With the publication of “Speech and Hearing’ by
Harvey Fletcher, Acoustical Research Director, the
fifth book of the Bell Telephone Laboratories series
comes into being. An introduction to this volume,
contributed by Dr. Arnold, is here reprinted.

HE atmosphere of sounds in
which we live ministers so
constantly to our knowledge
and enjoyment of our surroundings
that through long familiarity we have
come to feel, if not contempt, at least
indifference toward the marvelous
mechanism through which it works.
Hearing, we are inclined to consider
as little a matter for concern as
breathing; and so long as our own
faculty remains unimpaired we feel
little curiosity concerning the provi-
sions of nature either for ourselves
or for others. When we hear too
faintly or indistinctly we know we
need only trace the sound to its source
to hear its perfect form, for that is
the method we have used from child-
hood in investigating the sounds of
our immediate neighborhood.
Now with one broad sweep the
barriers of time and space are gone
and all the world becomes our vocal

neighborhood. No longer can we
transport ourselves to the origin of a
sound and thus become convinced that
we are hearing it aright, for that
origin may be thousands of miles
away or may have vanished years
before; and so we must establish a
new method to measure the accuracy
of the copy which reaches our ears.
We must also find a clearer index to
our satisfaction in it, for we are no
longer concerned with the immutable
provisions of nature but may ap-
proach at corresponding expense
whatever perfection we may demand
in our instruments of translation and
reproduction. Thus the telephone
and the phonograph should excite a
keener interest in how we hear and
in what measures our satisfaction in
the speech and music they provide.
Our ears are only machines to
translate air waves into a form suit-
ed to stimulate the auditory nerve;

and as machines we may measure and
describe them in the same terms that
apply to devices we ourselves con-
struct. We may compare them as to
performance, and may accommodate
our devices to their requirements. But,
to understand the mechanism of the
ear is by no means to understand the
act of hearing, for we have not heard
until the brain has perceived the mes-
sage sent by the auditory nerve. We
cannot explain in precise mechanical
terms how this is done, nor indeed
have we any very clear comprehen-
sion of the process at present. Some
important factors relating to the pro-
cess of hearing we can, however, de-
termine by measuring the least
changes in sound which can be detect-
ed under a variety of conditions of
pitch, loudness, and accompanying
noise. Thus we may obtain a quanti-
tative means of comparing individuals
in this respect, and establish a stand-
ard of average hearing.

There is a most important factor
in hearing, however, which is much
more difficult of analysis and measure-
ment. This is the individual’s ability
to recognize small defects in those
sounds with which he has become es-
pecially familiar. We all know how
quickly we note a slight change in a
friend’s voice, and with what uncanny
skill a trained musician will detect
minute imperfections in very complex
sounds. Our approach to a quantita-
tive understanding of the importance
of this must be by an indirect method.
First we must construct devices so
perfect that even the keenest ear can-
not find a flaw in their rendition, and
then step by step we may introduce
measured imperfections until an ob-
server can detect a fault. In the re-
sponse of individuals to this test there
will, of course, be great differences;

but when we have collated opinions
from a wide variety of observers we
may forecast in a reasonable way the
degree of mechanical perfection that
may be demanded of our instruments.

This, then, has been the philosophy
of the investigation of hearing which
has been carried on in Bell Telephone
Laboratories during the past fifteen
years: to get an accurate physical
description and a measure of the me-
chanical operation of human ears in
such terms that we may relate them
directly to our electrical and acousti-
cal instruments; to test the keenness
of the sound-discriminating sense and
find what is the smallest distortion
which the mind can perceive and how
it reacts to somewhat larger distor-
tions; and thus to reach a reasonable
basis of design both for separate in-
struments and for systems, as a
whole, to give a proper balance be-
tween cost and performance.

With hearing, speech and music
are linked inseparably for they only
bring a meaning through our aural
sense. It is an instinctive first thought
that they must be heard to be criti-
cized. They can, nevertheless, be in-
vestigated by mechanical means and
be described in the same physical
terms that we use in describing hear-
ing; and thus to an extent we may
consider them both objectively. But
if we attempt to divide the study be-
tween speech and music we come at
once upon the difficulty that speech
conveys information by intonation as
well as by articulate syllables; and this
makes it infeasible to set a definite
boundary between them. A division,
however, between vocal sounds and
instrumental sounds proves more use-
ful, for in the one case we are limited
by our vocal organs which we must
take as they are, while in the other

we have a definite control and can
adapt the nature and complexity of
the sounds produced to conform to
our sense of hearing and our musical
appreciation. The investigation of
speech and music has been governed
by these general considerations. An
attempt has been made to establish
in definite terms the performance and
limitation of the voice and, although
so far in considerably less detail, to
find the corresponding factors in in-
strumental music.

With a clear knowledge of the na-
ture of the sounds that we must pro-
duce and the accuracy with which we
must maintain their form, there re-
mains the problem of securing instru-
ments which are sufficiently refined
for the purpose. Instruments of re-
markable precision are required in the
conduct of the investigation, since if
we are to measure the smallest detect-
able variations in sounds we must ob-
viously use equipment which is cap-
able of a degree of exactness beyond
these small quantities. Such instru-
ments would appear at first sight not
to have much utility outside the labo-
ratory, since they are costly and often
complicated and difficult to adjust.

It is interesting to note, however,
that some of the instruments, in es-
sentially their original laboratory
form, have found other important
uses. Indeed, a surprising number of
modern acoustical accomplishments
have come about through the use of
slightly modified forms of the appa-
ratus which was originally developed
for these investigations. Modern

phonographic records are produced
with an electrical transmitter which
was developed in the very early stages
of these studies; and radio broad-
casting has grown up around this
same “microphone.”

ing equipment of the modern phono-
graph and of the radio were predi-
cated directly upon these investiga-
tions; and talking motion-pictures
owe their success and much of their
apparatus to this same source.
Although the results which relate
to normal speech and hearing are nat-
urally the most familiar and widely
known, there have also been import-
ant outgrowths in the way of aids
to those handicapped in one or the
other of these faculties. In establish-
ing the functioning of the average ear
it was obviously necessary to investi-
gate a large number of cases and
among them some which departed
rather widely from the average. For
this study an instrument was devised,
now known as the audiometer, which
has put within the reach of all who
need it the possibility of an accurate
measure of their hearing. In quite
analogous fashion there grew out of
the investigation of the limits of hear-
ing a better knowledge of ways to
provide aids for those partially deaf;
and it has even become possible to
provide means of speech for some
persons whose vocal cords are gone.
Valuable as these results are, eco-
nomically the most important out-
come of the work has been the in-
crease of exact knowledge as to the
requirements and limitations to be
placed upon the transmission of
speech in the telephone system. As
time goes on there must be an evolu-
tion toward even greater perfection
in those particular elements which are
most important to intelligibility. The
system is so large that the cost of
such an evolution is immense and
changes undertaken without an accu-
rate knowledge of their value might
lead to burdensome expenditures for
disproportionate results; but, with the

facts established by this investigation
in hand, we can weigh any contem-
plated change and judge whether it
is the one that offers most improve-
ment at the moment and what its ulti-
mate effect will be in its operation
with other elements of the system.

Crandall and himself, for which since
Doctor Crandall’s death he has had
the full responsibility. No one can
speak with better knowledge of the
facts or with more complete author-
ity for the opinions he expresses.

The work is not complete—indeed
some parts of it are hardly more
than started; yet its results have been
so great, both for the original pur-
pose which was planned and for the
many issues which have since arisen,
that it presents a unique exemplifica-
tion of the worth of systematic and
sustained research; and Doctor
Fletcher is to be congratulated that
he has seen it through with such clear
vision as permits its presentation in
its present form.

BELL TELEPHONE LABORATORIES SERIES
of books published by
D. Van Nostrand and Company

brought the telephone sys-
tem to its present state of usefulness
and efficiency, none, perhaps, is more
typical of steady improvement than
is lead-covered cable. The growth
from the fifty-pair of 1888 to the
1200-pair cable of 1912 has already
been described in the REcorpD.* As
is commonly the case, however, difh-
culties become greater the further a
development is carried. The step
from 1200 to 1800 pairs, taken by
the new development, although it
represents no greater percentage in-
crease in size than many of the pre-
ceding steps, and is even smaller than
some, is a noteworthy
achievement because
with each increase in
the number of pairs,
and each decrease in
size of wire, the difh-
culties of manufacture
become greater.

With the increasing
congestion in metro-
politan areas, avail-
able space beneath the streets —
where cables must be placed — is rap-
idly being used up. Added demands
for power, light, water, transporta-
tion, and other utilities all require
their share of this space. Obtaining
a fifty per cent increase in the number

of telephone wires that may be run
through a duct is thus a real contribu-
tion to the growth and development
of densely populated districts, and
promises further economies in this and
also other situations.

The largest cable existing previous-
ly used twenty-four gauge conductors
wrapped with paper one-quarter inch
wide and two and one-half mils thick,
and its 1212 pairs, so insulated, were
contained within a lead sheath of
about two and five-eighths inches out-
side diameter. Cables of this diameter
are the largest that can be pulled into
many existing ducts, and so this out-
side diameter is one of the limiting
factors of exchange-cable design. The

problem, therefore, is not merely to
make a cable with a greater number
of conductors but to change the de-
sign and methods of manufacture so
that the larger number of wires can
be contained within the same size of
sheath.

Obviously there are two possibil-
ities; either the size of the conductors

or the thickness of the paper insula-
tion may be reduced. There are dif-
ficulties involved in such reductions,
however, both in the manufacture of
the cable and in handling it after its
completion. A cable must be pulled

Fig. 2—In this cross-section of the 1200-
pair cable also the layered construction is
clearly evident

into a duct from one manhole to the
next, and possibly in the course of its
life may be pulled out of one duct
and into another. This pulling sub-
jects the cable to strains and there
is a possibility of breaks resulting in
the conductors if they are too weak.
Besides this the lengths of cable must
be spliced in each manhole and because
of the difficulty of handling smaller
wires they cannot be reduced too far
in size. In addition the factor of re-
sistance can never be overlooked. The
smaller the conductor the higher is
the resistance and the greater, there-
fore, are the transmission losses.

In the course of development, pro-
jected to overcome these difficulties,
many experiments were tried. Wires
of different materials were experi-
mented with to find out whether
tougher substances, such as hard cop-
per or bronze, would not add enough

strength to offset a decrease in size.
Results were not very satisfactory.
The harder wire was springy and dif-
ficult to handle at the splices. Cables
of soft copper but of smaller sizes
were also experimented with and it
was found that wire as small as twen-
ty-seven gauge could be used.

Then, attention had to be given to
the matter of paper. The thickness
used with the 1200-pair cable was
chosen principally for reasons of
strength. In building up the cable the
wires must be crowded together with
considerable pressure and in handling
the cable after completion, particu-
larly in bending it, similar pressures
are developed. If the paper is too

Fig. 3-——A_ cross-section of the 1800-
pair cable shows how the eighteen units
are formed into the final cable

tempting to use paper thinner than
used in the 1200-pair cable another
difficulty arises. In wrapping the
paper strip around the conductor in
the manufacturing process, certain
tension must be maintained and with
too fragile a paper tearing is apt to

result. This difficulty was partly over-
come by the Western Electric Com-
pany through improving its insulating
machinery so that thinner paper could
be satisfactorily used. It was thus
possible to employ paper which was
appreciably thinner than the two-and-
one-half-mil paper of the earlier cable.

While all this work was going on
another development had been made
which changed the arrangement of
the pairs of conductors inside the
sheath. The basic unit of all tele-
phone cables of this type is the pair:
two conductors, each insulated with
paper, twisted together. In _ practi-
cally all the earlier cables these pairs
were laid up in concentric layers.
Each layer was spiraled around the
layer beneath it, and the direction of
the spiral of successive layers was
reversed. This gave a firm body that
could be easily handled.

The new development built up
small unit cables, each of 101 pairs
for the 1818-pair cable, and then as-
sembled these in a long spiral to
form the complete cable. This new
method brought about certain small
savings due to a reduction in the take-
up—or shortening of the effective
length of the conductors due to
stranding—and considerably simpli-
fied the manufacturing of the larger
sizes of cable. It resulted in a more
flexible core which is also important
with the larger cables.

As a result of these various devel-
opments and improvements, an ex-
perimental cable was constructed with
1818 pairs of twenty-seven-gauge wire.
Experiments in pulling this cable in
and out of ducts indicated that a
somewhat firmer core would be desir-
able. A cable of the same number of
pairs but with twenty-six-gauge wire

was then tried and found satisfactory.
It is this cable that has now been
standardized and will be used in the
future in many of the large metro-
politan areas and other places where
conditions make it desirable.

In building up the new cable, two
of the hundred-pair units are used as
a center and around them are spiraled
six other hundred-pair units. Around
these are laid the remaining ten units
to complete the full 1800 pairs. This
may be seen in Figure 4, where the
two inner groups point vertically up-

ward, the next layer of six units
points out at an angle of about forty-
five degrees, and the outer layer of
ten units is bent down.

For convenience in identifying pairs
for splicing, it is customary in all the
larger cables to use several colors of
paper to insulate different groups of
pairs. In the 1200-pair cable, for ex-
ample, the pairs in each group all have
insulation of the same colors, which
are different for adjacent groups. In

all, six colors are used. Each group is green and the other blue-white Paper.
distributed over the whole or part The next layer has one unit of red.

N
— ORANGE BINDER ON EACH
gl UNIT IN OUTER LAYER.
RED- GREEN »
“WHITE BLUE-WHITE
ORANGE-GREEN BINDER
RED-GREEN ON EACH UNIT IN FIRST
LAYER.
RED- / BLUE- BLUE-\
wuHite / WHITE WHITE \ wHiTe
RED-GREEN
ORANGE BINDER ON
BLUE- WHITE v4 EACH UNIT IN CENTER
BLUE- RED- ED- /BLUE-
WHITE \ WHITE WHITE / WHITE [7
UE-WHITE
RED-WHITE RED-wuire
BLUE-WHITE LY
Yo

three red-green groups makes identification of
groups comparatively simple

green, and on each side of it a
blue-white unit, followed by a
red-white unit, and so on. The
outer layer is similarly built
up with one red-green unit and
then alternately blue-white and
red-white units. As a result
the cable is symmetrical in ap-
pearance when looked at from
each end so that locating cor-
responding units in making a
splice in a manhole is a rela-
tively simple matter.

At the termination of these
cables in central offices it is
customary, for convenience in
distributing the pairs to the
main frame, to splice them

of one or more of the annular layers, into several small cables with double
and the same color appears only in — silk and single cotton insulation. In

each group is bunched to-
gether and joined to the
corresponding group of the
continuing cable.

This method is facili-
tated by the new construc-
tion, as the hundred pairs
of a unit are all of the same
color and already bunched.
Each unit in addition is
loosely bound with cotton
threads, those of adjacent
layers being of different
colors, which makes it easier
to identify corresponding
units. A simplification of
the color scheme has been
developed which is indi-
cated in Figure 5. The two
wires of a pair are always
insulated with differently
colored paper and one of

Fig. 6—The fourth cable from the bottom shows
an 1800-pair cable spliced to nine 200-pair cables

Figure 6 is shown such a splice
where nine 200-pair are con-
nected to one of the new 1800-
cables. The 200-pair cables
run under the floor for a few
feet and then up the vertical
side of the frame where they
are fanned out and connected
to terminal protector blocks.
The amount of space required
for fanning out one of the new
cables can be seen in Figure 7.
Each 200-pair cable requires
about five feet of terminal
strip so that nine rows of
blocks, each about five feet
high, are required in all. As
a contrast a small piece of the
1800-pair cable is placed be-
side the terminal blocks.
These last two views were
taken in the Cumberland Of-
fice of the New York Tele-
phone Company in Brooklyn
and show the termination of
the first commercial installa-
tion of 1800-pair cable, which
was completed in the spring
of 1927. Since that time a
limited amount of this cable

Fig. 7—Nine rows of terminal blocks—each
about five feet high—are required to fan out
an 1800-pair cable

has been manufactured on temporar- tion new and improved machinery in
ily modified machinery. The Western order that it may be in a position to
Electric Company, however, has de- take care of the demand that is ex-
‘signed and is about to put into opera- pected for the new product.

CENTRAL office, function-
ally considered, is that part
of a telephone system which

this rapidly growing part of the tele-
phone plant. In some of the larger
cities P. B. X. attendants outnumber
central-ofice operators; in Manhat-

tan, for example, there are about
9500 central-ofhice operators while the
P. B. X. attendants number approxi-
mately twenty thousand.

In the very early days a single tele-
phone in any one residence or place
of business was ample. The telephone
was so superior to former methods
of communication, by mail or mes-
senger, that its easy accessibility to
each individual that might have occa-
sion to use it never occurred to any
one as being at all necessary. Nor
did it seem necessary to have tele-
phonic means of communication be-
tween persons within a single estab-
lishment — much smaller at that time
than are some of our gigantic cor-
porations now. As the telephone
came to be used more and more, how-
ever, and as greater numbers of em-
ployees in every office or factory
found occasion to take advantage of
its time-saving possibilities, a demand
naturally arose for more than one
station in the larger establishments.
There arose also a need for the tele-
phone for intercommunication; a
bookkeeper in the office found much
time and energy could be saved if he
could talk directly with a clerk in the
shipping room. Out of these de-
mands arose the private branch ex-
change, or P. B- X. as it is colloquially
termed, a private central office serv-
ing directly its own stations.

only solution possible. There could
have been the same multiplicity of
stations within the establishment and
the same possibility of intercommuni-
cation, had each station had its own
line to the main central office and its
own number. Any station could have
called another by passing through the
central office operator, and so far as
the members of the organization were
concerned there would have been little
difference except that the station
designation numbers might have been
longer.

From the standpoint of some one
calling in from the outside, however,
there is a considerable difference. The
outsider often does not know the
name of the person he wants to talk
to; he knows what he wants to find
out or what knowledge he wants to
impart but that is all. If for any es-
tablishment there were only a long
list of names and numbers in the di-
rectory he would be helpless. Obvi-
ously the only satisfactory solution

is to have but a single number for
any one establishment and a single
person—or, for the larger concerns,
a single group of persons—to an-
swer all incoming calls. This person,
the P. B. X. attendant, with intimate
knowledge of the organization could
connect the incoming call to the sta-
tion that could most effectively deal
with it. Thus the need for an at-
tendant was paramount in calling the
P.B.X. into existance and the at-
tendant is still of primary importance
to the modern P. B. X. system.

If there are fifty telephone stations
in the local establishment they will
never all want to talk with the outside
simultaneously. At any one time some
stations will not be in use at all and
some may be talking to other local
stations, leaving only a small re-
mainder making demands for outside
service. The ratio of central-office
trunks to stations, therefore, is -al-
ways less than unity although it varies
over a considerable range depending

on the type of business. The at-
tendant and the P.B.X., of course,
always partially, and occasionally en-
tirely, offset the savings due to the
reduction in number of trunks. The
attendant, however, performs so
many useful services that she is gen-
erally regarded as an asset rather
than an expense.

Differences in types of business as
well as differences in size naturally
affect the P. B. X. equipment fur-
nished for the subscriber. In some
organizations most of the calling is
between members within the organi-
zation, whereas in others practically
no local calls are made. In some
places conditions favor dial service
while in others the manual system
offers certain advantages. Differences
in the number of stations to be served
necessarily make a difference in the
type of P. B. X. furnished. Thirty-
five varieties of P. B. X. have been
made in the past and probably more

will be built in the future as methods
of doing business change and as tele-
phone apparatus and equipment im-
prove. ‘There has never been this
number in standard use, however, at
any one time. At present only six
types are standard and stocked and
this number probably fairly repre-
sents the number standardized at any
one time in the past. |

In the manual class the range of
size varies from the small 505 type,
with a maximum of seven stations
and three central-oflice trunks, to the
large 604-C which, as used by the
Consolidated Gas Company of New
York, has 1650 station lines, 221
trunks to central offices, and 175 tie
lines to other branch exchanges, and
requires 42 attendants during the
busy part of the day.

The small 505-type board uses no
cords or plugs but all connections are
made by keys on the front of the
board. It is so small that it can be

placed on an ordinary desk, and may
be operated by a clerk who may also
have other duties. Contrasting with
this the larger exchanges, such as the
one in our own Laboratories, have all
the appearance of a central office.
Between these extremes are other
types and sizes such as the 550* and
the 600-C.

Each type of board is made neces-
sary by the conditions of service that
it has to meet and by the number of
lines that it must serve. The cord-
less 505 type is compact and seems
very simple but actually would become
dificult to operate if the number of
lines were increased to any great ex-
tent. To locate an operated key
from the large number all exactly
alike becomes somewhat trying. A
cord plugged into a jack, on the other
hand, is easy to see and so as the
number of lines increases better re-
sults are secured with cords.

The No. 1 and No. 2 intercom-
municating sets, which do not require
attendants for local calls, are interest-
ing because of their small size. Lines
run from each station to every other,
and each station is in reality its own
P. B. X. as a key is depressed corre-
sponding to the line wanted and no
other switching equipment is required.
Except for this very small unit, pri-
vate branch exchanges not requiring
an attendant for local calls have been
designated for the larger installations
only. The present standards are the
700 and the 740** dial-types, the for-
mer of which may have any capacity
up to one approaching that of a cen-
tral office. Both of these boards may
dial an outside number without the

There is a large and increasing de-
mand for tie-line intercommunication

Fig. 4—Dial-type private branch ex-
changes have usually been made in the
larger sizes as indicated by this section

between P. B. X.’s._ Large organiza-
tions, such as public service companies,
often have anumber of private branch
exchanges located at different points
throughout the city. The tie-lines may
be arranged for dial or manual serv-
ice, depending upon the type of P. B.
X. and the requirements of the sub-
scribers. When tie-lines are provided
between dial P. B. X.’s the circuits can
be arranged, if desired, so that a sta-
tion in one P. B. X. can dial any sta-
tion in another. At Bell Laboratories
there are direct tie-lines to and from
nine other Bell System P. B. X.’s in
and around New York City.

Fig. 5—A P. B. X. of the dial type as arule has a group of manual positions for the
answering of incoming calls. The above is a part of a 700 P. B. X.

Of the 115,000 P. B. X.’s manufac-
tured by the Western Electric Com-
pany during the period from 1910 to
1926, 96% were of the small sizes.
Of these 9% were of the No. 2 and
No. 4 types, the latter of which is now
no longer standard, the other 87%
being about equally divided between
the 505 and the 550 types. Natural-
ly, there are fewer of the very large
boards so it is not surprising that in

this same period only a score or more
of these have been manufactured, al-
though additional sections are being
made continually to take care of the
expansion of the existing boards.
These figures make it easier to under-
stand that in some central offices in
the business section of New York
City approximately seventy-five per
cent of the total working lines termi-
nate in private branch exchanges.

pears to be a similarity between
some of the phenomena observed in
atomic physics and those found in cer-
tain non-linear electrical circuits. This
idea is interesting and very important
since it suggests the possibility of ac-
counting on purely classical grounds
for the methods used in calculating
quantum phenomena. The non-linear
circuits of interest here are of the
variable reactance type such as the
magnetic modulator for variable in-
ductance, and the condenser transmit-
ter for variable capacitance.

A number of years ago some of us
in the Research Laboratory were
working on magnetic modulator cir-
cuits to check theoretical speculations
which were of considerable interest
at that time. All modulators have this
feature in common, that they distort
the wave shape impressed upon them:
a process which yields new frequen-
cies related to those originally im-
pressed on the circuit. If for example
a pure sine-wave generator is con-
nected to the modulator, then the new
frequencies produced are harmonics,
integral multiples, of the generator
frequency. When two of these gen-
erators of different frequency are con-
nected to the modulator (they may
be the carrier and voice waves of the
ordinary radio broadcast transmitter )
we get, in addition to the harmonics
of each of the generator frequencies,

combinations between them, among
which are the sum and the difference
of the two original frequencies. The
latter are known as side frequencies;
they are evidently produced by the
wave-distorting or non-linear prop-
erties of the modulator, since these
new frequencies do not arise when or-
dinary non-distorting elements make
up the circuit. In the magnetic modu-
lator the non-linearity is provided by
the magnetization characteristic when
sufficiently large magnetizing forces
are used.

The problems arising in modulator
circuits are those concerning the re-
lationship of these new current com-
ponents to the original ones. Two of
the properties of the modulator which
are of interest in this connection are
the stability, and the ratio of the side-
frequency power developed to the sig-
nal power supplied; usually the latter
is termed the modulating gain. In
the first magnetic modulator circuit
set up, we had three filters connected
to the modulating coil: one to supply
the carrier, the next to supply the sig-
nal, and the last to take off one of
the side-frequencies to a load circuit.
Even at the most favorable value of
carrier voltage, the modulating gain
was found to be too low with our
hastily improvised arrangement and
we set about the construction of a
more efficient circuit. To do this the
modulator coil was built up with very
thin laminations of permalloy, and

the number of turns and the size of
the coil were adjusted to draw maxi-
mum power from the two connected
generators. When these changes
were gradually incorporated in the
circuit, the modulating gain rose un-
til finally a curious phenomenon was
noticed by E. T. Burton: the circuit
became unstable, and a number of
new frequencies were produced which
apparently bore no relation to the

Circuit for the production of low-
frequency oscillations. Current from the
carrier frequency (p) generator, applied
to the toroidal coil yields simultaneously a
low frequency (q) current and the side-
frequencies. A tuned circuit is provided
for only one side-frequency — the lower

originally impressed frequency. These
were made evident by a mushy note
which was heard when a telephone
receiver was connected in circuit. This
effect obviously set a limit to the gain
which could be usefully obtained and
it seemed desirable to establish the
reasons for its appearance.

The effects are more easily follow-
ed when we use simple tuned circuits
instead of filters. In that case single
frequencies are generated rather than
the large number of frequencies which
appeared in the filter circuit and gave
rise to the mushy note observed. An
approximate mathematical analysis
of this simplified circuit was made.
Assuming a magnetic core free from
hysteresis and working under simple
circuit conditions, it was found that
the flow of the two side-frequencies
changed the coil resistance to the two

input frequencies. In the path of the
higher impressed frequency p this re-
sistance was positive; in the path of
the lower impressed frequency q the
resistance introduced by the flow of
the upper side-frequency was positive
but the resistance introduced by the
flow of the lower side-frequency was
negative. These conclusions were in
complete agreement with those which
had been found theoretically by Mr.
Hartley in 1917, and which he had
also obtained somewhat later in the
case of a condenser transmitter. These
conclusions are carried over un-
changed to the higher order side-
frequencies such as 2p+q and 3p+q.

This idea of negative resistance
enabled us to account for the experi-
mental observation in a qualitative
way at least, and justified the initial
assumption that the non-linear mag-
netic characteristic, and not the
hysteresis loop, was responsible for
the effects. For if the upper side-fre-
quency meets a high circuit imped-
ance, so that the resulting current is
small, and if the lower side-frequency
meets a low circuit impedance, so that
the resulting current is large, then the
net effect of these two currents on the
resistance to q will be negative. When
this net effect, which depends upon
the carrier amplitude, is great enough
to make the total circuit resistance
negative, and when the circuit re-
actances are nearly annulled, then
oscillations will result and if the gen-
erator of frequency q be withdrawn,
this frequency, together with its side-
frequencies, will be sustained. It was
with the simpler circuit shown that
the theoretical conclusions were more
definitely tested and found to be in
general agreement. In order that
sustained frequencies might arise the
carrier was required to exceed a defi-

nite amplitude, the associated circuits
were required to be fairly well tuned
to the two frequencies involved and
the resistances of the tuned circuits
were required to be sufficiently small.
In a circuit using filters these condi-
tions are obeyed at a number of fre-
quencies so that several currents are
sustained.

To sum up these effects we may em-
ploy terms ordinarily used of regen-
erative vacuum-tube circuits, in which
oscillation is produced by feeding
current from the plate to the grid
circuit in proper phase. The source
of energy here is the plate battery,
whereas in the magnetic modulator it
is the carrier generator. For each,
there is a critical value below which
sustained oscillations cannot exist.
Further, in the magnetic modulator
case there is not merely one sustained
oscillation, but at least two, which we
have designated q and p-qg. Neither
can be sustained without the other,
and if we introduce sufficient resis-
tance to either g or p-q, or if we in-
troduce sufficient reactance to either
circuit both oscillations cease.

Mr. Hartley has suggested in a
paper presented before the American
Physical Society on December 29,
1928 that there is a striking resem-
blance between the phenomenon just
described and the Raman effect in
atomic physics. Raman found that
in passing light of a definite spectral
composition through certain liquids,
the spectral composition of the emerg-
ing light was changed. New lines
appeared, sometimes as pairs equally
spaced above and below a line in the
spectrum of the incident light, with
the higher frequency line always
weaker than the lower. In some cases
only the lower frequency line was

strong enough to be observed. Fur-
ther, the interval between the new
lines and the original lines from which
they were displaced has been asso-
ciated with a line in the absorp-
tion spectrum of the liquid; that is,
the interval has been associated with
a molecular resonance. To press the
analogy with the modulator circuit,
the frequency of the incident light
corresponds to the supply frequency
p, the molecular resonance frequency
is q, the stronger observed line is the
lower side-frequency p-g, and the
weaker is the upper side-frequency
p+q. The parallel is even more strik-
ing in the case of the condenser trans-
mitter, in which the same type of ef-
fect occurs, and in which, moreover,
the power involved is proportional
to the frequency. This is suggestive
of the quantum relation.

The importance of Mr. Hartley’s
suggestion lies not only in its applica-
tion to the Raman effect but also in
its application to the general field of
atomic physics. The present effort in
atomic physics is devoted to discover-
ing methods such as matrix mechanics
by which the observed effects may be
computed, and the results are in many
cases in excellent agreement with the
facts. However, there does exist
some question as to the physical sig-
nificance of the quantities employed
in these non-classical methods of com-
putation. Following Mr. Hartley’s
suggestion it may be possible to com-
pute these effects by treating non-
linear mechanisms by ordinary mathe-
matical means. If this should prove
feasible a physical interpretation
would be provided for quantum me-
chanics, and we should then have a
classical mechanism capable of repro-
ducing quantum phenomena.

HARRY PRESCOTT CHARLESWORTH
Entered American Telephone and Telegraph Company, Engineering Department,
1905; Equipment and Transmission Engineer, 1919; Plant Engineer, 19203
Vice-President Bell Telephone Laboratories, 1928

was elected Vice-President
of the Laboratories. He will be in
charge of its operations during Mr.
Craft’s absence.

After graduation by the Massa-
chusetts Institute of Technology in
1905, Mr. Charlesworth entered the
Engineering Department of the
American Telephone and Telegraph
Company, which was then located in
Boston, and in connection with which
one of the development and research
laboratories of the Bell System was
operated.

His first assignment was to the de-
velopment of local and toll circuits
and associated apparatus. In this
work he was engaged for two years,
until in 1907 the American Company
moved to New York City.

During the next ten years Mr.
Charlesworth was active in the de-
velopment of toll operating methods
and the general related engineering
problems involved in extending and
improving telephone service.

With the opening of the war he
was specially assigned, as a result of
his broad knowledge of telephone
plant and its operations, to handle
problems wherein the Bell System
could be of assistance to the Govern-
ment in the national emergency. In
this capacity he was throughout the
war active on communication facili-
ties for army camps, naval bases,
supply depots and particularly for

the Government Departments at
Washington, where he also rendered
continuous assistance to the Tele-
phone Company on general equip-
ment and trafic engineering matters.

At the close of the war he took up
dial-system development work and
with the creation of the Department
of Operation and Engineering, was
appointed Equipment: and Transmis-
sion [ingineer under Vice-President
Gherardi. A year later he became
Plant Engineer of that Department,
in which position he has been con-
cerned with all phases of the engi-
neering of the telephone plant and
with relations with other wire-using
companies.

Thus, throughout his telephone
career of almost a quarter of a cen-
tury, Mr. Charlesworth has taken an
active interest in the development of
telephone apparatus and equipment
to meet telephone needs, and in the
origination of proper operating meth-
ods for handling telephone traffic.
His background of scientific training
and long contact with the develop-
ment and operating problems, and his
proven ability to coordinate and ad-
vance the work of others, have re-
sulted in constantly increasing respon-
sibilities in the Bell System. And now
with an experience well rounded by
his supervision of plant engineering
in general, he returns to his original
interest in development by assuming
leadership of the Bell Telephone
Laboratories.

subscriber’s line. It made the
first of a series of successive selections
resulting in a connection to the line
called. Selectors, however, are com-
paratively expensive mechanisms, and
as they are in use only when the line
is making an outward call a much
smaller number of them would meet
the requirements could some method
be devised of connecting them to a
line only while an outward call was
being made. To the search for the
most efficient method of doing this,
much thought has been given and
many studies made which, embodying
themselves in laboratory development,
have resulted in the step-by-step line

troduction of the Keith or plunger.
type line switch in 1907. This is a
comparatively inexpensive switch one
of which is connected to each subscrib- —
er’s line. It starts operating as the
subscriber lifts the receiver from the
hook and completes a connection to
one of a group of ten trunks leading
to selectors before dialing is begun.
Line switches of a large number of
lines (the exact number being depen-
dent on traffic conditions) have ac-
cess to the same group of ten trunks
with the result that the number of
selectors is much smaller than the
total number of lines.

The possible reduction in selectors
depends for the most part on the num-
ber that may be reached by any one
line, or conversely, on
the number of lines

Fig. 1—Diagrammatic representation of the advantages
from greater mutuality between selectors and lines

finder. Although the mechanism it-
self is of the step-by-step type, the
function it performs owes its incep-
tion to the panel system, a later de-
velopment of the dial-system method
of telephone switching.

vice is fixed by the
number of calls be-
ing placed at one
time but only if each
selector had access to
all the lines could this lower limit be
reached. With a lesser degree of
accessibility the chance distribution of
calls enters to require a greater
number.

Consider for example a small cen-
tral-ofice of one thousand lines over
which a maximum of seventy outgo-

ing calls are made at any one time.
As an initial assumption let each se-
lector have access to twenty lines so
that the thousand lines in the office
may be divided into fifty groups of
twenty lines, each group being served
by a certain number of selectors. The
seventy outgoing calls being made sim-
ultaneously will not, of course, be
equally divided among these groups.
Chance affects the distribution so that
some groups will have more and
others less than the average number.
A possible distribution is indicated on
Figure 1 in numbers written under
each group. With this distribution and
assuming that the number of selec-
tors is to be so chosen that all outgo-
ing calls can be handled immediately,
there must be—-in the case given—
five selectors serving each group as
that is the maximum number of calls
occurring at the same time in any one
group. [he minimum number of se-
lectors possible—seventy for the
thousand lines if there were complete
accessibility — is seven per cent of the
number of lines while with the ar-
rangement indicated, where each se-
lector has access to only twenty lines,
the selectors are twenty-five per cent
of the number of lines.

In grouping lines an effort is always
made to obtain a balance by so sorting
the lines with lower or higher calling
rates among the groups, that the aver-
age and peak calling rate for all
groups is the same. Over a period of
time, therefore, all groups will have
had at one time or another the same
number of simultaneous calls. The
diversity indicated on Figure 1 is only
that existing at any one moment. A
few minutes later the grouping prob-
ably would be entirely different, with
a group now having no calls perhaps
then having five, and this shifting of

Increasing the accessibility by mak-
ing each set include one hundred lines,
indicated by the brackets on the dia-

gram, reduces the ratio of selectors
to lines to twelve per cent. If the in-
crease of accessibility is carried to two
hundred lines the ratio of selectors to
lines may be lowered to ten per cent.
The actual possible decrease in selec-

derived from somewhat intricate
probability calculations based on such
assumptions as the average duration
of a call, and the calling rate, and
probably would not, in any particular
case, fit the figures given in the illus-
tration. These are arbitrarily picked
merely to bring out the possible reduc-

cent, but the use of a line switch hunt-
ing over five trunks to selectors would
reduce this figure, for example given
in Figure 1, to twenty-five per cent.
In this case a group of twenty lines
would be arranged to be served by
five selectors.

tion in selectors due to the effect of
chance distribution and greater acces-
sibility.

In this example only the matter of
mutual accessibility has been men-
tioned; the method of obtaining this
accessibility in practice has not been
brought in. Actually there are two
methods in general use as has already
been indicated: by line switches, or by
line finders. It was natural that the
line switch should have been devel-
oped first because it accomplished a
considerable reduction in the number
of selectors with a simple mechanism
and a minimum number of terminals
over which hunting would have to be
done. Without either line switches
or line finders the ratio of selectors to
lines is, of course, one hundred per

ing the line switches so that they can
hunt over a greater number of trunks.
Based on the data of Figure 1, a line
switch hunting over nineteen trunks
would reduce the ratio of selectors to
lines to nine and one-half per cent.
The line switch method of obtaining
accessibility, however, becomes ex-
pensive when it is attempted to obtain
a large degree of accessibility. A
switch is required for each line and
every increase made in the number of
trunks over which the switch will hunt
means an increased cost which is mul-
tiplied by the number of lines. De-
velopment in the Bell System has been
along the line of the alternative meth-
od of obtaining accessibility by use of
a line finder. With this method the
finding process is reversed; instead of

‘ | >
j |
SWITCHING | SWITCHING SWITCHING | SWITCHING SWITCHING | SWITCHIN | SWITCHING __|_ SWITCHING
RELAY RELAY RELAY RELAY RELAY RELAY

having the lines hunt for an idle selec-
tor, the selectors are made to search
for the calling line. A line finder is
provided for each selector so that
each reduction in the number of selec-
tors brings a like reduction in the
number of line finders. This proves
to be a more satisfactory way, from
an operating standpoint, of solving
the problem.

To obtain the same reduction in se-
lectors, however, the wipers of a line
finder must have access to many more
contacts than those of the line
switches. When the ratio of selectors
to lines is twenty-five per cent, for ex-
ample, each of the 250 line finders
would require access to twenty lines
whereas had line switches been used
each of the thousand would have re-
quired access to only five trunks to
selectors. It is desirable to have the
hunting done between the instant the
receiver is lifted from the hook and
the time the subscriber is ready to
dial so that the difficulty is not so
much in actually hunting over a larger
number of contacts as in accomplish-
ing it in this short time. The manner
in which this rather difficult feat is

As a basis for the step-by-step line
finder there was available the stand-
ard step-by-step mechanism out of
which the selectors and connectors are
made. Its contacts are arranged in
two banks, each having ten levels with
ten contact positions arranged around
a section of circular arc. A pair of
wipers for each bank, by suitable re-
lays and mechanisms, can be moved
up one level at a time and then ro-
tated around the arc to any one of
the ten positions. The movement is
always step-by-step, that is, up one
level at a time or around one contact
position at a time, which gives the
name to the complete system of
switching.

As it was originally used this switch
had access to one hundred lines. Four
contacts were available for each line,
the two banks each of one hundred
pairs of contacts just making up this
number. In the more recent systems
each line requires only three contacts
so that by adding a third bank to the
switch six hundred contacts, or two
hundred lines, become available. An

COMMUT) COMMUTA’ COMMUTATOR COMMUTATOR
;
~~
“Oo
<a <a < <a
| LINE FINDER 2 LINE FINDER | LINE FINDER | LINE 2 o INE FINDER | LINE FINDER 2
WIRE SUB-GROU |suB-GRouP’
| RELAY . | RELAY ' | | RELAY
START
ADVANCE RELAYS ADVANCE RELAYS —- ADVANCE RELAYS ADVANCE RELAYS |
TO SuUB-
START WIRE GROUP 9

THE GROUP RELAYS ARE CONTROLLED BY THE LINE CIRCUHS OF THE HOME LINES WHICH ARE SHOWN IN THE FIRST

Fig. 4—Schematic arrangement of sub-group relays, commutators, and start wires

Fig. 5—Line-finder frames in a central office. Each group of two hundred lines
has only sixteen line finders associated with it

accessibility of two hundred lines was
deemed sufficient to reduce the num-
ber of selectors to a satisfactory total
and the switch thus developed is
shown in Figure 2.

Although this switch gives access
to two hundred lines there are only
one hundred stopping positions of the
brush, ten rotational positions on each
of the ten levels. Which line is chosen
of the two that terminate in each po-
sition depends on the action of relays
associated with the switch. If one of
the pair of lines running to a brush
position were in use and a call should
come in on the other, another of the
finders serving that group would
“hunt” for it, as the two hundred lines
running to any finder are multipled
to each of the other finders serving
that particular two hundred lines.

each group of two hundred lines is
divided into ten sub-groups of twenty
lines, and each of these sub-groups
appears on the lowest level of one or
more of the line-finder banks, and
constitutes the “home lines” for these
finders. ‘This same sub-group of lines
appears in the second level of another
set of line finders, in the third level
of another set, and so on. The line
finder “start” circuit is so arranged
that when a call originates, one of the
line finders that has the calling line
among its “home lines’’ begins to hunt
for it. If these particular finders were
busy the start lead would be trans-

ing line in their second level, and if
these in turn were busy, to the finders
with the line in their third level, and
soon. In this way minimum hunting
time is required for each call. The
manner in which the lines are mul-

tipled to the different finders and the
way in which the start lead is trans-
ferred from one to another may be
understood by a study of Figures 3
and 4.

These two-hundred-point line find-
ers, a typical installation of which is
shown in Figure 5, have now been in
use for some time. In the installa-
tion illustrated, three groups of find-
ers, each group serving two hundred
lines, are mounted in a vertical frame.

NE of the telegraph systems
being used to a steadily in-
creasing degree on Bell Sys-

essary apparatus is now available, re-
taining the electrical characteristics
of the older assembly but introducing
an improvement in compactness and
convenience.

By the use of carrier currents in a
frequency range approximating that
of the voice currents of telephone con-
versations, the system has been made
suitable for a toll plant designed
primarily for telephone transmission.
At intermediate points the complex
current conveying all the telegraph
messages is amplified by ordinary

Carrier-telegraph apparatus for a single wo-way channel, connected to a toll line

four-wire telephone repeaters. The
essential elements of the system are
a generator for producing the carrier
currents; relays for controlling their
transmission in accordance with a
telegraph code; filters for separating
the different frequencies, combined
for transmission over the line; and
vacuum-tubes for rectifying each of
the separated alternating currents
into direct current for operating the
telegraph receiving apparatus. Ter-
minal apparatus embodying these

units, connected at each end of a toll
line, make it a path for telegraph
messages rather than for conversa-
tions.

In the schematic the circuit ar-
rangement is shown. Operation of a
subscriber’s key, or automatic trans-
mitter, controls direct current through
the windings of the sending relay,
which in turn controls the alternating
current passing onto the line. During
spacing signals this relay short-cir-
cuits the alternating current, and dur-
ing marking signals allows it to flow
through the sending filter to the line.
At the incoming end, the receiving fil-
ter of each channel terminal selects
the proper current, which is amplified
and rectified by the vacuum tubes of
the detector circuit. The rectified
current operates the receiving relay,
which in turn controls the receiving
subscriber’s sounder or printer.

be sent as desired, but not simultane-
ously, only one circuit is required be-
tween the subscriber’s premises and
the toll office, but a one-way carrier
channel is needed in each direction.
An important operating feature of
the terminal equipment is the provi-
sion made for monitoring. An atten-
dant at the central office must be able
to observe operation of the circuits to
be sure that everything is in good
order, and must communicate with
the subscribers’ operators from time
to time, in emergencies as well as
about routine matters. The circuit
sketch shows the sounders and meters
by which operation can be observed,
and the telegraph key by which the
attendant can take control of the cir-
cuit. It is important that the monitor-
ing apparatus be as convenient as pos-
sible, since many of the telegraph
channels are used by financial houses
in whose service intérruptions or de-
lays might be costly. Following then-
current telegraph practice, the orig-
inal voice-frequency equipment had
monitoring apparatus permanently
connected to each channel terminal,
although it was not possible for the
attendants to give their oversight to
more than a few repeaters at a time.
Since experience has shown that ade-
quate supervision can be maintained
with fewer sets of monitoring ap-
paratus, in the new form of equip-
ment only one set has been provided
for each four channel terminals.
This use of common monitoring
equipment, connected into any circuit
at will by jacks, plugs and cords, has
been greatly facilitated by the con-
venient location of the apparatus in-
volved. It will be noted from the
photographs that like pieces of ap-
paratus have been grouped on mount-
ing plates especially designed for

them. At the top of each bay are
plates bearing retardation coils, con-
densers, resistances and other minor
elements normally requiring no atten-
tion; the telegraph relays, which need
occasional maintenance, are located
near the bottom; and the central por-
tion of the bay is left clear for the
apparatus used in controlling the re-
peaters. An improvement is thus real-
ized over the method of mounting
both fixed and adjustable apparatus
for a particular circuit on one panel,

Fig. 2—Two bays of panel-mounted
terminal equipment, equivalent to a single
bay new equipment

which of course could not be located
at the most convenient part of the bay
for all the circuits.

Mounting most of the apparatus
on standard mounting plates has
made the bay rather than the panel

graph relays and the receiving po.
tentiometers, there are exactly four
units of apparatus, one for each of
the channel terminals. Where there
are several units for each circuit on
one of the plates, as in the case of the

the unit of equipment. Apparatus for
four channel terminals and one mon-
itoring panel are normally assembled
on a channel-iron rack, and are wired
in a single local cable. In contrast,
the older panel-mounted equipment
required a complete bay for two chan-
nel terminals and the two monitor-
ing panels associated with them. On
many of the mounting plates in the
new bays, such as those for the tele-

resistances and keys, these have been
arranged in four separate groups.
The only exception to the sub-group-
ing on the mounting plates, aside
from the monitoring panel, is the fil-
ters; each of these is assembled com-
plete on an individual plate. As a re-
sult the bay is divided in a general
way into four vertical groups, each
constituting a channel terminal. Or-

groups of three, the number required
for twelve channels in each direction.

The advantages of this type of
mounting are apparent in Figure 1.
Any particular piece of apparatus is
located in the same position in the
bay for every repeater, a feature es-
pecially important for the circuit ele-
ments requiring attention—the jacks,
keys and potentiometers. Convenience
also follows on the wiring side of the
bays from the arrangement, as well
as from the accessibility of the ter-
minals of all the apparatus.

Along with the improved assembly,
simpler types of apparatus have been
introduced. In the older terminal re-
peater, an expensive forty-step rheo-
stat was used for the variable resis-
tance in series with the subscriber’s
loop. This has been replaced by a
series of flat-type resistances having
values of fifty ohms, one hundred
ohms, two hundred ohms, and so on
up to eight hundred ohms, each of
which can be short-circuited by a
push-button key. Any value of resis-
tance from fifty ohms to the total can
be secured, in steps of fifty ohms, by
operation of the proper combination
of keys, with five or six resistances
taking the place of the forty used in

In the Bell System plant, voice-fre-
quency telegraph systems are in use
along the main toll cables, with a to-
tal of about 170,000 miles of two-
way channels in operation on October
I, 1928. There were at that time
thirty-three systems in service, the
longest being from New York to Chi-
cago, a distance of 884 miles. These
systems form a network together with
the open-wire high-frequency tele-
graph systems, which touches almost
every important city in the country,
and is an important factor in main-
taining the highest grade of telegraph
service now offered — telephone type-
writer service at sixty words per min-
ute in each direction. Combining the
advantages of reliability and simplic-
ity with savings in first cost and floor
space, the new equipment will pro-
mote further the use of such facilities,
thereby helping to secure the most
productive use of the toll cables.

problem of an econom-
ical source of ringing current
for the smaller common-bat-

ringing machine of such a capacity
that it will take its place between the
two types already in use. In one
type of these present machines, used
principally in the smallest offices and
in private branch exchanges, battery
current is converted into alternating
current for ringing by a vibrating-
reed interrupter and a transformer.
Although this apparatus is satisfac-
tory at the switchboards for which it
is intended, by its nature it does not
regulate voltage closely enough for
offices presenting a greater variety of
ringing conditions. It is intended for
switchboards at which ringing is con-
trolled manually and at which busy
signals and other information are
given by voice, rather than by signal
tone. No provision is made, there-
fore, for intermittent current for ma-
chine ringing, or for signal tones.
Where requirements call for inter-
rupted currents and tones for sig-
nalling, and for ringing current con-
trolled by the machine rather than
by the operators, a ringing machine
of the other type — Type P — has
been used. In this, a motor driven
alternator furnishes twenty- -cycle volt-
age and rotating drums interrupt the
ringing and signalling currents as re-
quired. The capacities of these ma-
chines, ranging from one to eight am-

peres, make them adequate for the
largest offices, and their output volt-
age and frequency, which are con-
trolled by regulators, are sufficiently
close for the most severe conditions.
For the smaller offices using machine
ringing, however, certain of the prop-
erties of these ringing generators
have not been needed. Regulation is
considerably closer than is necessary
in many such offices, and the current
output of the smallest Type P ma-
chine exceeds requirements of maxi-
mum traffic by a substantial margin.

The new machines have therefore
been designed to embody only those
features useful in offices with a busy-
hour trafic of three thousand calls
or less. A small twenty-cycle motor-
generator set was selected, and high-
speed interrupters were added for
busy and other tones, a commutator
for pulsating current, and low-speed
interrupters to make possible the con-
nections needed for machine ringing.
The generator has a capacity of a
half ampere, delivered at 72 to 88
volts. No voltage regulator on the
output has been provided. In the case
of the battery-driven sets for which
the input voltage may vary between
twenty and twenty-eight, a centri-
fugal regulator has been provided to
hold the speed between 1100 and
1200 revolutions per minute. The
generator voltage is held within suf-
ficiently close limits by additional
field windings in series with the mo-

tor armature. Neither the regulator
nor the compound winding will be
required for machines to be driven
by central-station power.

On the generator shaft are two
slip-rings and a ring for delivering
pulsating current. Tones of 480 and
160 interruptions per second are se-
cured by a brass drum on an extension
of the generator shaft;
one brush feeds direct
current to the drum,
and two pairs of col-
lecting brushes pick up
the interrupted cur-
rents. The low-speed
interrupter, at the end
of the machine, is
driven by a worm-gear.
Instead of another
drum with intermittent
insulated areas in the
path of the brushes,
there is a group of ro-
tating discs which bear
rollers near their circumferences.
During rotation each set of rollers
operates a group of flat contact
springs, similar to the spring pileup
of a key or a relay, which make and
break contact 60 or 120 times per
minute for signalling current, or con-
nect and disconnect ringing current at
the standard ringing intervals. No
provision has been made for current
to collect and return coins, but that
can be supplied readily in these small
offices, by a bank of dry cells or other-
wise.

is also used when the voltage is near
the lower limit to step it up for test-
ing the tripping relays. When the
voltage rises, a relay switches the
testing circuit to the generator ter-
minals.

The whole set, except for the trans-
former, is mounted on a slate slab
which in turn is screwed onto a

The new ringing machine, mounted on its slate and wood
base. The motor-speed regulator is at the extreme right

wooden base. One machine is ade-
quate in capacity, but two will ordi-
narily be provided to insure continu-
ous service. The light weight and
compactness of the sets make it pos-
sible to mount them on a pipe frame-
work, one above the other; the floor
space needed is thus reduced to less
than half of that occupied by two
type P ringing machines.

Economy is not restricted to floor
space, however; two of the sets cost
less than half as much as two of the
type P sets which would otherwise be
needed for an office. The resulting
reduction in the power-plant cost will
have a tendency to extend the appli-
cation of machine ringing in the
smaller offices.

Members of the Laboratories are
naturally attentive to civic enterprises
affecting the convenience of trans-
portation to and from 463 West
Street and the appearance of its en-
virons. West-side improvement pro-
jects have been under discussion for
some time and have taken many
forms. The Board of Estimate of the
City of New York has recently ap-
proved plans for an elevated express
motor highway along the west side
of the city.

The highway will extend from
Canal Street to Seventy-second Street.
Consisting of two roadways, each
thirty feet in width, it will provide
for three lines of traffic in each direc-
tion. Sets of ramps about a mile
apart will furnish access to the high-
way at points other than its termini.
Four ramps with ten-foot roadways
will compose each set, affording as-
cent and descent to uptown and down-
town trafic. From Canal Street to
Fifty-ninth Street the highway will be

supported on sets of three columns.
The sets will be about sixty feet
apart, except where the highway
spans cross-streets, and the columns
of each will be thirty-four feet apart.

Proceeding along West Street, the
highway will pass about seventy feet
west of the front of our building.
The nearest set of ramps will be
somewhat south of Twenty-third
Street; the picture above shows the
anticipated highway at that point.
Ending conveniently near the Holland
Tunnel, and connecting with the Hud-
son River Bridge, the highway will
yet further facilitate automobile pas-
sage between the Laboratories and
New Jersey.

-The section from Canal Street to
Fifty-ninth Street will cost about $16,-
000,000 and will be financed by assess-
ment on the taxpayers of the Bor-
ough of Manhattan. It is expected
that work on this section will begin
in a month or two and will continue
for about three years.

Service Honors for 1928 .
MORE THAN THIRTY YEARS a
Arthur E. Peterson Wilton L. Richards Arnold S. Bertels
Research Department Consulting Historian Systems Development a
Thirty-five years Fifty years Forty years =)
|
Conrad Schaul John F. Toomey a
Development Shop Systems Development - ;
Thirty-five years Thirty-five years -
{249}
} 4
|

Adolph Bregartner Frederick E, Anderson
Systems Development Systems Development

Goodwin Rosenblum Albert J. Ketschke William McA. Smith
Development Shop Research Department Systems Development

Edward J. Harrington George Thompson
Development Shop Systems Development

Adolph Sulzmann Charles Borgmann George Hatcher
Research Department Manual Equipment Engineer Plant Operation

George Hess Sergius P. Grace
Plant Construction Assistant Vice-Presidert

Arthur K. Forsyth George Dodd
Apparatus Development Apparatus Development

George F. Morrison Charles H. Klein
Power Engineer Apparatus Development
Plant Operation

Dr. JEWETT attended an assembly
luncheon of the Boston Chamber of
Commerce at Boston on January 10
and spoke on “The Romance of Re-
search in the Telephone Industry.”

ON DECEMBER 29, Dr. Jewett con-
tributed to a symposium on the “‘Or-
ganization of Scientific Research in
Industry”, at a meeting of the Ameri-
can Association for the Advancement
of Science. His subject was ‘Finding
and Encouragement of Competent
Men.”

J. E. Moravec has been appointed
Assistant Vice-President in charge of
Staff Department, effective January
14. His organization is as follows:
J. W. Farrell, Secretary and General
Attorney, in charge of the Legal De-
partment; W. B. Wallace, Treasurer,
in charge of the Financial Depart-
ment; E. J. Santry, General Audi-
tor, in charge of General Accounting
Department; B. B. Webb, Commer-
cial Relations Manager, in charge of
Commercial Relations Department;
J. S. Hartnett, General Service Man-
ager, in charge of the General Ser-
vice Department; W. B. Sanford,
Plant and Shops Manager, in charge
of Plant and Shops Department.

R. B. Bonney, Educational Direc-
tor of the Mountain States Telephone
and Telegraph Company, was a guest
of the Laboratories January 2 to 16
for an extended inspection of the fac-
ilities here and for observation of
current developments. On account of
his interest in college relations work,
he wanted, among other objectives,

a general picture of the Laboratories
as a research organization, and in-
formation on studies now in progress.

AT THE JANUARY 7 MEETING of
the Colloquium, J. A. Becker spoke
Science of Coated Fila-

ments”. On January 21, J. E. Harris
spoke on ‘“‘Application of the Phase
Rule to Metallurgical Problems’.
Tue AcousTiCAL SOCIETY OF
AMERICA was formed at a meeting
held here on December 27, for the
purpose of bringing together workers
in all branches of pure and applied
acoustics. Among its activities will
be the provision of a medium of pub-
lication for papers on acoustics, for

which there is acute need; such papers
have hitherto been widely scattered.

Elected to temporary office were:
President—Harvey Fletcher of the
Laboratories; Vice-President—Pro-
fessor V. O. Knudsen of the Univer-
sity of California; Secretary— Wal-
lace Waterfall of the Celotex Com-
pany; Treasurer—C. F. Stoddard of
the American Piano Company. A
committee was appointed by Dr.
Fletcher to consider the details of or-
ganization, and the first regular meet-
ing will take place here some time
in April. There were present forty

of the leading authorities on acous.
tics, among whom were Professor D.
C. Miller of the Case School of Ap-
plied Science, Professor F. A. Saun.
ders of Harvard University, J. P.
Maxfield of the Victor Talking Ma.
chine Company, R. V. Parsons of the
Johns Manville Company, and Pro.
fessor F. R. Watson of the Univer.
sity of Illinois. After the meeting,
Dr. Arnold entertained the members
at luncheon.

Members of the Acoustical Society of America: left to right: back row: W. P.
Mason, B.T.L.; J. C. Steinberg, B.T.L.; V. L. Chrisler, Bureau of Standards;
E. J. Schroeter, Macoustic Eng. Co.; E. C. Wente, B.T.L.; W. C. Jones, B.T.L.;
second row from back: L. J. Sivian, B.T.L.; E. L. Norton, B.T.L.; W. A.
MacNair, Victor Co.; R. F. Mallina, Victor Co.; Lonsdale Green, Jr., Johns-
Manville Corp.; R. H. Schroeter, Macoustic Eng. Co.; H. W. Lamson, Gen. Radio
Co.; C. N. Hickman, American Piano Co.; D. G. Blattner, B.T.L.; second
row from front: H. A. Erf, Northern Ohio Tel. Co.; H. C. Harrison, B.T.L.;
J. B. Kelly, B.T.L.; R. L. Wegel, B.7.L.; H. A. Frederick, B.T.L.; N. &.
French, A. T. & T.; C. W. Hewlett, G. E. Co.; A. T. Jones, Smith College;
Irving Wolff, R.C.A.; J. B. Taylor, G. E. Co.; front row: F. A. Saunders,
Harvard U.; R. V. Parsons, Johns-Manville Corp.; D.C. Miller, Case School of
Applied Science; Wallace Waterfall, Celotex Co.; V. O. Knudsen, U. of Cali-
fornia; H. Fletcher, B.T.L.; C. F. Stoddard, American Piano Co.; J. P. Maxfield,
Victor Co.; F. R. Watson, U. of Illinois; F. K. Richtmeyer, Cornell U.;
G. R. Anderson, U. of Toronto

Field Engineer, visited Seattle, Ta-
coma, Portland and other cities in
Washington and Oregon during the
second week in December in connec-
tion with Field Engineering duties.

A. F. GILSON AND P. S. OLMSTEAD
attended a regular survey conference
on telephone receivers at Hawthorne
during the latter part of December.

W. A. Boyp, in company with a
committee for the study of protective
metal finishes, visited Norfolk, At-
lanta, Birmingham and New Orleans
during the early part of January.

A. G. DALTON AND R. J. Nossa-
MAN visited Philadelphia during the
latter part of December in connection
with Field Engineering work.

H. F. DopceE was the author of an
article ‘Using Inspection Data to
Control Quality”, which appeared in
MANUFACTURING INDUSTRIES for
November and December.

E. F. Kincspury addressed the
Women’s Club of Rutherford, New
Jersey, on television on January 7.

AMONG PAPERS presented before
the American Physical Society at its
midwinter meeting at Columbia Uni-
versity were “The Maximum Excur-
sion of the Photoelectric Long Wave
Limit of the Alkali Metals”, by H.
E. Ives, read on December 27, and
“A Wave Mechanism of Quantum
Phenomena” by R. V. L. Hartley, on
December 29. On the latter date, a
paper “Anomalous Dispersion of
Electron Waves by Nickel”, by C. J.
Davisson and L. H. Germer, was also
given.

T. C. Fry was one of the presiding
oficers of a joint meeting of the
Mathematical and Physical Societies.

Research Council on “Substitutes for
Sound” at St. Louis on December 8.
GEORGE KNaAP?P gave an illustrated
talk on television at the Columbian
Club at Elizabeth, New Jersey.

G. R. YENZER was at Hawthorne
on December 10 in connection with
resistance requirements for condenser
transmitters.

R. M. Burns inspected some in-
stances of corrosion in central offices
at Atlantic City on December 3 and 4.

B. L. CLARKE made a survey of
lubrication problems at Hawthorne
and visited centers of lubrication re-
search at Washington, Minneapolis,
Madison and Pittsburgh.

C. L. HipPpeNsTEEL C. W.
BORGMANN discussed corrosion prob-
lems with engineers of the New Jer-
sey Zinc Company at Palmerton,
Pennsylvania.

A. R. Kemp visited the Columbian
Rope Company at Auburn, New
York, in regard to cable develop-
ments.

R. L. PEEK attended the Plasticity
Symposium held at Lafayette College
in Easton, Pennsylvania.

R. M. Burns anv D. J. SALLEY
attended the Soil Corrosion Confer-
ence at the Bureau of Standards at
Washington and made experimental
investigation of protective coatings at
Hawthorne, from December 9 to 29.

HARVEY FLETCHER attended com-
mittee meetings on research for the
deaf at Washington, D. C., in connec-
tion with the Anthropology and Psy-
chology Division of the National Re-
search Council.

R. O. MERCNER visited the Vibra-
tion Specialty Company at Phila-
delphia on December 15 to observe
the balancing of high-speed machines.

E. C. WENTE’s article, ‘Speech
Interpretation in Auditoriums”’, which
appeared in the RecorpD for October,
has been reprinted in the December
issue of the Gamma Alpha Record.

H. EckuaArpT made phonograph
records at Houlton, Maine, of trans-
atlantic conversations between Austin
Bailey of the Long Lines Department
at 24 Walker Street, and Colonel
Shreeve, at London, on January 7 and
8. Simultaneously, E. Peterson re-
corded these conversations at the La-
boratories.

C. S. GorDoN visited the New
York Insulated Wire Company at
Wallingford, Connecticut, on Decem-
ber 6 in connection with the prepara-
tion of trial lots of drop wire.

E. M. Honan was in Boston to
discuss with members of the Simplex
Wire and Cable Company problems
dealing with the manufacture of rub-
ber-insulated wire.

C. D. Hocker ann F. F. FARNs-
WORTH visited several of the asso-
ciated telephone companies in the
middle west, as well as the plants of
several automobile body manufactur-
ers and paint companies, to investi-
gate paint finishes for automotive
equipment.

C. Q. LUMSDEN was engaged in stu-
dies of chestnut poles at Shipman,
Natural Bridge and Waynesboro,
Virginia, from December 20 to 22.

M. B. Lone addressed the Phila-
delphia Section of the A. I. E. E. on
January 14, on the subject of the pho-
toelectric cell and its use in com-
munication. Prior to the meeting,
Mr. Long was the guest of the En-
gineers Club at dinner.

Eyes and Their Use in Communica.
tion” before the Engineers Club of
St. Louis on January 9, the South.
western Bell ‘Telephone Company em.
ployees on January 10, and on Janu-
ary 11, he addressed the engineering
students of Washington University,
The following day, Mr. Mills spoke
on the same subject before the Round
Table of the University.

S. P. GRACE addressed the staff of
the Carson Peck Memorial Hospital
in Brooklyn on January 10, on recent
developments of the Laboratories,
Mr. Grace also lectured before the
Engineers Club of Cincinnati.

T. W. CLarkeE has been elected to
membership in the Edward J. Hall
Chapter of the Telephone Pioneers.

HELEN O. LUEDTKE, a stenog-
rapher in the Transcription Depart-
ment, died on Friday, January 4. Miss
Luedtke had been a member of the
Laboratories since February, 1926.

H. M. ANDERSON, a shop mechanic
in the Plant and Shops Department,
died on December 14. Mr. Anderson
had been associated with the Labo-
ratories since March 6, 1918.

MEMBERS OF THE PATENT Dr-
PARTMENT who went to Washington
during the period from December 11
to January 10, in connection with the
prosecution of patents were: E. W.
Adams, W. C. Kiesel, I. MacDonald,
T. P. Neville, J. W. Schmeid and G.
H. Stevenson.

F. F. Lucas spoke on metallog-
raphy before the American Society
for Steel Treating at Buffalo.

S. J. ZAMMATARO’S article, “‘Devel-
opment of the Impedance Bridge,”
which appeared in the Recorp for
December, has been reprinted in full

J. R. TowNnsenp’s article, “New
Specifications for Raw Materials,”
which appeared in the Recorp for
February, 1928, has been reprinted in
the December issue of “‘Instruments.”

O. L. WALTER discussed suggested
changes in the 202-B reproducer set
at Hawthorne.

J. C. Herser’s article, “Frequency
Control for Broadcasting”, which ap-
peared in the ReEcorD for September,
has been reprinted in the November
issue of the Bent of Tau Beta Pi.

S. J. ZAMMATARO AND T. SLONC-
ZEWSKI visited the Leeds and North-
rup Company at Philadelphia to in-
spect shielded-type precision bridges.

H. BROADWELL attended confer-
ences at Hawthorne on the manufac-
ture of precision interrupters.

F. H. visited Chat-
tanooga, Tennessee, and Atlanta,
Georgia, in connection with the revi-
sion of adjustment requirements on
step-by-step relays.

W. L. HEArpD, as a member of the
Standards Committee of the A. I. E.
E., has participated in the prepara-
tion of graphical symbols for tele-
phone and telegraph use. This work
has now been completed, the symbols
and abbreviations have been approv-
ed as an Institute standard and they
are being transmitted to the Ameri-
can Standards Association.

E. H. SmirH spent a week at Chi-
cago discussing step-by-step central-
office equipment.

J. R. STONE AND H. L. MUELLER
discussed exhaust equipment for pneu-
matic tube systems and various power

machine problems with representa-
tives of the General Electric factory
in West Lynn, Massachusetts.

W. O. FULLERTON inspected at
Rochester the new 506-A cordless
P. B. X. being built by Stromberg-
Carlson.

V. T. CALLAHAN discussed gas en-
gine mufflers with members of the
Maxim Silencer Company at Hart-
ford, Connecticut.

E. J. KANE ann J. M. Ducutn in-
vestigated busy-tone wiring in the
step-by-step office at Hartford.

G. E. Battey R. E. NosBie
recently inspected a new type of super-
structure for frames and racks in-
stalled at Laurel Springs, New Jersey.

L. P. BARTHELD discussed cabling
problems in the new Chicago Toll
Office with Illinois Bell engineers.

C. ECKBERG is arranging for in-
stallation of improved radio broad-
casting circuits at various repeater
stations on the Pittsburgh-New York
cable.

C. BORGMANN visited Boston, Chi-
cago and Rochester in connection with
equipment problems.

W. J. LAcerTE visited Hartford
and Atlantic City in connection with
improved circuit arrangements for
step-by-step central offices.

On page 186, last paragraph, the
number of regulators in the Long
Lines plant should have been given
as 41.

In the second paragraph on page
189 the second sentence should read
“Under these conditions on a full
size cable there is an IR drop along

During the month of March the
Club will hold an indoor handball
tournament at Labor Temple, Four-
teenth Street and Second Avenue,
Manhattan. Play will commence
Tuesday evening, March 5, and
matches will be held on Tuesday and

Thursday evenings from 5:30 to
7:30, for four weeks. ‘The single-
wall form of play will be used, and
all games will be singles. The tourna-
ment will be conducted on an elimina-
tion basis, with all matches up to the
semi-finals consisting of a single game.
Semi-finals and finals will be decided
by two games out of three. The win-
ner will receive an order good for ten
dollars’ worth of merchandise at Alex.
Taylor and Company, the second
man, an order worth five dollars, and
the two men eliminated in the semi-
finals will each get an order worth
two dollars and a half.

Entry blanks may be obtained from
D. D. Haggerty, Room 164, and must
be returned to him with the entry fee
of twenty-five cents not later than
Monday, February 25. Before each
round, players will be advised of date,
time and opponents with whom they
have been matched.

Plans have been completed for the
final tournament of the indoor golf
season, which will be played on Wed-
nesday evening, February 27, at the
Miniature Golf Course of America,
41 East 42nd Street, Manhattan.

As in previous tournaments all con-
testants will play thirty-six holes of
medal play in the qualifying round
after which they will be divided into
two groups of four flights each with
prizes for the winner in each of the
eight flights. Sixty-four players will
be qualified for the finals.

Entries should be forwarded to D.
D. Haggerty, and accompanied by an
entrance fee of $1.50.

by the Club, a valuable prize will be
donated by the management of the
golf course.

The annual Photographic Contest,
open to all the members of the La-
boratories, is now under way. Entries

should reach D. D. Haggerty before
March 1, after which date they will
be exhibited and judged. Prints are
to be divided into four classes: por-
traits, landscapes, still life and col-
ored transparency. For further in-
formation regarding rules and prizes,
call Margaret Horne, Extension 786,
or D. D. Haggerty, Extension 542.

It is the wish of the music commit-
tee that every department of the La-
boratories be represented in the Glee
Club. The active membership may
be divided as follows: Systems De-
velopment, 12; Patent, 11; Appara-
tus Development, 6; Research, 5; Ac-
counting, 2; Inspection, 1.

Trained voices are not necessary,
but a fairly good voice and some abil-
ity to read music are desirable. The
Glee Club is now rehearsing for a
formal recital to be held in April as
a part of the Spring Dance and Enter-
tainment of the Club. For that rea-
son, new members will not be ac-
cepted after March 1. Meetings are
held every Wednesday evening from
5:10 P. M. to 6:10 P. M. in the
Women’s Rest Room on the eleventh
floor. For further information call

The men’s bridge club recently
completed its ten-week tournament
and on Monday, January 7, and Mon-
day, January 14, sixty men took part
in an elimination tournament to de-
termine who would represent the
Club in the annual tournament with
the Western Electric Bridge Club.
This match will be held on Monday
evening, March 4, at 195 Broadway,
and forty players from each company
will compete for the trophy, now held

A second tournament of ten weeks’
duration was started by the members
of the Club on Monday evening,

January 28. This group meets each
Monday evening in Rooms 275 and
277 and the committee in charge is
always glad to welcome new players.

The women’s bridge club played
the first game of the mid-winter tour-
nament on Friday, January 5th. The
tournament will continue for ten
weeks and in order to be eligible for
tournament prizes players must take
part in at least seven out of the ten
games.

The bridge club conducts a meeting
every week, at which prizes are given
for high scores. Those interested
may apply to Mary V. Lynch.

Until further notice the orchestra,
which formerly met on Thursday
evenings, will meet on Tuesdays at
5:05 in the Women’s Rest Room. A
buffet supper will be served by the
restaurant management in the Rest
Room at 5:45.

The orchestra, for a time under
the leadership of Mr. Egon Elbert,
a professional conductor, is again be-
ing conducted by L. E. Melhuish.
Mr. Melhuish stresses the fact that,
although regular attendance at re-
hearsals is desirable, the program for
the remainder of the season has been
so arranged as to make it interesting
for those who cannot attend each of

A class of music suitable to the
number attending rehearsals will be
undertaken. Members are encouraged
to suggest selections for rehearsals,
which the club in turn will be glad to
procure. The repertoire now consists
of standard overtures, operatic selec-
tions, symphonies and popular selec-
tions from musical comedies.

season begins with a reorganization
of the women’s bowling group under
the supervision of a committee of men,
appointed by the General Chairman
of the men’s bowling league. This
committee is looking after the inter-
ests of the women bowlers, with a

view to promoting an enthusiastic and
successful season.
Arrangements may be made

through Antoinette Kelly or Marian
Kane to have one’s name placed on
the substitute list.

With the close of the bowling sea-
son, a dinner and theatre party will
be given to the bowlers. At dinner,
prizes will be awarded to the winners.

Bell Laboratories Record 1929-02: Vol 7 Iss 6