexual dimorphism observed in common chimpanzees, where males have significantly larger and sharper upper canine teeth than females. Of the living apes, bonobos have the smallest canine sexual dimorphism, although still greater than that displayed by "A. ramidus".
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The less pronounced nature of the upper canine teeth in "A. ramidus" has been used to infer aspects of the social behavior of the species and more ancestral hominids. In particular, it has been used to suggest that the last common ancestor of hominids and African apes was characterized by relatively little aggression between males and between groups. This is markedly different from social patterns in common chimpanzees, among which intermale and intergroup aggression are typically high. Researchers in a 2009 study said that this condition "compromises the living chimpanzee as a behavioral model for the ancestral hominid condition." Bonobo canine size and canine sexual dimorphism more closely resembles that of "A. ramidus", and as a result, bonobos are now suggested as a behavioural model.
"A. ramidus" existed more recently than the most recent common ancestor of humans and chimpanzees (CLCA or "Pan"-"Homo" LCA) and thus is not fully representative of that common ancestor. Nevertheless, it is in some ways unlike chimpanzees, suggesting that the common ancestor differs from the modern chimpanzee. After the chimpanzee and human lineages diverged, both underwent substantial evolutionary change. Chimp feet are specialized for grasping trees; "A. ramidus" feet are better suited for walking. The canine teeth of "A. ramidus" are smaller, and equal in size between males and females, which suggests reduced male-to-male conflict, increased pair-bonding, and increased parental investment. "Thus, fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools," the research team concluded.
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Ardi.
On October 1, 2009, paleontologists formally announced the discovery of the relatively complete "A. ramidus" fossil skeleton first unearthed in 1994. The fossil is the remains of a small-brained female, nicknamed "Ardi", and includes most of the skull and teeth, as well as the pelvis, hands, and feet. It was discovered in Ethiopia's harsh Afar desert at a site called Aramis in the Middle Awash region. Radiometric dating of the layers of volcanic ash encasing the deposits suggest that Ardi lived about 4.3 to 4.5 million years ago. This date, however, has been questioned by others. Fleagle and Kappelman suggest that the region in which Ardi was found is difficult to date radiometrically, and they argue that Ardi should be dated at 3.9 million years.<ref name="10.1038/nature09709"></ref>
The fossil is regarded by its describers as shedding light on a stage of human evolution about which little was known, more than a million years before Lucy ("Australopithecus afarensis"), the iconic early human ancestor candidate who lived 3.2 million years ago, and was discovered in 1974 just away from Ardi's discovery site. However, because the "Ardi" skeleton is no more than 200,000 years older than the earliest fossils of "Australopithecus", and may in fact be younger than they are, some researchers doubt that it can represent a direct ancestor of "Australopithecus".
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Some researchers infer from the form of her pelvis and limbs and the presence of her abductable hallux, that "Ardi" was a facultative biped: bipedal when moving on the ground, but quadrupedal when moving about in tree branches. "A. ramidus" had a more primitive walking ability than later hominids, and could not walk or run for long distances. The teeth suggest omnivory, and are more generalised than those of modern apes.
"Ardipithecus kadabba".
"Ardipithecus kadabba" is "known only from teeth and bits and pieces of skeletal bones", and is dated to approximately 5.6 million years ago. It has been described as a "probable chronospecies" (i.e. ancestor) of "A. ramidus". Although originally considered a subspecies of "A. ramidus", in 2004 anthropologists Yohannes Haile-Selassie, Gen Suwa, and Tim D. White published an article elevating "A. kadabba" to species level on the basis of newly discovered teeth from Ethiopia. These teeth show "primitive morphology and wear pattern" which demonstrate that "A. kadabba" is a distinct species from "A. ramidus".
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The specific name comes from the Afar word for "basal family ancestor".
Classification.
Due to several shared characteristics with chimpanzees, its closeness to ape divergence period, and due to its fossil incompleteness, the exact position of "Ardipithecus" in the fossil record is a subject of controversy. Primatologist Esteban Sarmiento had systematically compared and concluded that there is not sufficient anatomical evidence to support an exclusively human lineage. Sarmiento noted that "Ardipithecus" does not share any characteristics exclusive to humans, and some of its characteristics (those in the wrist and basicranium) suggest it diverged from humans prior to the human–gorilla last common ancestor. His comparative (narrow allometry) study in 2011 on the molar and body segment lengths (which included living primates of similar body size) noted that some dimensions including short upper limbs, and metacarpals are reminiscent of humans, but other dimensions such as long toes and relative molar surface area are great ape-like. Sarmiento concluded that such length measures can change back and forth during evolution and are not very good indicators of relatedness (homoplasy).
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However, some later studies still argue for its classification in the human lineage. In 2014, it was reported that the hand bones of "Ardipithecus", "Australopithecus sediba" and "A. afarensis" have the third metacarpal styloid process, which is absent in other apes. Unique brain organisations (such as lateral shift of the carotid foramina, mediolateral abbreviation of the lateral tympanic, and a shortened, trapezoidal basioccipital element) in "Ardipithecus" are also found only in the "Australopithecus" and "Homo". Comparison of the tooth root morphology with those of the earlier "Sahelanthropus" also indicated strong resemblance, also pointing to inclusion to the human line.
Evolutionary tree according to a 2019 study:
Paleobiology.
The "Ardipithecus" length measures are good indicators of function and together with dental isotope data and the fauna and flora from the fossil site indicate "Ardipithecus" was mainly a terrestrial quadruped collecting a large portion of its food on the ground. Its arboreal behaviors would have been limited and suspension from branches solely from the upper limbs rare. A comparative study in 2013 on carbon and oxygen stable isotopes within modern and fossil tooth enamel revealed that "Ardipithecus" fed both arboreally (on trees) and on the ground in a more open habitat, unlike chimpanzees.
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In 2015, Australian anthropologists Gary Clark and Maciej Henneberg said that "Ardipithecus" adults have a facial anatomy more similar to chimpanzee subadults than adults, with a less-projecting face and smaller canines (large canines in primate males are used to compete within mating hierarchies), and attributed this to a decrease in craniofacial growth in favour of brain growth. This is only seen in humans, so they argued that the species may show the first trend towards human social, parenting and sexual psychology. Previously, it was assumed that such ancient human ancestors behaved much like chimps, but this is no longer considered to be a viable comparison. This view has yet to be corroborated by more detailed studies of the growth of "A. ramidus". The study also provides support for Stephen Jay Gould's theory in "Ontogeny and Phylogeny" that the paedomorphic (childlike) form of early hominin craniofacial morphology results from dissociation of growth trajectories.
According to Scott Simpson, the Gona Project's physical anthropologist, the fossil evidence from the Middle Awash indicates that both "A. kadabba" and "A. ramidus" lived in "a mosaic of woodland and grasslands with lakes, swamps and springs nearby," but further research is needed to determine which habitat "Ardipithecus" at Gona preferred.
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Assembly line
An assembly line, often called "progressive assembly", is a manufacturing process where the unfinished product moves in a direct line from workstation to workstation, with parts added in sequence until the final product is completed. By mechanically moving parts to workstations and transferring the unfinished product from one workstation to another, a finished product can be assembled faster and with less labor than having workers carry parts to a stationary product.
Assembly lines are common methods of assembling complex items such as automobiles and other transportation equipment, household appliances and electronic goods.
Workers in charge of the works of assembly line are called assemblers.
Concepts.
Assembly lines are designed for the sequential organization of workers, tools or machines, and parts. The motion of workers is minimized to the extent possible. All parts or assemblies are handled either by conveyors or motorized vehicles such as forklifts, or gravity, with no manual trucking. Heavy lifting is done by machines such as overhead cranes or forklifts. Each worker typically performs one simple operation unless job rotation strategies are applied.
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According to Henry Ford:
Designing assembly lines is a well-established mathematical challenge, referred to as an assembly line balancing problem. In the simple assembly line balancing problem the aim is to assign a set of tasks that need to be performed on the workpiece to a sequence of workstations. Each task requires a given task duration for completion. The assignment of tasks to stations is typically limited by two constraints: (1) a precedence graph which indicates what other tasks need to be completed before a particular task can be initiated (e.g. not putting in a screw before drilling the hole) and (2) a cycle time which restricts the sum of task processing times which can be completed at each workstation before the work-piece is moved to the next station by the conveyor belt. Major planning problems for operating assembly lines include supply chain integration, inventory control and production scheduling.
Simple example.
Consider the assembly of a car: assume that certain steps in the assembly line are to install the engine, install the hood, and install the wheels (in that order, with arbitrary interstitial steps); only one of these steps can be done at a time. In traditional production, only one car would be assembled at a time. If engine installation takes 20 minutes, hood installation takes five minutes, and wheels installation takes 10 minutes, then a car can be produced every 35 minutes.
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In an assembly line, car assembly is split between several stations, all working simultaneously. When a station is finished with a car, it passes it on to the next. By having three stations, three cars can be operated on at the same time, each at a different stage of assembly.
After finishing its work on the first car, the engine installation crew can begin working on the second car. While the engine installation crew works on the second car, the first car can be moved to the hood station and fitted with a hood, then to the wheels station and be fitted with wheels. After the engine has been installed on the second car, the second car moves to the hood assembly. At the same time, the third car moves to the engine assembly. When the third car's engine has been mounted, it then can be moved to the hood station; meanwhile, subsequent cars (if any) can be moved to the engine installation station.
Assuming no loss of time when moving a car from one station to another, the longest stage on the assembly line determines the throughput (20 minutes for the engine installation) so a car can be produced every 20 minutes, once the first car taking 35 minutes has been produced.
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History.
Before the Industrial Revolution, most manufactured products were made individually by hand. A single craftsman or team of craftsmen would create each part of a product. They would use their skills and tools such as files and knives to create the individual parts. They would then assemble them into the final product, making cut-and-try changes in the parts until they fit and could work together (craft production).
Division of labor was practiced by Ancient Greeks, Chinese and other ancient civilizations. In Ancient Greece it was discussed by Plato and Xenophon. Adam Smith discussed the division of labour in the manufacture of pins at length in his book "The Wealth of Nations" (published in 1776).
The Venetian Arsenal, dating to about 1104, operated similar to a production line. Ships moved down a canal and were fitted by the various shops they passed. At the peak of its efficiency in the early 16th century, the Arsenal employed some 16,000 people who could apparently produce nearly one ship each day and could fit out, arm, and provision a newly built galley with standardized parts on an assembly-line basis. Although the Arsenal lasted until the early Industrial Revolution, production line methods did not become common even then.
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Industrial Revolution.
The Industrial Revolution led to a proliferation of manufacturing and invention. Many industries, notably textiles, firearms, clocks and watches, horse-drawn vehicles, railway locomotives, sewing machines, and bicycles, saw expeditious improvement in materials handling, machining, and assembly during the 19th century, although modern concepts such as industrial engineering and logistics had not yet been named.
The automatic flour mill built by Oliver Evans in 1785 was called the beginning of modern bulk material handling by Roe (1916). Evans's mill used a leather belt bucket elevator, screw conveyors, canvas belt conveyors, and other mechanical devices to completely automate the process of making flour. The innovation spread to other mills and breweries.
Probably the earliest industrial example of a linear and continuous assembly process is the Portsmouth Block Mills, built between 1801 and 1803. Marc Isambard Brunel (father of Isambard Kingdom Brunel), with the help of Henry Maudslay and others, designed 22 types of machine tools to make the parts for the rigging blocks used by the Royal Navy. This factory was so successful that it remained in use until the 1960s, with the workshop still visible at HM Dockyard in Portsmouth, and still containing some of the original machinery.
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One of the earliest examples of an almost modern factory layout, designed for easy material handling, was the Bridgewater Foundry. The factory grounds were bordered by the Bridgewater Canal and the Liverpool and Manchester Railway. The buildings were arranged in a line with a railway for carrying the work going through the buildings. Cranes were used for lifting the heavy work, which sometimes weighed in the tens of tons. The work passed sequentially through to erection of framework and final assembly.
The first flow assembly line was initiated at the factory of Richard Garrett & Sons, Leiston Works in Leiston in the English county of Suffolk for the manufacture of portable steam engines. The assembly line area was called 'The Long Shop' on account of its length and was fully operational by early 1853. The boiler was brought up from the foundry and put at the start of the line, and as it progressed through the building it would stop at various stages where new parts would be added. From the upper level, where other parts were made, the lighter parts would be lowered over a balcony and then fixed onto the machine on the ground level. When the machine reached the end of the shop, it would be completed.
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Interchangeable parts.
During the early 19th century, the development of machine tools such as the screw-cutting lathe, metal planer, and milling machine, and of toolpath control via jigs and fixtures, provided the prerequisites for the modern assembly line by making interchangeable parts a practical reality.
Late 19th-century steam and electric conveyors.
Steam-powered conveyor lifts began being used for loading and unloading ships some time in the last quarter of the 19th century. Hounshell (1984) shows a sketch of an electric-powered conveyor moving cans through a filling line in a canning factory.
The meatpacking industry of Chicago is believed to be one of the first industrial assembly lines (or disassembly lines) to be utilized in the United States starting in 1867. Workers would stand at fixed stations and a pulley system would bring the meat to each worker and they would complete one task. Henry Ford and others have written about the influence of this slaughterhouse practice on the later developments at Ford Motor Company.
20th century.
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According to Domm, the implementation of mass production of an automobile via an assembly line may be credited to Ransom Olds, who used it to build the first mass-produced automobile, the Oldsmobile Curved Dash. Olds patented the assembly line concept, which he put to work in his Olds Motor Vehicle Company factory in 1901.
At Ford Motor Company, the assembly line was introduced by William "Pa" Klann upon his return from visiting Swift & Company's slaughterhouse in Chicago and viewing what was referred to as the "disassembly line", where carcasses were butchered as they moved along a conveyor. The efficiency of one person removing the same piece over and over without moving to another station caught his attention. He reported the idea to Peter E. Martin, soon to be head of Ford production, who was doubtful at the time but encouraged him to proceed. Others at Ford have claimed to have put the idea forth to Henry Ford, but Pa Klann's slaughterhouse revelation is well documented in the archives at the Henry Ford Museum and elsewhere, making him an important contributor to the modern automated assembly line concept. Ford was appreciative, having visited the highly automated 40-acre Sears mail order handling facility around 1906. At Ford, the process was an evolution by trial and error of a team consisting primarily of Peter E. Martin, the factory superintendent; Charles E. Sorensen, Martin's assistant; Clarence W. Avery; C. Harold Wills, draftsman and toolmaker; Charles Ebender; and József Galamb. Some of the groundwork for such development had recently been laid by the intelligent layout of machine tool placement that Walter Flanders had been doing at Ford up to 1908.
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The moving assembly line was developed for the Ford Model T and began operation on October 7, 1913, at the Highland Park Ford Plant, and continued to evolve after that, using time and motion study. The assembly line, driven by conveyor belts, reduced production time for a Model T to just 93 minutes by dividing the process into 45 steps. Producing cars quicker than paint of the day could dry, it had an immense influence on the world.
In 1922, Ford (through his ghostwriter Crowther) said of his 1913 assembly line:
Charles E. Sorensen, in his 1956 memoir "My Forty Years with Ford", presented a different version of development that was not so much about individual "inventors" as a gradual, logical development of industrial engineering:
As a result of these developments in method, Ford's cars came off the line in three-minute intervals or six feet per minute. This was much faster than previous methods, increasing production by eight to one (requiring 12.5 man-hours before, 1 hour 33 minutes after), while using less manpower. It was so successful, paint became a bottleneck. Only japan black would dry fast enough, forcing the company to drop the variety of colours available before 1914, until fast-drying Duco lacquer was developed in 1926.
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The assembly line technique was an integral part of the diffusion of the automobile into American society. Decreased costs of production allowed the cost of the Model T to fall within the budget of the American middle class. In 1908, the price of a Model T was around $825, and by 1912 it had decreased to around $575. This price reduction is comparable to a reduction from $15,000 to $10,000 in dollar terms from the year 2000. In 1914, an assembly line worker could buy a Model T with four months' pay.
Ford's complex safety procedures—especially assigning each worker to a specific location instead of allowing them to roam about—dramatically reduced the rate of injury. The combination of high wages and high efficiency is called "Fordism", and was copied by most major industries. The efficiency gains from the assembly line also coincided with the take-off of the United States. The assembly line forced workers to work at a certain pace with very repetitive motions which led to more output per worker while other countries were using less productive methods.
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In the automotive industry, its success was dominating, and quickly spread worldwide. Ford France and Ford Britain in 1911, Ford Denmark 1923, Ford Germany and Ford Japan 1925; in 1919, Vulcan (Southport, Lancashire) was the first native European manufacturer to adopt it. Soon, companies had to have assembly lines, or risk going broke by not being able to compete; by 1930, 250 companies which did not had disappeared.
The massive demand for military hardware in World War II prompted assembly-line techniques in shipbuilding and aircraft production. Thousands of Liberty ships were built making extensive use of prefabrication, enabling ship assembly to be completed in weeks or even days. After having produced fewer than 3,000 planes for the United States Military in 1939, American aircraft manufacturers built over 300,000 planes in World War II. Vultee pioneered the use of the powered assembly line for aircraft manufacturing. Other companies quickly followed. As William S. Knudsen (having worked at Ford, GM and the National Defense Advisory Commission) observed, "We won because we smothered the enemy in an avalanche of production, the like of which he had never seen, nor dreamed possible."
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Improved working conditions.
In his 1922 autobiography, Henry Ford mentions several benefits of the assembly line including:
The gains in productivity allowed Ford to increase worker pay from $1.50 per day to $5.00 per day once employees reached three years of service on the assembly line. Ford continued on to reduce the hourly work week while continuously lowering the Model T price. These goals appear altruistic; however, it has been argued that they were implemented by Ford in order to reduce high employee turnover: when the assembly line was introduced in 1913, it was discovered that "every time the company wanted to add 100 men to its factory personnel, it was necessary to hire 963" in order to counteract the natural distaste the assembly line seems to have inspired.
Sociological problems.
Sociological work has explored the social alienation and boredom that many workers feel because of the repetition of doing the same specialized task all day long.
Karl Marx expressed in his theory of alienation the belief that, in order to achieve job satisfaction, workers need to see themselves in the objects they have created, that products should be "mirrors in which workers see their reflected essential nature". Marx viewed labour as a chance for people to externalize facets of their personalities. Marxists argue that performing repetitive, specialized tasks causes a feeling of disconnection between what a worker does all day, who they really are, and what they would ideally be able to contribute to society. Furthermore, Marx views these specialised jobs as insecure, since the worker is expendable as soon as costs rise and technology can replace more expensive human labour.
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Since workers have to stand in the same place for hours and repeat the same motion hundreds of times per day, repetitive stress injuries are a possible pathology of occupational safety. Industrial noise also proved dangerous. When it was not too high, workers were often prohibited from talking. Charles Piaget, a skilled worker at the LIP factory, recalled that besides being prohibited from speaking, the semi-skilled workers had only 25 centimeters in which to move. Industrial ergonomics later tried to minimize physical trauma.
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Adelaide
Adelaide ( , ; ) is the capital and most populous city of South Australia, as well as the fifth-most populous city in Australia. The name "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The demonym "Adelaidean" is used to denote the city and the residents of Adelaide. The traditional owners of the Adelaide region are the Kaurna. The name in their language refers to the area of the city centre and surrounding Park Lands. Adelaide is situated on the Adelaide Plains north of the Fleurieu Peninsula, between the Gulf St Vincent in the west and the Mount Lofty Ranges in the east. Its metropolitan area extends from the coast to the foothills of the Mount Lofty Ranges, and stretches from Gawler in the north to Sellicks Beach in the south.
Named in honour of Adelaide of Saxe-Meiningen, wife of King William IV, the city was founded in 1836 as the planned capital for the only freely settled British province in Australia, distinguishing it from Australia's penal colonies. Colonel William Light, one of Adelaide's founding fathers, designed the city centre and chose its location close to the River Torrens. Light's design, now listed as national heritage, set out the city centre in a grid layout known as "Light's Vision", interspaced by wide boulevards and large public squares, and entirely surrounded by park lands. Colonial Adelaide was noted for its leading examples of religious freedom and progressive political reforms and became known as the "City of Churches" due to its diversity of faiths. It was Australia's third-most populous city until the postwar era.
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Today, Adelaide is one of Australia's most visited travel destinations and hosts , such as the Adelaide 500, Tour Down Under, LIV Golf Adelaide, and the Adelaide Fringe, the world's second largest annual arts festival, contributing to its rising tourism sector. The city has also been renowned for its automotive industry, having been the original host of the Australian Grand Prix in the FIA Formula One World Championship from 1985 to 1995. Other features include its food and wine industries, its coastline and hills, its large defence and manufacturing operations, and its emerging space sector, including the Australian Space Agency being headquartered there. Adelaide routinely ranks among the world's most liveable cities, at one stage being named the most liveable city in the country, third in the world. Its aesthetic appeal has also been recognised by "Architectural Digest", which ranked Adelaide as the most beautiful city in the world in 2024.
As South Australia's government and commercial centre, Adelaide is the site of many governmental and financial institutions. Most of these are concentrated in the central business district along the cultural boulevards of North Terrace and King William Street. Adelaide has also been classed as a Gamma + level global city as categorised by the Globalization and World Cities Research Network, with the city further linking economic regions to the worldwide economy. Adelaide is connected by extensive bus, train and tram networks, all of which are operated by Adelaide Metro with its main railway terminus at the Adelaide railway station. The city is also served by Adelaide Airport, the nation's fifth largest airport, for air travel. Additionally, Port Adelaide serves as Adelaide's hub for sea travel, as well as its main seaport.
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History.
Before European settlement.
The area around modern-day Adelaide was originally inhabited by the Kaurna people, one of many Aboriginal tribes in South Australia. The city and parklands area also known as "Tarntanya", "Tandanya" (now the short name of Tandanya National Aboriginal Cultural Institute), "Tarndanya", or "Tarndanyangga" (now the dual name for Victoria Square in the Kaurna language). The name means 'male red kangaroo rock', referring to a rock formation on the site that has now been destroyed.
The surrounding area was an open, grassy plain with patches of trees and shrubs, which had been managed by hundreds of generations. Kaurna country encompassed the plains stretching north and south of Tarntanya, as well as the wooded foothills of the Mt Lofty Ranges. The River Torrens was known as the Karrawirra Pari (Red Gum forest river). About 300 Kaurna populated the Adelaide area, and were referred to by the settlers as the Cowandilla.
The more than 20 local clans across the plain lived seminomadic lives, with extensive mound settlements where huts were built repeatedly over centuries and a complex social structure, including a class of sorcerers separated from regular society.
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Within a few decades of European settlement of South Australia, Kaurna culture was almost completely lost. The last speaker of Kaurna language died in 1929. Extensive documentation by early missionaries and other researchers has enabled a modern revival of both, which has included a commitment by local and state governments to rename or include Kaurna names for many local places.
19th century.
Based on the ideas of Edward Gibbon Wakefield about colonial reform, Robert Gouger petitioned the British government to create a new colony in Australia, resulting in the passage of the South Australia Act 1834. Physical establishment of the colony began with the arrival of the first British colonisers in February 1836. The first governor
proclaimed the commencement of colonial government in South Australia on 28 December 1836, near The Old Gum Tree in what is now the suburb of Glenelg North. The event is commemorated in South Australia as Proclamation Day. The site of the colony's capital was surveyed and laid out by Colonel William Light, the first surveyor-general of South Australia, with his own original, unique, topographically sensitive design. The city was named after Queen Adelaide.
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