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ities of absorption and of radiation are the same if the temperature of the substance is the same in the two cases. While if the temperature of either condition is decreased, so is the intensity of the effect. Thus, if a white- hot solid is placed behind a quantity of cooler gas or vapor, the absorption spectrum is a c...
," " a " and " B " " bands " are due to absorption by the oxygen in the air, while numerous other lines are due to the presence of water vapor. A method for distinguishing between solar and terrestrial lines will be described presently. Similarly, by a study of the spectra of the stars, either emission or absorption, a...
, because of the rotation of the sun. Hut those lines in the spectrum due to absorption in the earth's atmosphere will not be so displaced. student should consult Ames, Prismatic and Diffraction Spectra, for Fraunhofer's original memoirs, and Brace, The * of Radiation and Absorption, for the memoirs of Kin-h- hoff :.nd...
include all the other trains of waves, which will combine in the eye to pro- duce a definite color, called the " complementary color " of that of the waves which were absorbed. If the body absorbs two trains of waves, it may happen that the intensity of the absorption is not the same for both trains ; that is, it may ...
in produc- ing other waves, which are therefore radiated in all direc- tions, the phenomenon is called, as has been said, fluorescence. The fluorescent light consists in general of waves whose wave length is longer than that of the waves whose absorp- tion produces the fluorescence. In this case the color of the trans...
and invisible) reaches the earth from the sun. Dispersion It is not necessary to say anything here in regard to the dispersive action of prisms, gratings, etc., but a few illustra- tions may be given of colors due to it. Prismatic <lis\|>«TM(»n is slmun by rainlmws, halos around the sun and moon, dew- drops, diamonds w...
parts which are intimately connected with the endings of the optic nerve. The exact mode of excitation of these nerve endings by the incident ether waves is not known. Certain portions of the retina, viz., those remote from its centre, play no part in color sensation ; for, when waves of all wave lengths lying within ...
the retina they stimulate the "red," "green," and "blue" sets of nerves to degrees which are proportional to F 1, F 2, and F 3, the phenomena of color sensation have been explained. BOOKS OF REFERENCE ;:. Light for Adranoed Students. London. 1902. An excellent text-hook, contain in.: <!• •-••n\|'tioiis of all the funda...
lose its magnetism very easily, if it is jarred or subjected to an increase in temperature; but this is not true of the piece of steel — it remains a magnet under all ordinary conditions. All magnets in ordinary use are made therefore of steel, some kinds of which are much better than others. Much progress in this res...
ISM importance of the medium in the consideration of magnetic phenomena is shown. Poles. — If an iron or steel rod or " needle " is magnetized by means of a long solenoid, and if it is then removed and suspended by a fine thread or 011 a vertical pivot, so that it is free to rotate in a horizontal plane, it will turn a...
is hammered or twisted or heated, its magnetism is altered. as is shown by a change in the force which it exerts upon another magnet or upon a piece of iron at a fixed distance from it. Induction. — We make the assumption, then, that each molecule of a magnetic substance, e.g. of a piece of iron, or of nickel, etc., i...
"; or the former is said to be magnetized by "in- duction." Strictly speaking, these names apply to the phe- nomenon only so long as the magnetizing magnet is kept in its position near the magnetic substance ; when the two are separated, the latter remains a magnet, although a weaker one, for a greater or less time, as...
of Rn and Rt measured along the magnet, and if this special bar magnet is made of the length Z, it might replace the former so far as action at a considerable distance is concerned. The forces on the two ends of the latter magnet due to the distant one are then equal in amount but opposite in direction. We are therefo...
Lines of force do not, of course, have a physical existence ; and the above statements are simply descriptions of the appearance of their geometrical curves. By means of these ideas it is often possible to give simple descriptions of com- FIG. 317 a. — Bar of soft iron placed in a uniform magnetic field. plicated case...
a great than for a small distance. Coulomb made the assumption that, so far as distance was concerned, the force varied inversely as its square. So calling this distance r, the law of action of two poles is assumed to be that the force between them is proportional to — ^> This is known as Coulomb's Law, and it was ver...
us assume the simplest case, viz., that the charges are entirely at the ends ; then, if the magnet is short, the forces at the two ends are equal in amount, although opposite in direction, because the two ends are at almost the same point in the field. The "intensity" of the field at any point is defined to be the val...
- m m 2 m/r But if r is very great in comparison with Z, /=— ::ir-, 2 m/r 2 A/ Consequently, substituting in the formula for tan JV, M r* tan N Various precautions and modifications for this experiment are explained in laboratory manuals, but it is evident that * = — 2— both r and N can be measured ; and so — may be d...
words, the intensity of the field at any point is proportional to the number of tubes per unit area at that point. Magnetic Induction. — As was explained on page 605, and as is apparent from the cuts on that page, the effect of intro- ducing a piece of iron or other magnetic material into a field of force in air is to...
; and so we are led to believe that the energy is MAGNETIC FORCE AND INDUCTION 617 located in the surrounding medium where the magnetic field exists. It follows from the formula that / is small if //. is huL,re, or, in words, the forces are small if the permeability of the medium is large ; and consequently in such a m...
. th<-i<!•»•. it it moves up iin.l \\at.-r rrj.Isu-."* it. tin- potential energy is again decreased. CHAPTER XLI MAGNETISM OF THE EARTH Magnetic Elements. — The fact that there is a magnetic field of force on the surface of the earth is proved by the ob- servations on the motion of a suspended magnet, which were referr...
on pages 610-613. Therefore, since the angle of dip, N, can be measured directly, the value of R may be deduced. Further, if the ratio of the horizontal and vertical components can be meas- ured, the dip may be calculated ; for, calling these H and V* "26. — Diagram rep- resenting the horizontal and vertical component...
through whose position on the map any one line passes, the value of the declination (or variation) is the same. Such lines are called "isog- onals," and are of the greatest possible assistance to mariners and surveyors. They are shown in the cut for the year 1900, and each one is marked with a certain number, e.g. 5°,...
variation t'mm place to place were made by Columbus in Hart man is reputed to have di.senvn-ed the dip in 1644. He obtained a value of 9° when- he should have obtained 624 MAGNETISM 70°. This fact was not published, and Norman, in 1576, independently discovered it in London, obtaining a value of 71° 50'. Norman was pr...
The same phenomena may be observed with any two por- tions.)f different kinds of matter; but with certain kinds the forces of attraction are manifested, not alone by those portions of the surface where they were in contact with the other body, but also over all their surface. This is true of metals, for instance. So, ...
, because, as stated above, when two bodies are charged by rubbing them against each other and then separating them, one attracts the other, and this proves that in order to separate them work was required. In other words, work is necessary in order to have electrical charges. This energy which is associated with charg...
nt s jn that 628 ELECTROSTATICS glass rubbed with silk is charged positively ; and that the silk is charged negatively. Similarly, in all cases, experi- ments show that when any two bodies are brought in con- tact and then separated, they are charged oppositely. If different charged bodies are suspended in turn, it is ...
surface. (This is true only after the charges have come to rest ; it does not hold when there are currents.) This fact may be proved by direct experiment in many ways. Faraday made a metal box large enough to allow him to enter it and carry with him his instruments ; and he showed that, however the box was charged, th...
sitely on its two ends or faces, as described above. There is an essential difference, however, between this case and that of a piece of non-conductor, owing to the fact that lines of force do not pass through a conductor and, there- fore, end on its surface, while they can and do pass through a non-conductor. This di...
be drawn to the latter, and "discharge " it by neutrali/in^ the charges on it; the other induced charges, which are like tlmse on the body originally charged, will remain on the eondiu -tor. The final action, therefore, is as if the obi 634 ELECTRO 8T A TICS were bodily transferred to the pointed conductor. This actio...
35 urc of the force. It is obvious that a single gold leaf could be used in place of the pith hall, or that two pith halls could be used in place of the two gold leaves in the former instrument. Electrical Machines. — As we have seen, electrical charges may be produced by two independent methods: by friction or contact...
or otherwise connected to the earth ; so the negative charge is removed, and only the positive one re- mains. Connection with the earth is now broken, and if the cap is lifted by its handle, it will carry with it its positive charge. This charge may be transferred to some conductor ; and the cap being discharged may b...
silk and a piece of glass, the leaves do not diverge, even when these two bodies are touched or rubbed together and then separated. But, if one of them is now removed, the leaves do diverge, showing that the two bodies were charged, but with exactly equal amounts of opposite kinds of electric- ity. Similarly, if an in...
same whatever non-conducting medium is used to fill the vessel or is present in it: air, oil, sulphur, etc. Thus, electri- cal effects are transmitted through these various substances; and for that reason Faraday called them "dielectrics." (Actually there is a distinction between the idea of a dielectric and that of a...
Induction. — The "intensity" of an electric field of force at any point is defined to be the value of the force \vhieh would act on a unit positive charge if placed at that point. Kxactly as in the case of a magnetic field, too, tubes hounded by lines of electric force can be drawn; and if they are of the proper size ...
of non-conductor. The action of charges on each other has already been discussed. Electric Potential. — The properties of electric charges and the condition for their being in equilibrium may be expressed in a different manner. When a charge is moved in an elec- tric field, work is done, either at the expense of the e...
an equipotential surface. The direction of the force is, obviously, from points of high to those of low potential. Similarly, in the case of electrical phenomena, we may >se the earth as our standard body, since it is a con- ductor, and is so large that its electrical condition ma\ In- regarded as permanent, and may d...
conductor. „ the equipotential surfaces are con- centric spheres, and the lines of force are portions of radii starting from the spherical conductor. If the charge on the conductor is plus, the potential at points near it is higher than that at those more distant ; if the charge is negative, just the reverse is true. ...
, and they are so distributed that the inten- sity at any point inside is zero, or, what is the same thing, that the potential at all points is the same. Thus, consider a closed FI«. 347. -Diagram illustrating the conductor of any shape, and let P fact that the force inside a closed con- be any point in its interior an...
spark passing between them, and a connection may be found by experiment between the potential difference and the spark length in any dielectric under definite conditions. A limit is therefore fixed by the electric properties or " strength " of the air for the value to which the potential of a conductor may be raised; ...
to carry to it a unit plus charge from the earth; while if the dielectric has the value jfiT, the forces are dimin- ished JT-fold (since the electric forces vary inversely as 7f ), and the potential of the conductor, F^, or the work now re- quired to bring up a unit plus charge, is less than VA in the ratio 1 : K\ or,...
in the bringing up to it from the earth a series of minute charges. In this manner the charge grad- ually increases from 0 to its final value, e ; and the potential rises from 0 to F". Since the potential at an instant varies directly as the charge at that moment, the mean value of the potential during the process is ...
c- tric charge moves from points of high to those of low poten- tial. When a gas is compressed by a pump into a vessel of any kind, the pressure continues to increase until a point is reached at which the vessel breaks or the gas leaks, and this maximum pressure does not depend upon the size of the vessel, but upon its...
air between the plates; for if K is increased, the force required to move a charge is decreased. Therefore, in the end practically all the charge on the first plate is on the face toward the second one, and there is an equal amount ot electricity of the opposite kind on that lace of the second plate which is toward th...
seillat ion jirudiicus waves. Kxperim- lia\i-.sliown that ihe^- waves tra\«-l in air with the vel<> of li^lit ami that thev are t rans\ ers.-. I IP ean In- relli-j-ted, • ;:>• ; ELECTROSTA TICS refracted, diffracted, polarized, etc. Their wave lengths can be measured, and waves as short as a small fraction of a cen- ti...
CE 657 those of the second, P2 and Qv etc.; and let them be always charged in such a manner that Pp Pa, etc., are positive, and Qv Qv etc., are nega- tive Then, if Px, Pv p,. f. P. 1 r. p3( etc., are connected by wires, and (>r 0* etc., are also connected, the FIG. 858. — Three condensers joined in parallel. condensers...
if their difference AMES1* PHT81C8 - 42 658 ELECT It OSTA TIC 8 of potential is incrt-usi'd, joining condensers in series in- creases their sparking distance. (When two or more con- densers are joined in series, the minus charge on Ql does not combine with the equal plus charge on P2, etc., until Pl is joined to Qn. B...
of potential of its two sets of quadrants. Thus, two differences of potential may be compared by measuring the corresponding deflections of the needle. In order, however, to measure any one difference of poten- tial, a different instrument must be used. This is the "absolute electrometer," which was also invented by L...
, known, e.g. a parallel plate FIO. 867.— cavendish's method of comparing condenser the distance apart of whose plates can be varied. The method is as follows : let Av B1 and Av J?2 be the two condensers ; charge them by joining A1 and A% to some electrical machine, while Bl and B% are joined to the earth ; then discon...
the point of a conductor which is joined to an electrometer, and let some means be adopted to have a continuous current of small conducting particles leave it. Let B be such a particle. Then if the potential of A is higher than that of points in the air near it, a plus charge will he induced on B and a minus one on A ...
in the opposite manner, while other portions of the glass do not relax completely; these two portions, however, balance each other for the moment, and there is no resultant strain ; as time goes on, however, these strains, not being maintained by any force, gradually relax, but not to the same degree, so there is agai...
, more often, "the current." If the current is steady, the quantities ij and izt pass in an interval of time t ; and (tj + iz)t is called the " quantity of the current." If the current is not steady, and if in any interval of time the quan- tities of plus and minus charges that pass are e1 and ez, the quantity of curre...
665 rent. (The heat produced in the conductor may be meas- mvil if it is in the form of a wire by coiling it in a calorimeter of water. See chapter XII. If the C.G.S. system of units is used in defining the unit quantity of electricity, the product iEt is a certain number of ergs; and so the heat produced must be expr...
even then under the action of a current in one direction it decomposes and breaks down. Therefore the process of using the lamp is first to raise the temperature of the filament until it becomes conducting, and then to have it traversed by a current whose direction is reversed at short intervals. If this is done, the ...
cause ELECTRODYNAMICS them to diverge still farther. In this manner, then, it may be determined whether F2 > Fr or F^< V^\ if the former is the case, and if a wire is made to join the two conductors, the direction of the current is from the one at potential V% to the one at potential Vl ; in the contrary case, the dir...
. -An astatic combination to other actions than those of the current in the coils, is to attach rigidly to it another magnet of equal magnetic moment, but turned so that its axis is in an opposite direction. Thus, a north pole of one comes opposite to the south pole of the other. If, now, one of -<j magnets is inclosed...
a current from A to B, the lines of magnetic force near it are as shown ; or, if the total electric circuit is considered, the lines of force pass through it from one side, and return outside. Thus, a current and any one of its lines of magnetic force form two closed links threading each other, like two links of a cha...
the magnetic meridian when it comes to rest, the moment due to the earth's force is JIM sin N; and that due to the electric current is /M"cos N. Since these must bal- ance each other, or FIG. 368.— Tangent galvanometer. Therefore the strength of the current is meas- ured by the tangent of the angle of deflection ; tha...
of the magnet, An instrument specially designed to measure quantities of current, as distinguished from current strengths, is called a " ballistic " galvanometer. Measurement of Electro-motive Force. — Since an electro- motive force is a difference of potential, it may be measured by any electrometer. (See page 658.) ...
etc., it is possible to maintain a constant difference of potential between two conductors, a steady current may be produced by connecting these two conductors by a wire or other conductor. There are at least four methods by which this constant diffen -nee in potential may be produced. 1 in electrical machine such as ...
is observed, further, that there is a current also through the dilute acid, and that its direction is from the zinc to the copper. Thus the current flows in a circuit; FIG. 870.— Voltaic cell. PRODUCTION OF ELECTRIC CUliliK\T.< 677 outside the liquid, from copper to zinc ; inside the liquid, from zinc to copper. Since...
, it possible, because the zinc consumed in producing 678 them is \\;i>tr<l. This can be done in many cases by rubbing mercury over the xinc rod before it is immersed in the liquid, and thus making a surface of mercury amalgam with the metal, which is practically uniform. As the current flows in a voltaic cell, hydroge...
is to make what is practically one (dl \viili poles n times as large; this does not affect the difference of potential between the poles. A mechanical analogy of a simple voltaic cell is furnished by a pump or paddle wheel working in a horizontal tube connecting two tall vertical pipes containing some liquid, such as ...
when it is higher, in others when it is cuit made up of two con- lower, — there comes a point when the doctors i and //, having current begins to decrease, and finally junctions at A and B. ° J one at which the current ceases; while if the difference in temperature is increased still more, a current is produced, but i...
-motive force " E at the boundary. The proof of the existence of this E. M. F. across the surface of contact is afforded if P and Q are conductors, and if an electric current is forced by some source, such as a voltaic cell, across this surface, first in the direction from P to (), then in the opposite direction. It is...
then Sir William Thomson — by the following experiment : let an electric current be forced through a wire of some definite material whose ends are kept at a higher temperature than its middle point, and let the temperatures be noted at two intermediate points, one in each half, which are such that their temperatures a...
thermocouple may be placed at them. The sensitiveness of the instru- ment may be increased by joining in series several pairs of tli«- two conductors, as shown in the cut. If the alternate junctions are kept at one temperature, and the other junctions are kept at a different one, the current will be increased; and so ...
substances which are evolved at the anode and the cathode in different electrolytes. It is found that hydrogen and all metals are liberated at the cathode, while oxygen, chlorine, iodine, etc., are liberated at the anode. Further, the amounts of the substances evolved under dif- ferent conditions were systematically s...
that radical. Thus, the valence of hydrogen and of chlorine is one; that of oxygen and of SO4 is two ; etc. Experiments show that if any molecule is regarded as made up of two parts, the valences of the two parts are the same. Thus, since a mole- cule of copper sulphate is CuSO4, the valence of copper is two, as is sh...
and suitable precautions are taken to prevent any mechanical currents in the liquid, for it is found that they, for purely chemical reasons, affect slightly the quantity deposited. FIG. 879. — A simple form of silver voltameter. Electro-chemical Equivalent. — By means of Faraday's second law we can calculate the relat...
" ions "; and those which move toward the cathode he called "cations," while those which move toward the anode he called "anions." Thus all cations are positively charged; all anions, negatively. The electric current in the electrolyte consists, then, from this point of view, of the passage in opposite directions of t...
its electro-chemical equivalent. This may be described differently : When a unit quantity of electricity passes, tj + «2 = 1 ; if ml and m2 are the electro-chemical equivalents of the two sets of ions, m1 and m2 grams are liberated at the two elec- trodes in this interval of time. The liberation of the m1 grams at the...
and so the ratio lie mass of the former to that of the latter is equal to that of their chemical equivalents; this is the second law. On this assumption, the charge carried on an ion whose valence is one is the smallest charge involved in electrolysis. It is called an "atom of electricity." Nature of Ions. - The quest...
lowered into the solution ; the positively charged ions move toward the cathode during their intervals of existence, before they com- bine with other ions and form electrically neutral molecules ; the negatively charged ones move toward the anode. The fact should be emphasized that the ions are produced in the act of ...
a charge — 2 e. Under the action of the electrical force the hydrogen ions move in the direction of the cathode, they combine with SO4 894 ions, other molecules dissociate, etc.; but, as the current flows, hydrogen ions continuously come up to the cathode, give up their charges, combine with other hydrogen atoms to fo...
is the anode, it dis- solves, and silver is deposited on the cathode. This offers a method of silver plating. In tin; last two illustrations it is seen that the mechanism by which tin- current enters the electrolyte from the anode consists in the copper or the silver plates dissolving; this is done by the positively c...
be applied before electrolysis begins; but its value is dif- ferent for different electrolytes. This may be calculated, however, from a knowledge of the heats of combination of the compounds which are separated by the electrolysis and of their electro-chemical equivalents. Thus, experiments prove that, when 18 g. of w...
OF THE CURRENT 697 parsing off of positive zinc ions into the liquid. The chem- ical action is the solution of the zinc in the acid and the evolution of hydrogen at the copper pole ; and experiments have proved that when 65.4 g. of zinc are dissolved in dilute sulphuric acid, 38,066 calories are evolved. The electro- ...
. Such a combination of elec- trodes and electrolyte is called a "storage cell" or a "secondary cell"; and when it is in a condition to produce a current itself, it is said to be " charged " — but it is evident that this expression has no connec- tion with what has been called a " charge " in pre- vious chapters. FIG. ...
a dark space from a luminous region, and that this is separated by a second dark space from a luminous striated column extending to the anode, the end of which — if it is a wire — has a bright spot of light. The first dark space near the cathode is called the " Crookes dark space " ; the second one, the " Faraday dark...
is receiving a negative charge ; and the fact that, when the rays strike a solid its temperature is raised, is ex- plained by assuming that the rays consist of material parti- cles. Again, as will be shown in a few pages, a charged particle in rapid motion has the same action on a magnet as does an electric current ; ...
to canal rays, and "/3 rays," which are negatively charged particles analogous to cathode rays. Radium also emits rays which are like X-rays in many respects; they are called "7 rays." This radiation is accompanied by changes inside the mole- cules of the substances which emit it ; and in some cases the products of th...
. So tar as is known a moving piece of uncharged matter does not affect the ether; but, it' charged. it does; and. if it> motion has a* • //. waves are produced. It is known from theoretical considerations that when a charged particle U in motion, its kinetic energy is greater than it would he if it were not charged; a...
strength is ev. It is probable that this is true, even if v is very great, much greater than it is possible to attain by any mechanical means. A current due to a moving charge is called a "convection current." CHAPTER XLVI MAGNETIC ACTION OF A CURRENT General Description. — In a previous chapter a general description ...
tte tllf-e. UOD of parallel current*. These phenomena of electro-magnetic forces were discov- 1 by Ampere, and lie invented many most beautiful experi- 710 ELECTRODYNAMICS 999.9 - 9999 merits to illustrate them. They may be found described in many text-books. He also proposed a theory of magnetism based upon his observ...
t, the work done in threading them by a unit pole is, in accordance with the above definition of a unit current, 4 irN x i. So, Rx = 4 TrN x i, or, R = 4 irNi ; a most important formula.. — Magnetic force inside a long solenoid. If there is a rod of iron, of permeability ^, filling the solenoid, the number of tubes of...
around the electro-magnet may be connected to a primary cell or a battery of cells at a distance, with a key in circuit. So, when the key is pressed, a current will flow around the magnet. Even if the current is extremely feeble, the armature will be attracted ; and by means of suitable contact points a sec- ond cell ...
eshoe magnet, between whose poles a coil 0 is supported by means of a vertical wire. The wire in this coil is continu- ous from A to B, two fixed binding screws. When no current is passing, the coil is held so that its plane is parallel to the line joining the two poles ; but if a current is transmitted through the coi...
OF STEADY CURRENTS Steady Current. — In the foregoing chapters the various properties of electric currents, viz., heating, magnetic, < trolytic, etc., have been discussed and illustrated ; and several methods for the production of currents have been described. A current is called u steady " if these properties remain ...
two points of a conductor only if there is a difference in potential between them ; so that we may in a way regard the E. M. F. as the cause of the current, and it is not un- natural, judging from analogy with the flow of heat in a bar owing to difference in temperature between two points, to advance the hypothesis th...
of R for any portion of a uniform con- ductor of constant cross section varies directly as the length of this portion. It, while a constant E. M. F. is maintained between the two points A and B, a second conductor is introduced be- tween them, identical with the first one, each will carry a current i = —, and so the c...
— Let the circuit branch at any point A into two or more conductors which meet again at B; let the resistance of these branches be Rv R2, R& etc. ; and let the currents FIG. 405.— Conductors in parallel. LAWS «/• STEADY friiliBNTS flowing in each be t\. i.2. iy etc. The total current is / = /! -f /2 4- i3 -I- ••• ; an...
adopt the resistance of this conductor as the unit. Thus, the ohm i d. -lined to he t ipial to the resistance of a column of mereui\ 730 KlJX'TltoDY \AMirs at 0° C., of uniform cross section, of length 106.3 cm. and having the mass 14.4521 g. (This column, then, has a cross section of almost exactly 1 sq. mm., accepti...
a conductor with change in temperature offers at once a method of making a "resistance thermometer " ; and, in fact, a " platinum thermometer " con- sisting of a coil of platinum wire whose resistance can be measured is at the present time the most satisfactory ther- mometer in use for accurate work. Similarly, the sa...
Henry observed that if a wire were wound around the soft iron armature of a horseshoe electro-magnet and if the current were suddenly broken, or if the armature were suddenly removed from the magnet, a shock would be felt, if the two ends of the wire were held in the hands ; or, if these ends were joined to a galvanom...
the cir- cuit. If iron is inside the circuit, it is magnetized bv the current ; and thus the induction is changed. (It \\a>, in Fio. 418. - Faraday '» double coll in his first experiment. iiUr to this Study of induced currents that Farada\ Was h-d to his Conception of tubes of induction and to the id.-. i of these tub...
a decrease in the number «.f t ul».-s. the induced current h a direction as to incre<i*> tin- number. In general. then, the induced em-rent produced by any change in the magnetic field throu-h i h a direction as to tend to neutralize this change. ( If this \\.-re n..t true, an increase in AMBS'8 FIIT«ICfl — 47 738 ELE...
(These currents produced in a solid core are called "eddy," or Foucault currents.) A condenser is always in- troduced in the battery circuit in parallel with the " primary " coil A. One of its chief functions is to prevent sparking FIG. 418. — Diagram of induction coil. at the points where the circuit is broken ; it d...
the circuit in- creases, because the circuit will include more tubes. In tin- case of a solenoid which has N turns per unit length, the magnetic force inside has been shown to be 4 irNi ; therefore, it I is the length of the solenoid, each tube of force passes through the current Nl times; and, it.1 is the area of the...
these changes evidently varies directly as L ; so that L measures what may be called the 44 inertia of the current." When the circuit is broken, the energy of the magnetic field is no longer maintained by the cell, and it returns into the conductor, continuing the current until all the energy is consumed in heating th...
and an exact calculation can be made of the effect of all the coils, not simply of those near the middle. If n^ is the total number of turns in the primary, and n2 that in the secondary, the coefficient of self-induction of the primary is proportional to nf ; and the coefficient of mutual induction of the two coils is...

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