single pair of conductors by using
frequencies above the voice range.
The greater the frequency range the
more telephone channels can be oper-
ated on the same conductors. Carrier
transmission is therefore attractive,
but there are, of course, serious tech-
nical barriers, due to the tendency, in
general, for the circuit losses and in-
terference effects to increase as the
frequency is raised, and to problems
incident to the stepping up and down,
and to separating the high frequencies.
By 1918, these problems had been
solved to a degree sufficient to enable
the first multi-channel carrier-tele-
phone system to be designed and put
into commercial service. A_ later
standardized system—the Type-C—
which by using frequencies up to
30,000 cycles, provides three tele-
phone circuits in addition to the regu-
lar voice circuit on a single pair of
open wires, has been extensively ap-
plied all over the country.

In the meantime, development en-
gineers have been working to widen
the frequency range to obtain more
circuits on a single pair of conductors,
and to extend the usefulness of the
method by applying it to the fine-wire
pairs in cables as well as to open-wire
lines. They have also been developing
a new type of transmitting structure,
especially suitable- for transmitting
very high frequencies, this being
known as the coaxial circuit.*
~ *Record, July, 1935, 322.

From this work three new carrier
systems are resulting. Because of the
wide band of frequencies they trans-
mit, these are all classed as broad-band
systems. One system, for cables, whose
development is fairly well completed,
will give 12 telephone channels on
each pair, using frequencies up to
60,000 cycles. Another, the coaxial
system, in its experimental form, could
be used to give 240 circuits, using a
frequency range up to one million
cycles. The third system under de-
velopment is for open-wire lines, and
will provide 12 telephone circuits in
addition to the three circuits of the
existing T'ype-C system and the voice
circuit, 16 circuits in all on a single
pair of conductors. The top frequency
is 140,000 cycles.

On the open-wire lines the large
gauge and wide spacing of the con-
ductors are favorable to high-fre-
quency transmission, but this exposed
type of structure is difficult to keep
free from unwanted currents induced
by other nearby telephone circuits, by
power lines, lightning, or other outside
disturbances. The limiting factor in
using higher frequencies on open-wire

lines has generally been induction or
crosstalk between nearby circuits.

Until recently 30,000 cycles, the top
frequency of the Type-C system, repre-
sented about the upper limit of trans-
mission from the standpoint of keep-
ing similar systems on different pairs
from crosstalking unduly one into an-
other. Crosstalk on open-wire lines is
reduced by applying transposition
systems; that is, the wires of a pair are
crossed over at predetermined inter-
vals so that the induc-
ing potentials and cur-
rents tend to balance
out. For high frequen-
cies these transposi-
tions have to be made
very frequently and
precisely. There have
been certain important
developments in the
art of transposition de-
signing during the last
few years; also the
spacing between the
two wires of a pair is
being reduced from 12
inches down to 6 or 8
inches so that there is
a greater distance be-
tween the pairs and
less direct pickup by
each pair. These im-
provements will make
it possible to raise the
frequency to about 140
kilocycles, thus paving
the way for the 12-
channel carrier systems
which are being de-
signed.

The fine-gauge pa-
per-insulated pairs in
existing cables do not
inherently make good
high-frequency con-
ductors; the attenua-

tion is too great. This is offset to some
extent by the shielding effect of the lead
sheath, which largely excludes external
disturbances, and thus permits greater
amplification at repeater points than
can be used with open-wire circuits.
Even so, repeaters will be required at
much more frequent intervals than for
the open-wire line for a corresponding
frequency of transmission. Here again,
crosstalk between the pairs, which in
cables are packed close together, is

the practical limiting factor in deter-
mining the upper frequency and the
number of channels which can be ap-
plied. Since the pairs in a cable are
twisted, or in a sense transposed with
respect to each other, in such a way
that they can not be changed after
having once been installed, there is
no way of improving the crosstalk
situation comparable to changing the
transposition system as with open-
wire lines.

It has been discovered recently,
however, that it is possible to balance
out, to a large extent, the crosstalk
between the different pairs on which
carrier systems are to be applied, by
using small adjustable inductances or
condensers. These balancing units will
be connected at intervals between all
the pairs involved. A separate balanc-
ing unit is required between a given
pair and each of the other pairs in-
volved. In this way the practical fre-
quency range of operation on the cable
pairs is being extended from a few
thousand cycles to about 60,000 cycles.

In the coaxial conductor, the engi-
neers set out to design a new structure
which would combine the favorable
low attenuation characteristic of the
open-wire lines with the interference-
free characteristic of shielded cable
circuits. With such a structure a large
number of circuits can be obtained on
but one set of conductors, using a
frequency range up to a million cycles
or more if necessary.

In a coaxial unit, the outside tube is
a good metallic shield at the high fre-
quencies. If currents are induced from
external fields, such as power circuits,
static, or lightning, they tend, because
of skin effect, to confine themselves to
the outside surface of the tube, while
the useful currents for the same reason
are on the inside of the tube. The
space between the inside conductor

and the outside tube is largely air,
which is a good dielectric having no
losses. The spacing insulators of hard
rubber fill up only a relatively small
proportion of the space, and they are
of low-loss material. Also, the tube
conductor is particularly well propor-
tioned to offset skin effect and thus
reduce the series losses. It should be
noted, however, that a very satis-
factory high-frequency conductor can
be made of a pair of wires separated
by spacers within a metallic shield.
Such balanced pair structures may
also play a part in future high fre-
quency transmission systems.

While these various broad-band
systems have different frequency
ranges, they have many common
fundamental problems. Probably the
most important is that of the re-
peater or amplifier. In all cases the
repeaters are spaced much more fre-
quently than is necessary for lower
frequencies. The approximate inter-
vals are: for the cable system, 16
miles; for the million-cycle coaxial
system, 10 miles; for the open-wire
system, 50 to 100 miles. This means
using many amplifiers in tandem,
which in turn means that each ampli-
fier must be quite perfect. Elaborate
regulating means must also be pro-
vided to make the amplifiers compen-
sate for the varying attenuation of the
line circuits with temperature or
weather changes. The regenerative or
negative-feedback type of amplifier,
which has already been described in
these pages,* is employed in the dif-
ferent broad-band systems. It has a
tremendous advantage over older
types from the standpoint of stability,
freedom from battery variations, and
in linearity or perfection of amplifi-
cation. The improvement over other
amplifiers in these respects is a hun-
~ *REcorD, June, 1934, P. 290.

dredfold or more, and thus puts the
feedback amplifier in a class by itself
for purposes of this kind.

Amplifiers require power, and the
power plant designers have been busy
producing new types of battery re-
serve plants for the auxiliary repeater
stations which will be added between
existing stations. For the coaxial sys-
tem, means have been provided for
transmitting the power for the re-
peaters over the structure itself.

The highest repeater amplifications,
some 60 or 70 db, will be employed
with the well-shielded conductors,
that is, the cable pairs and coaxial
systems. This is about 20 db, or about
a hundredfold power ratio greater
than amplifiers employed in the tele-
phone plant in the past. It is interest-
ing to note that here, for the first time,
repeaters will be employed in which
the degree of amplification is set, not
by external interference, but by inter-
ference which arises within the con-
ductors themselves — the so-called
thermal noise or resistance noise*.
The motion of the free electrons within
the conductors sets up tiny electro-
motive forces which have a spread-out
frequency distribution covering the
entire frequency spectrum. This in
effect is Nature’s own limitation to
the amount of amplification which can
be employed in any system.

It should not be judged, however,
that other interference problems are
absent in the case of the sheathed
conductors. For example, in the case
of the cable-carrier system, there has
been a particularly severe problem in
reducing the man-made interference,
which arises within telephone offices
when battery circuits are broken by
the operations of switches and relays.
Each current break creates a tiny
high-frequency oscillation, the effects
~ *REcorD, February, 1937, p. 185.

of which are readily picked up by in-
duction in the various cable pairs as
they pass through the building. In
applying the cable-carrier system, it is
necessary, therefore, not only to shield
the carrier pairs and apparatus in such
offices but to keep this artificially
created interfering current from trav-
eling out along the other wires in the
cable and crosstalking into the pairs
used for carrier systems. High fre-
quency filtering circuits will therefore
be applied to all the non-carrier pairs
where a cable leaves such an office.

A common part of all of the broad-
band systems is a group of modulating
and filtering equipment that provides
twelve voice channels over the fre-
quency range from 60 to 108 kilocycles.
In the system for cable circuits one of
these groups is transmitted over a
single pair of wires, but by a second
step of modulation it is placed in the
frequency band from 12 to 60 kilo-
cycles. A similar group of channels on
another cable pair is used for the re-
turn transmission.

The open-wire systems will use two
of the 12-channel groups on each pair,
one for each direction of transmission,
the first placed by a step of modula-
tion above 30 kilocycles, which is the
upper limit of the present three-
channel system, and the second, for
return transmission, above it, with a
top frequency of about 140 kilocycles.

The coaxial system, as at present
being used experimentally, can trans-
mit 20 groups in the frequency range
from 60 to 1020 kilocycles, employing
a second modulation for 19 of the
groups. This, as noted, gives 240
channels. A similar coaxial provides
the 240 opposite directional channels.
Ultimately such systems will probably
be arranged to transmit a _ con-
siderably greater number of channels.

the coaxial and cable-carrier system it
is found better to use different me-
tallic circuits for opposite directional
transmission than to use different fre-
quencies on the same pair as has been
a common practice on open-wire lines.
One reason is that in these systems,
repeaters will be needed so often, that
the directional filters which would be
necessary at each repeater point to
separate the opposite directions of
transmission would unduly increase
the costs. In the open-wire systems,
the attenuation is lower, as noted
previously, repeaters will be 50 to 100
miles apart; and it is feasible to use
directional filters. Furthermore, on
open-wire lines there are no possibili-
ties of getting the necessary high de-
gree of opposite directional crosstalk
separation except by using different
frequencies. Separate pole lines are
obviously impractical.

To summarize—broad-band sys-
tems will use much greater frequency
ranges than has been practicable in
the past. For the most part these
broad-frequency ranges will be
chopped up into narrow bands for
telephone or telegraph purposes.
Bands of several million cycles in co-
axial conductors can if needed also be
made available for television pur-
poses. Each of the new systems will

fill a useful place in the Bell System
plant—the cable and open-wire sys.
tems, particularly where these lines
already exist—the coaxial system
where new structures are needed,
and, in particular, on the heavy traffic
routes. Of course, considerable com-
plicated equipment is required and
for the immediate future these various
systems will probably be found eco-
nomical chiefly for transmission over
the longer distances.

One not obvious but important ad-
vantage deserves mention in closing.
Broad-band systems are all being ap-
plied on non-loaded conductors. This
means that they are high-speed sys-
tems whose wave velocity approaches
that of light. As a matter of contrast,
the older type, long-haul, four-wire
loaded cable circuits have a velocity
of only 20,000 miles per second as
compared with 100,000 miles and up-
wards for the broad-band systems.
On 20,000-mile-per-second circuits,
problems of echoes are exaggerated
and even two-way talking may be
awkward on circuits several thousand
miles long, because of the time taken
for a talker at one end of a circuit to
be heard at the other end, and to re-
ceive a reply. Broad-band high-speed
circuits will practically relieve us of
concern about matters of this kind.

PPARATUS for measuring at-
tenuation loss at high frequen-
cies has received considerable

attention by the Laboratories during
the past few years. This has been found
necessary because of new require-
ments imposed by broad-band carrier
telephone systems. These systems in-
clude a large number of filters and
equalizers, the design and production
of which depend in part on having
available accurate means of measur-
ing their loss-frequency characteris-
tics. The measurements are made by
applying an electromotive force of
known frequency to the equipment
under test and to a standard attenu-
ator and adjusting the attenuator
until the loss is the same in both cir-

cuits. The attenuation of the equip-
ment under test can then be read di-
rectly on the standard attenuator.

A fundamental circuit of the type
used is shown in Figure 1. The output
of an oscillator, which can be varied
continuously in frequency from 50 to
5000 kc, is applied simultaneously to
the input of the apparatus under test
and the standard attenuator through
terminating resistances. The appa-
ratus and attenuator terminate at the
other ends in resistances which are
equal to the characteristic impedances
of the apparatus and attenuator re-
spectively. The detector is a’ super-
heterodyne and a microammeter indi-
cates the point of balance because the
ear cannot detect small enough dif-

ferences in sound level to make head
phones satisfactory for precision work.

The errors due to the inherent i1n-
ductance and capacitance of the cir-
cuit increase with frequency. If the
circuit impedance is made high, the
error due to the shunt capacitance be-
comes predominant, and conversely if
low the error due to the series induc-
tance predominates. For the frequency
rangeofthiscircuit, animpedanceof 100
ohms was chosen as the best compro-
mise. These limitations also prohibit
the use of decade resistances for termi-
nations and small plug-in resistors
were, therefore, developed for the pur-
pose. These resistors have a smaller
phase angle than the decade type and
allow the set to be kept more compact.

Losses of at least 80 db have to be
measured to determine the attenua-
tion peaks of filters. In making bal-
anced-to-ground measurements of
losses of this magnitude, longitudinal
currents, which flow down both sides
of the circuit and return through
ground or by some other path, are the
principal cause of error. Since these
currents are not in general the same
in either phase or magnitude in the
two branches of the circuit, they re-

sult in a false balance if they flow into
the detector. To reduce this error, the
circuit is isolated at input and output
with carefully shielded and balanced
repeating coils. A grounded center tap
on the measuring set side of the out-
put coil gives a low impedance path to
ground for the longitudinal currents.
In addition to this it was found neces-
sary to use wire having a very tightly
woven copper-braid shield for all leads
between the component parts of the
set-up and to make sure that these
wire shields are continuous with the
external shields of the apparatus.
This was done in the latest set con-
structed by using recently developed
coaxial plugs and jacks for making all
connections between the necessary
leads and the apparatus.

In attempting to make high loss un-
balanced measurements it was found
necessary to construct the input and
output sections of the measuring set in
separate shielded compartments which
were insulated from each other. This
was required to eliminate multiple
ground paths.

The absolute accuracy of the meas-
urements made with a circuit of this
kind is dependent upon the accuracy

Fig. 1—Attenuation at radio frequencies is measured by comparing the loss in the
apparatus under test with that of a standard attenuator

Standard attenuator constructed with parallel-opposed resistance units wound

of the attenuator used as a standard.
It has, therefore, been necessary to
develop attenuators having negligible
frequency errors along with suitable
measuring circuits. These attenu-
ators are made of constant-impedance
resistance networks provided with
suitable means for switching. Any re-
actance in these resistances or in the
associated switches and wiring results
in increasing departure from the theo-
retical value of the attenuator as the
frequency is increased. This undesir-
able effect has been reduced by taking
advantage of recent improvements in
winding low-phase-angle resistances.
Two types are being used at present;
one with a parallel-opposed winding
on a small glass tube and the other,
which may be wound to higher resist-
ance values, of the woven wire type.
In both forms the phase angle is
negligible except for very low or very
high resistance values.

Two types of both balanced and un-
balanced attenuators which use these
resistors have been developed. In one
type, shown in Figures 2 and 3, the
networks are cut in or out by means of
double-pole double-throw keys. These
are relatively inexpensive but have
the disadvantage that the reactance
of the keys and wiring of the networks
not in use is still in the circuit. Rotary
switches are used in the other type
which represents a distinct improve-
ment over previous switching methods.

An unbalanced attenuator of this
type is shown in Figure 4. As may be
seen the networks are connected di-
rectly between the switch contacts;
this allows the wiring to be kept at a
minimum. The construction of the
switch is such that the spurious ca-
pacitances are extremely small; other-
wise they would be very troublesome
at the higher frequencies. The switch
which has 10 db steps is double decked

Fig. 3—The resistances of this standard attenuator are mounted in two rows with keys
between to cut the units in and out

with a network in each deck for losses
above 30 db. Splitting the higher
losses into two networks in this man-
ner keeps the series resistances from
becoming unduly high and also helps
to decrease the direct capacitance be-
tween input and output. A shield
plate is inserted between the two
decks and the complete switch is en-
closed in a shielding box.

To reduce still further the direct ca-
pacitance between input and output
of the switch it was
necessary to include
additional brushes to
ground the adjacent
network on either side
of the one in use. Much
thought and _ experi-
mentation was re-
quired to work out the
proper method of mak-
ing the various ground
connections on this at-
tenuator, since the
ground impedance
must be properly
placed in the circuit if
accuracy is to be ob-

tenuators of this type it is now pos-
sible to measure losses of go db at 5000
ke with an accuracy of 1 db. This is a
considerable improvement over equip-
ment previously available.

The oscillator must be extremely
well shielded and must have high
stability in amplitude and frequency
if precision measurements are to be
obtained. The detector must likewise
be well shielded and must have high
sensitivity and also stability. A tuned

tained at the higher Fig. 4—Standard attenuator of the unbalanced type with

Fig. s—The input and output sections of the measuring set are in separate shielded
compartments with space for the apparatus under test and the standard attenuator

detector is necessary to prevent errors
due to oscillator harmonics for meas-
urements in the attenuating range of
networks. A superheterodyne type of
detector seems to meet all of the re-
quirements in the simplest manner.
The intermediate frequency is modu-
lated by a built-in oscillator so that a
frequency of approximately 1000
cycles is obtained in the output. In
the latest form the indicator consists
of a diode-triode rectifier tube with a
microammeter connected in the plate
circuit of the triode section. By proper
choice of circuit constants a 3 db
linear scale can be obtained on this
meter which makes it possible to read
a balance with a precision of 0.05 db.
This meter can be calibrated at 1000
cycles and then serves as a check on
the accuracy of the attenuator in the
high-frequency circuit for small in-
creases in attenuation. The use of a
calibrated meter makes steps smaller
than one or two db unnecessary on the
attenuator and thus saves the expense
of several additional keys. or one
decade. A further advantage is that

the tube cuts off on overload so that it
is impossible to damage the meter.

An attenuation measuring set em-
bodying the latest developments is
shown in Figure 5. The repeating coils
are provided with plugs and are in-
serted in different jacks for balanced
and unbalanced measurements. Two
sets of coils are provided, one covering
a nominal frequency range of 50 to
1500 ke and the other from 1500 to
10,000 ke. By the lower key the out-
put coil is switched from the attenu-
ator to the apparatus under test; the
upper key gives a 180-degree phase
shift in the input to the detector and
thus serves as a check on the presence
of longitudinal currents when meas-
uring balanced apparatus. The equip-
ment to be measured is connected be-
tween the jacks in the lower corners
and those above either to a balanced
attenuator or an unbalanced one.

The increased accuracy attainable
with the new equipment will make it
useful in development work where
precise measurements of insertion loss
at high frequencies are required.

taining and improving the ser-
vice have required some method of
measuring noise on telephone circuits.
At first a simple form of listening test
was used, and the amount of noise
tolerated depended largely on the
judgment of those operating the tele-
phone plant. This led to different
standards in different localities, which
naturally was not a satisfactory ar-
rangement, and as a result the method
was supplanted by the use of the 1A
noise measuring set. This set in-
corporates a buzzer to produce a noise,
and a potentiometer with which the
noise volume may be varied over a
wide range. By listening alternately
to the noise on the circuit and to the
output of the measuring set as the
latter is reduced in volume by the po-
tentiometer, it is possible to find the
point at which the two may be judged
to produce the same interfering effect,
and the reading of the potentiometer

Fig. 1—The 2A noise measuring set, with cover removed,
showing arrangement of apparatus on the front panel

Although the 1A noise measuring set
was a great improvement over pre-
viously existing devices, the results
obtained with it did not attain the
degree of objectivity desirable, since
they rested in the ultimate analysis
on a personal subjective judgment.
This judgment required the balancing
of an adjustable amount of standard
buzzer noise against the unknown
amount of circuit noise, not on the
basis of equal loudness but on the
basis of the interfering effect of the
noises on the interpretation of speech.
If the buzzer and circuit noises differed
greatly in quality the balance was
difficult. Unless care and good judg-
ment were exercised, two noises that
were judged to be equivalent by use of
the 1A set might be found to have
different interfering effects on a trans-
mitted conversation.

The defects of the 1A set were
largely remedied in the 1A Noise
Amplifier, brought out
in 1929 for measuring
noise in toll offices. This
amplifier employed fre-
quency weighting based
on the then available
data on the relative in-
terfering effects of
single-frequency tones,
and used the 6A Trans-
mission Measuring Set
as an indicating device.
By eliminating the ear
as the basis for deter-

mining the noise magnitude, a distinct
gain in objectivity of measurement
was made, but the set fell short of the
ideal in other ways, such as porta-
bility, dynamic characteristics of the
indicating instruments, and additional
frequency weightings.

Recently a new noise measuring set
has been brought out that goes much
farther toward realizing the primary
objectives of noise measurements. This
set, shown in Figure 1, is known as the
2A noise measuring set, and incor-
porates the results of many years’ re-
search on the problem of noise meas-
urement. It carries its own power
supply in the form of dry cells, and is
designed to be used as a portable
instrument although brackets may be
obtained for mounting it on central
office frames when desired.

The interfering effect of noise de-
pends, in general, on its frequency
composition, on the relative magni-
tude and spacing of the various fre-
quencies, on the duration of the noise,
on the type of circuit on which it
occurs, and on the person who is listen-
ing to it. This large number and
variety of factors very greatly compli-
cates the design of a satisfactory noise
measuring set. The subjective element
of noise is largely eliminated by em-
ploying a meter to give the indication
of noise; but before such a method can
be satisfactorily used, much research
must be done to determine the inter-
fering effects of different noises on
speech as heard by the ear, and then
circuits must be incorporated in the
set between the noise input and the
meter to simulate the action of the ear.

Since the effect of noise depends to a
very large extent on its component fre-
quencies, a weighting network is in-
corporated in the set to attenuate the
noise frequencies in inverse ratio to
their interfering effect. The impor-

tance of various frequencies depends,
however, on the type of circuit and on
the position in the circuit where the
noise is being measured. On an ordinary
telephone circuit, for example, which
does not efficiently transmit fre-
quencies above about 3000 cycles, a
noise frequency of 5000 cycles would

Fig. 2—Circuit arrangement of noise set
when connected through “‘line” jacks, “re-
ceiver” jacks, and ““program’”’ jacks

If the noise were of a single fre-
quency, these networks would insure
that its measured effect would be that
determined by the average ear for

representative amplitudes of both
speech and noise; but when, as is
usually the case, the noise comprises
many frequencies, the action of the
ear in combining different frequencies
must also be considered. The measur-
ing set includes a rectifier for convert-
ing the alternating noise current to a
direct current for actuating the meter,
and this rectifier is designed to com-
bine the weighted noise currents in
such a way that the sum is approxi-
mately equal to the square root of
the sum of the squares of the weighted
components. Tests have been made
which show that this rule of combina-
tion is similar to that in the ear for a
number of common noises.

After all these adjustments of the
noise have been made, the period of
duration of the noise must still be con-
sidered. As a result of considerable
research, it has been found that for
the usual noises found on telephone
circuits a time of about 0.2 second is
required for the noise to be fully ap-
preciated by the ear. To incorporate
this factor into the measuring set, the
indicating meter has been given such
dynamic characteristics that a noise

enduring for 0.2 second will produce
the same deflection that a continuous
noise would, while noises of shorter
duration produce proportionally
smaller deflections. For intermittent
noise, such as static, this dynamic
characteristic makes the meter some-
what more difficult to read, but by
establishing rules for reading the meter
on intermittent noises, approximately
equal meter readings can be obtained
for both steady and intermittent noises

having equal interfering effects.
Besides these elements already dis-
cussed, the noise set must also include
a coupling or connecting circuit so as
to present a suitable impedance to the
circuit to which it is to be connected.
The complete measuring set thus in-
cludes an input circuit, a weighting
network, an attenuator, an amplifier,
a rectifier, and an indicating meter.
The last four elements will remain the
same regardless of the type of circuit
or the point of measurement, but pro-
vision must be made for suiting the
weighting and input networks to the
particular measurement being made.
This is accomplished by incorporating
in the set the various networks re-
quired, and by provid-

transmission between the line and the receiver, which is the
difference between curves A and C

2500 various types of meas-
urement. Connection
from the line under test
is usually made to a
pair of binding posts,
and a plug—connected
to these binding posts

Fig. 4—Weighting curve for program circuits, curve
A, and for sound and volume measurements, curve B

The bottom pair of jacks is marked
“line,” and is used for measuring
noise on a telephone circuit at some
other place than the subscriber’s re-
ceiver—for example, at the toll office.
Its input circuit presents an impedance
of 600 ohms so as to match the line
impedance. The circuit arrangement
is shown at the top of Figure 2. The
weighting network used for this con-
nection has the characteristics shown
by curve A of Figure 3. This curve
represents the sum of two weightings,
viz., a frequency weighting for the
relative interfering effects of single
frequency voltages in the telephone
receiver (curve C) and the frequency
characteristic of the circuit between
the line and receiver (curve B).

When measurement is to be made
at the subscriber receiver, the set is
connected across the receiver and has
a high input impedance. The circuit
employed, shown in the center of
Figure 2, has an impedance of about
2000 ohms. A different weighting net-
work is required for measurements at
the subscriber’s receiver because of
the frequency characteristic of the
attenuation between the line and
receiver terminals of the telephone
set, which is indicated by curve B of
Figure 3. The weighting characteristic
provided is therefore that shown by

shown in the lower part of
Figure 2, but a different weight-
ing characteristic is required
because of the wider trans-
mitted band of frequencies. The char-
acteristic employed is shown as curve
A on Figure 4.

While these three types of measure-
ments are those that will be most
commonly employed, the usefulness of

Fig. s—Circuit arrangements for measure-
ments of noise to ground, above; of sound, in
center; and of volume, below

the set has been widened by providing
jacks for four other types that prove
advantageous under various condi-
tions. It is sometimes desirable, for
example, to measure noise on a tele-
phone circuit without breaking the
circuit. To make this possible a
“bridging” input circuit is provided,
which presents an impedance of about

6000 ohms. The output of this circuit
is connected to the input of the “‘line”’
circuit, and it thus uses the same
weighting network.

In making any of these measure-
ments the potentiometer is turned
until the meter pointer is on the scale,
and the noise magnitude is then the
sum of the readings of the potentiom-
eter and the meter—the potentiom-
eter having a range of 60 db, and the
meter, of 18 db. Reference noise in all
cases is the meter reading that would
be obtained with 10-!? watts of 1000-
cycle power dissipated at the point of
measurement.

Another input circuit, shown at the
top of Figure 5, makes it possible to
measure noise voltage to ground. This
measurement is often desirable when
it is expected that large longitudinal
voltages are operating through circuit
unbalances to cause metallic-circuit
noise. This circuit consists of a 100,000-
ohm input circuit and the “line” input
circuit in series. Reference noise to

A “sound” input circuit, shown
schematically in the middle of Figure
5, permits the set to be used, with the
aid of a microphone and matching
transformer, for measuring sound
levels. Minimum measurable level
depends on the sensitivity of the mi-
crophone and the efficiency of the
transformer, but with the 630A micro-
phone and the 115A repeating coil,
sound levels as low as about 55 db
above reference sound level can be

measured. The weighting employed is
that shown by curve B of Figure 4.
Reference sound level corresponds to
10-!6 watts per square centimeter at
1000 cycles in a free progressive sound
wave in the open air.

By use of the “volume” input,
shown schematically in the lower part
of Figure 5, volume measurements
may be made on message circuits, but
not on program circuits, because the
response of the volume circuit is not
flat, the weighting being the same as
for the “sound” circuit. The rela-
tively low response in the volume
circuit at low frequencies is not of
great Importance in measuring message
circuit volumes, but causes serious
errors in measuring volumes on pro-
gram circuits.

The upper pair of jacks and the
telephone set dial are used for cali-
brating the set. Operation of the dial
sets up a train of waves which impress
a predetermined input across the set.
The gain of the amplifier is then ad-
justed until the peak swings of the
meter pointer (ignoring the first deflec-
tion) are on a red line marked on the
scale. This method gives a calibration
for all circuits by a single operation.

Although the 2A Noise Measuring
Set is not a perfect instrument for all
conditions, the results of a wide range
of tests indicate that it agrees better
with tests of the effects of noise than
does any other apparatus available.
Its applicability to a wide variety of
conditions should make it very useful
in maintaining satisfactory noise con-
ditions in the telephone plant.

F. B. Llewellyn spoke on The Inside
Story of the Vacuum Tube at the February
15 meeting of the Colloquium. According
to Dr. Llewellyn there has been recently
a renewed interest in finding out what
happens to electrons on the inside of
vacuum tubes. Although this was brought
about largely by the requirements of
ultra-high-frequency operation, the re-
sults have thrown additional light on the
performance of tubes at much lower fre-
quencies. Several funda-
mental properties of elec-
tron streams were dis-
cussed, and their influ-
ence on tube operation
described in terms of
equivalent circuits.

At the meeting held on
March 1, G. K. Teal dis-
cussed The Application of
Raman Spectra to Physi-
cal and Chemical Prob-
lems. In 1928, C. V.
Raman found that the
light scattered by an or-
ganic liquid illumined
with visible radiation of
a single frequency con-
tained not only the origi-
nal frequency but also
certain other frequencies
characteristic of the liq-
' uid being studied. It soon
became evident that the
Raman Effect was a new
phenomenon giving in-
formation concerning the
rotation and vibrations
of molecules and that it
constituted a potent tool
for the chemist. Mr. Teal
discussed the main fea-
tures of the Raman spec-

tra of some simple molecules and the
applications of the data, and then re-
viewed the results which have been ob-
tained during the course of studies of the
more complicated molecules.

NatTionaL Apvisory CouNCIL oN
APPLIED Puysics
During the past year several members
of the Laboratories have taken an active
part in the meetings and deliberations of
the National Advisory Council on Ap-

W. H. Harrison, Assistant Vice President of the American
Telephone and Telegraph Company, has been elected a
Director of Bell Telephone Laboratories

K. W. Waterson, Assistant Vice President of the American
Telephone and Telegraph Company, has been elected a
Director of Bell Telephone Laboratories

plied Physics. The Council was formed,
late in 1935, by the American Institute of
Physics to stimulate the application of
physics to other sciences and to industry.
O. E. Buckley, M. J. Kelly and Harvey
Fletcher are three of the thirty-nine men
forming the council. Dr. Kelly is a mem-
ber of the Executive Committee and
Chairman of the Committee on Applied
Physics. He also aided in the recasting of
the journal Physics to the Fournal of Ap-
plied Physics which appeared in the new
form with the January, 1937, issue. R. M.
Bozorth is an associate editor of this
journal. G. A. Campbell and W. Wilson
are members of a special committee which
has been appointed to assist those respon-
sible for setting up university curricula.

AT A MEETING of the
stockholders of the Lab-
oratories held on March
3, three new directors
were elected: O. E. Buck-
ley, W. H. Harrison and
Kk. W. Waterson to suc-
ceed E. H. Colpitts, Ban-
croft Gherardi and E. F,
Carter. The other direc-
tors are E. S. Bloom,
C. G. Stoll, W. F. Hos-
ford and F. B. Jewett.

Dr. Jewett addressed
the Bond Club of New
York at its regular lunch-
eon held February 19 on
the subject Science and
Research in Electrical
Communication.

E. L. Netson and H.
B. FisHER visited Wash-
ington to attend the Air
Line Safety Conference
called by the Depart-
ment of Commerce. Mr.
Nelson and D. K. Martin
also attended a meeting
of the Radio Technical
Committee for Aeronau-
tics held in connection
with this conference.

H. PrannenstIEHL and E. T. Morr-
RAM visited Hawthorne to discuss the
manufacture of new recording equipment.

F. G. Bunrenporr was in Hawthorne
on testing equipment to be used in the
production of steel tape for magnetic
recording.

H. C. Curt and W. L. Berrs visited
Dahlgren, Virginia, to conduct outdoor
tests on experimental apparatus. Mr.
Curl made several trips to Washington to
discuss matters of interest with various
Government organizations.

R. E. Coram spoke on Radio Telephony
in the Bell System before the Dover
Rotary Club on March 8.

T. E. Suea visited Washington to dis-
cuss communication problems with of-
ficials of the U. S. Navy.

E. O. Scriven and D. T. BELL spent a
day in Washington conferring with mem-
bers of the Acoustics Division of the
Bureau of Standards.

H. H. Gienn with W. V. THompson
were at Point Breeze on the development
of rubber insulated cords.

W. R. Netsser at Hawthorne conferred
with engineers of the Western Electric
Company on the manufacture and pro-
duction of the 101A induction coil which
is used in the combined telephone set.

E. W. Apams, appointed General
Patent Attorney on March 1 to suc-
ceed J. G. Roberts who retires on
May 1, graduated from
Armour Institute of
Technology in 1908 with
the Degree of B.S.E.E.
He then studied law at
the National University
Law School and obtained
his LL.B. twoyears later.
Continuing these studies,
he received the Degree of
M.P.L. at Washington
University the next year.
For the four years fol-
lowing his graduation
from Armour | Institute,
he was an Assistant Ex-
aminer in the United
States Patent Office. He
is a member of the Bar
of the District of Colum-
bia and of the State of
New York.

In 1912 Mr. Adams
entered the Patent De-
partment of the Western
Electric Company, and
from 1913 to 1916 was
in Antwerp and London
for the International
Western Electric Com-
pany. On his return from

Europe he again joined the Western
Electric Patent Department. In 1925 and
1926 another foreign assignment took
him to London and the Continent where
he prosecuted and maintained European
patents owned by the Western Electric
Company. Since then Mr. Adams has
been Assistant General Patent Attorney,
handling all phases of the Laboratories’
patent problems dealing with telephone
systems and general equipment.

A. C. WALKER, speaking on Moisture
in Textiles, took part in a Symposium on
Applied Physics at the North Carolina
meeting of the American Physical Society
on February 20. While there, he visited
the laboratories of the University of
North Carolina at Chapel Hill and of
Duke University at Durham. He also

E. W. Adams, appointed General Patent Attorney of Bell
Telephone Laboratories

spent a day at the Charlotte branch of
the Kendall Mills observing the manu-
facture of cotton cloth. On March Io, Dr.
Walker talked on Location and Distribu-
tion of Moisture in Cotton before an
A.S.T.M. committee meeting at Provi-
dence, Rhode Island.

P. NEILL discussed problems relating
to the manufacture of switchboard plugs
at Hawthorne.

ENGINEERING ROUTINES of designing
for manufacture were discussed by R. L.
Jones, O. M. Glunt, H. J. Delchamps and
H. C. Atkinson with engineers of the
General Radio Company at Cambridge,
Massachusetts.

W. Fonp1Lier while visiting the Uni-
versity of Florida at Gainesville spoke to
the senior engineering students on various
problems arising in engineering practice.

THE INSTALLATION of a trial length of
corrosion-protected cable at North Bergen,
New Jersey, was witnessed by L. S. Ford,
J. H. Gray and R. Pope.

F. E. Nrmmcke supervised the installa-
tion of a quarter-wave shunt-excited

vertical radiator at Station WSAZ,
Huntington, West Virginia. He also
supervised the installation of high fidelity
conversion parts in the 304A Radin
Transmitting Equipment at Station
WPRO, Providence.

P. C. Paguetre visited Kansas and
Colorado in connection with the trial in-
stallation of the type-J carrier system. He
also visited Dallas, Texas, to discuss
cable-terminal maintenance problems.

A. L. Fox spoke on Non-Electrical
Problems in an Electrical Industry before
the Columbus, Ohio, section of the
A.I.E.E. While in Ohio he visited the of.-
fices of the Ohio Bell Telephone Company
at Columbus and Cleveland.

R. C. and J. W. Kennarp
discussed insulator development prob-
lems at the Whitall Tatum Company’s
glass plants at Millville, New Jersey. Mr.
Dehmel later attended the meeting of
Committee D-9 on Electrical Insulating
Materials of the A.S.T.M. which was held
at Pittsburgh.

Amelia Earhart and W. C. Tinus discussing the Western Electric radio equipment
which is installed in her “laboratory” plane

E. B. Smirx of the Systems Development
Department completed thirty years of service
in the Bell System on the third of March

Jersey, to inspect the ultra-high-frequency
radio equipment being installed for the
Municipal Police Department.

F. A. Hoyt visited the Chicago offices
of the Illinois Bell Telephone Company to
discuss coin collector problems. While in
Chicago he made a trip to the Hawthorne
Works of the Western Electric Company.

H. I. Bearps.ey was at Hawthorne for
ten days on problems relating to the
manufacture of the combined handset
and of other station apparatus.

R. V. Terry visited the Warren Tele-
chron Clock Company at Ashland, Massa-
chusetts, to discuss the design of clocks
for use in telephone time bureaus.

THE MANUFACTURE and production of
new station apparatus were discussed by
H. A. Frederick, H. O. Siegmund and
J. R. Townsend with engineers at Haw-
thorne during the week of February 8.

TELEPHONE OFFICES in Floral Park,
Long Island, and Bayonne, New Jersey,
were visited by F. C. Kuch, R. B. Bauer
and W. J. Lacerte where they observed
the performance of several relays of
special design.

At Kearny, a demonstration of manu-
facturing processes for polarized relays
was witnessed by E. J. Pratt, D. E.
Branson and M. R. Purvis together with
R. J. Anspach and J. W. Harrison of the

W. Y. Lance has been with the Teletype
Corporation in Chicago discussing de-
velopment work relating to teletypewriter
apparatus.

R. H. Linpsay and J. F. Morrison
visited Stations WEAN and WPRO at
Providence to supervise the tuning of the
directional antenna arrays. Mr. Morrison
also took care of the tuning of the direc-
tional antenna arrays at radio station
Boston.

A. C. Garrecut, with Mr. Scheff of the
New Jersey Telephone Company, visited
the East Orange, New Jersey, telephone
office to obtain information relating to
projected vibration tests of panel-dial
equipment.

CERAMIC INSULATING materials were
discussed by W. A. Evans, V. L. Ronci
and K. G. Coutlee with engineers of the
American Lava Corporation at Chatta-
nooga on February 1. On the next two
days Mr. Evans and Mr. Coutlee visited
the Point Breeze plant on matters per-
taining to the manufacture of the 98A
protector block.

O. W. Towner supervised the installa-
tion of a 353E-1 (1-kilowatt) radio trans-
mitting equipment and a direct-connected
shunt-excited vertical radiator for Station
WSAN, Inc., Allentown, Pennsylvania.

T. C. Rice of the Inspection Engineering
Department completed thirty years of service
in the Bell System on the nineteenth of March

He also spent nine days at Station WHAS
of the Louisville Courier Fournal assisting
in the operation of the 306A (s0-kilowatt)
radio transmitting equipment during the
period of the recent flood emergency.

Mr. Evans and R. Burns attended
committee meetings of the A.S.T.M.
which were held at Pittsburgh. While
there Mr. Evans also visited the Stupa-
koff Laboratories.

On Fesruary 24, J. R. Townsend dis-
cussed ceramic materials with scientists
of the General Electric Company at
Schenectady.

W. Herriotr visited the Bausch and
Lomb Optical Company and the Folmer-
Graphlex Company, Rochester, New
York, on various optical and photographic
problems.

C. H. Greena.t took part in the dis-
cussion of the paper The Fatigue of Copper
Alloys which was presented at the meet-
ing of the American Institute of Mining
and Metallurgical Engineers held in New
York. With Mr. Townsend, he attended
various committee meetings of the
A.S.T.M. held in Chicago in March.

A GROUP LUNCHEON of the supervisors
of the Apparatus Development Depart-
ment was held at the Fifth Avenue Hotel

on March to. Following the luncheon,
R.L. Jones introduced O. E. Buckley who
gave a most interesting talk on Executiye
Headaches. H. C. Atkinson responded and
expressed the appreciation of the audience,
Dr. Buckley discussed some of the prob-
lems intimately associated with the func-
tioning of the Laboratories, about which
the Executive Vice President has to
worry and which are of vital interest to
those in supervisory capacity. About 180
men attended the luncheon. The com-
mittee in charge of arrangements was as
follows: W. F. Brown, H. C. Curl, P. §,
Darnell, J. B. Dixon, R. C. Koernig,
W. H. Sellew, O. A. Shann, H. D. Wilson,
and J. M. Wilson.

F. P. Wicur is at Norfolk, Virginia,
in connection with the installation of
teletypewriter line concentration unit and
associated equipment.

J. C. Crow supervised the instal-
lation of a 310B (250-watt) radio trans-
mitting equipment at Station WBAX for
J. H. Stenger, Jr., located at Wilkes-
Barre, Pennsylvania.

W. H. LicHTENBERGER attended the
coordination conference at Hawthorne on
the New St. Paul and Minneapolis toll
and dial project.

MEMBERS OF THE LABORATORIES TO WHom Patents WERE
IssuED DurinGc JANUARY AND FEBRUARY

J. W. Beyer D. W. Grant
W. M. Bishop A. J. Grossman
B. G. Bjornson C. W. Halligan
N. W. Bryant H. S. Hamilton
W. W. Carpenter A. E. Harper
R. S. Caruthers (2) H. C. Harrison
H. R. Clarke J. M. Hayward
I. E. Cole R. A. Heising (2)
W. W. Cramer L. B. Hilton
G. C. Cummings (2) _ V. L. Holdaway

To measure internal
noise, a transmitter
is carefully shielded
from vibration in
this spring-sus-
pended chamber

assignments in the Mississippi and Ohio
Valley flood area, where they were co-
operating with the telephone companies
in applying emergency power equipment.
Mr. Callahan was also in Buffalo, New
York, and West Chester, Pennsylvania,
in connection with high-speed gasoline
engine-driven generators and Mr. Sole
was in Fort Wayne, Indiana, on motor
and generator development and voltage
regulation.

H. H. Spencer visited various points
on the Toledo-South Bend cable to in-
spect the cable-carrier power plants de-
signed for this cable.

R. P. Jurson has been checking the
operation of the power equipment on the
New York to Philadelphia coaxial cable.

Durinc Fesruary the flood area in
Paducah, Kentucky, was visited by
E. W. Hancock to inspect the damage to
the Paducah central office equipment and
to assist the telephone company in plan-

W. J. Lacerre visited Hartford in
connection with a trial installation of
248-type relays for use in step-by-step
systems.

IN CONNECTION with tests on the New
York to Philadelphia coaxial circuit,
J. P. Radcliff has gone to Philadelphia
and R. L. Tambling has returned to
New York.

L. F. Porter, accompanied by F. S.
James and M. J. Stigers of the Operation
and Engineering Department of the
American Telephone and Telegraph Com-
pany, visited Pittsburgh to discuss with
engineers of the Bell Telephone Company
of Pennsylvania the proposed new toll-
tandem facilities for the Pittsburgh toll
office.

AN INVESTIGATION of crosstalk at car-
rier frequencies in lead-covered cables
was made at Point Breeze by F. W. Am-
berg, L. Hochgraf and M. A. Weaver.

Ten members of the Laboratories were
retired with pensions during 1936, making
a total of 89 receiving service or disability
pensions at the end of the year. One re-
tired member died in 1936.

Payments of accident disability bene-
fits and expenses resulting from acci-
dental injuries were lower in 1936 per
$1000 of total Laboratories’ payroll than
in any previous year. Sickness benefit
payments showed a marked increase;
more cases of over a week’s duration oc-

Fifteen active members of the Lab-
oratories died in 1936 and, in accordance
with the Plan, where eligibility to Death
Benefits existed, payments were author-
ized to their qualified beneficiaries.

In addition to benefits under the Plan,
supplementary relief payments totalling
$5,499.25 were paid to active and retired
members of the Laboratories who were in
need of special assistance during the year.

The members of the Employees’ Bene-
fit Committee are A. F. Dixon, Chairman,
E. W. Adams, A. B. Clark, J. W. Farrell,
R. L. Jones, M. J. Kelly, L. Montamat,
G. B. Thomas and W. Wilson. J. S.
Edwards is Secretary of the Committee
and D. W. Eitner is Assistant Secretary.

J. S. Epwarps, Secretary,
Employees’ Benefit Committee.
The above statement of payments
audited and found correct.
E. J. Santry, General Auditor.

Recent y E. S. Witcox, M. V.HunTER
and M. Aruck moved from Fort Worth
to San Antonio, Texas, where they will
continue high-frequency crosstalk tests
on open-wire circuits.

R. L. Kaytor has been at Phoenixville
making induction tests in connection with
broad-band systems.

R. S. Hoyt graduated from the Uni-
versity of Wisconsin in 1905 with the
degree of B.S. in Electrical Engineering.
He then spent a year at the Massachu-
setts Institute of Technology as a gradu-
ate student and assistant instructor. In
June, 1906, he joined the Engineering
Department of the American Telephone
and Telegraph Company in Boston and
there he became concerned with trans-
mission development and research. In
the 1907 move to New York, Mr. Hoyt
came to West Street to be with the Engi-
neering Department of the Western Elec-
tric Company. Two years later he con-
tinued his education at Princeton where
he received his M.S. in 1gto. Returning
to the Western Electric Company that
Summer, he worked for a year in connec-
tion with the development of various re-
peaters and on loaded lines, and then
transferred to the American Company
where he was first with the Engineering
Department and then with the Depart-
ment of Development and Research.
When the latter was consolidated with

the Laboratories in 1934, Mr. Hoyt re.
turned to West Street with the Trans-
mission Development Department.

During the thirty years of service which
he completed on February 22, Mr. Hoyt
has contributed much to the theory of
telephone transmission lines and associ-
ated apparatus, to the theory of crosstalk
and other interferences and to probability
theory with particular regard to its ap-
plication in telephone transmission engi-
neering. He has been issued twenty-one
patents and has been the author of several
papers published in the Bell System
Technical Journal.

ON THE ELEVENTH of last month Herb-
ert Vaderson completed a quarter century
of service with the Western Electric Com-
pany and the Laboratories. Mr. Vaderson
joined the Engineering Department of the
Western Electric Company in 1912 asa
draftsman in the apparatus design group.
Four years later he transferred to the
group designing and developing radio
equipment for Army and Navy purposes,
particularly for use on aircraft and on
submarine chasers.

Following the War he spent six months
at Deal Beach in the mechanical design
of the apparatus used in the first practical
demonstration of ship-to-shore radio tele-
phone. Since then Mr. Vaderson has been
principally engaged in the mechanical
design of radio broadcasting apparatus

and radio communication apparatus for
aircraft. In 1927 he participated in the
development of the radio equipment used
in the New York to Washington television
demonstration.

THE PRESENTATION of a five-star serv-
ice emblem to W. L. Heard on March 4
marks his completion of a quarter century
of service in the Western Electric Com-
pany and the Laboratories. Following his

1g11 with the degree of B.S. in Electrical
Engineering he immediately went with
the Automatic Electric Company in
Chicago. The following March he joined
the student course of the Western Elec-
tric Company at Hawthorne and then
entered the Engineering Department on
Equipment Development. In 1918 he
transferred to New York and became
intimately associated with the develop-
ment of machine switching equipment,
particularly that used in the first panel
installations such as the New York
Metropolitan Toll-Tandem and the Kan-
sas City office. He also assisted in the de-
velopment of the No. 11 manual switch-
board and various other equipment for
central office use. He also held various
supervisory positions in the equipment
group during this period.

Since 1924, as Equipment Methods En-
gineer of the Systems Development De-
partment, Mr. Heard has had charge of
all drafting work and of handling, index-
ing and distributing the tracings, specifi-
cations and drawings prepared in the
Systems group as well as quantities of
similar technical information received
from the telephone company and the
Western Electric Company for reference
purposes. Methods of handling this work
efficiently and departmental costs and
clerical work are also under the super-
vision of Mr. Heard.

R. M. Bozortu spoke on Ferromagnetic
Theory before the Communication group
of the New York Section of the American
Institute of Electrical Engineers.

OPEN-WIRE CIRCUIT crosstalk tests on
circuits involved in the trial of the
Type-J carrier system were made by John
Mallet, C. H. Gorman, Jr. and J. L.
Lindner at Stafford, Kansas.

DwRING THE MONTH of February, G. C.
Southworth spoke on the subject of Wave
Guide Transmission at McGill University,
Montreal, at the Research Laboratory of
the General Electric Company, Schenec-
tady, before the Montreal Electric Club
at luncheon and at meetings of the Engi-
neering Institute of Canada and the
American Institute of Electrical Engi-
neers that were held in Montreal and
Toronto respectively.

C. R. Burrows spoke on The Surface
Wave in Radio Propagation Over Plane
Earth before the Radio Club of America
in New York on February 11.

E. E. ScouMACHER has been elected to
serve on the Executive Committee of the
Institute of Metals Division of the Ameri-
can Institute of Mining and Metallurgical
Engineers.

J. R. Witson and H. A. PipGeon were
in Princeton, Philadelphia, Harrisburg,
and Elkton, Pennsylvania, to inspect
vacuum tubes in repeater stations.

Ar Scuenectapy, F. R. Lack, H. E.
Mendenhall and S. B. Ingram discussed
the design and manufacture of various
vacuum tubes with engineers of the
General Electric Company.

now held by members of the Laboratories: Wetherill, by E. C. Wente and
F. F. Lucas; Howe, by F. F. Lucas; Longstreth, by E. Bruce; Edison,
by F. B. Fewett; Elliott Cresson, by G. W. Elmen, C. F. Davisson and
L. H. Germer; Faraday, by F. B. Fewett; Hughes, by C. F. Davisson;
Fohn Scott, by G. W. Elmen and H. E. Ives; Royal Photographic
Society, by F. F. Lucas; Progress (S.M.P.E.), by E. C. Wente; Dudley,
by Ff. R. Townsend. Others are the Franklin Medal, by F. B. fewett; and
that recently awarded to the Laboratories as a whole by the American
Institute of the City of New York, shown in the last issue

Harvey FLETCHER attended the meet-
ing of the American Physical Society at
Duke University in Durham, North
Carolina. Later, at Troy, New York, he
spoke on The Nature of Hearing at a
convocation of Russell Sage College.

R. R. WitutaMs spoke on The Quest of
Vitamin B, before the Franklin Institute
in Philadelphia on February 17.

W. J. Ciarke attended the A.S.T.M.
Committee Dg meeting, held in Pitts-
burgh, to discuss cure tests on various
molded plastics.

R. M. Burns and S. O. Morcan
visited the New York College of Ceramics
at Alfred, New York. They also visited the
Research Laboratory of the General Elec-
tric Company in Schenectady, New York.
Mr. Morgan has been made vice-chair-
man of the Subcommittee on Mono-
graphs of the Engineering and Industrial
Research Division of the National Re-
search Council.

THE INSTALLATION of testing equip-
ment for the combined handset took
F. West, J. T. L. Brown and L. E. Krebs
to Hawthorne.

G. A. Wau. was at Hawthorne on a
study of various molded parts which are
to be used in the combined handset.

R. E. Waterman (left) examining small wood speci-
men at Gulfport test plot while G. 9. Lumsden

H. A. Larter visited several telephone
companies and distributing house shops
in the Southern and Western Areas.

H. A. Pipceon, on March 3, lectured
on Multi-Electrode Vacuum Tubes and
Beam Power Tubes in the A.1.E.E. Elec-
tronics Course.

AT THE CONVENTION of the Op-
tical Society of America held at
Corning, New York, on March 4
to 6, H. E. Ives presented a
paper entitled Graphical Exposi-
tion of the Michelson-Morley Ex-
periment. He also presented a
paper entitled The Optical Con-
stants of Sodium with H. B.
Briggs as co-author.

On January 27, M. E. Strieby
gave an illustrated talk on co-
axial cable systems before the
Treasury Luncheon Club com-
posed of members of the financial
departments of the Bell System
companies in the Metropolitan
district. He spoke on Quantity
Production of Toll Circuits.

Kart K. Darrow has been elected to the
Council of the French Physical Society.

L. H. Germer, on March 12, spoke be-
fore the Metropolitan Section of the
American Physical Society on Structure
of Organic Crystals.

PLATING PROBLEMS made it necessary
for C. L. Hippensteel to visit the Western
Electric Company at Hawthorne. Later
he presented R. M. Burns’ discussion of
the paper entitled Principles of Corrosion
Testing presented before the American
Society for Testing Materials in Chicago.

F. M. Ryan spoke on Radio Reflections
before the March meeting of the Collo-
quium held at the Deal Radio Laboratory.

A. M. SKELLeTT addressed the Ama-
teur Astronomers Association at the
American Museum of Natural History in
New York, March 3, on The Solar Corona.

FouR-STAR SERVICE emblems signifying
the completion of twenty years of service
with the Bell System were awarded to
nine members of the Laboratories during
the month of March. In the Apparatus De-
velopment Department, E. H. Chatterton
completed twenty years’ service on the
sixteenth, L. P. Collins on the twenty-
sixth and Michael O’Connell on the
twelfth; in the Research Department,
J. J. Curley on the twenty-eighth; in the
Systems Development Department, J. W.
Woodard on the second; in the General
Service Department, Angeline McDer-
mott on the twenty-first; in the Plant De-
partment, N. R. Zucconi on the twenty-
third; and in the Patent Department
M. R. McKenney on the twelfth and
C. A. Sprague on the fourteenth.

billed on a message basis. To
record this usage as many as 10,000
individual message registers may be
mounted on racks in each central of-
fice. The monthly job of recording the
readings of these registers requires
considerable time and effort. For
many years it was accomplished uni-
versally by sight-reading routines
which varied in details but usually in-
volved sending teams of two girls
each into the terminal rooms during
the night hours.

In an effort to develop other and
better means for doing the job, cam-
eras of special design have been made
to photograph the registers. The one
now used in a few of the largest cities,
Figure 1, is a manually operated
camera which has a special hood in
front to fit against the registers photo-
graphed. Inside of the hood
are four 50 c.p. 24-volt lamps
to provide illumination. The
records are made on sensitized
paper of high photographic
speed and contrast which is
wound on a_wooden-cored
spool with metal ends and pro-
tected by a heavy opaque
leader and trailer. The spacing
of the sensitized paper and set-
ting of the shutter are done
simultaneously by operating
the winding handle and the
exposure is made by pressing
a finger release located at the
side of the camera. Ten regis-

ters are recorded at a time and since
each spool of sensitized paper takes
100 exposures, space for photographing
1000 registers per loading is available.

When the recordings are made the
camera hood is adjusted against the
upper left group of ten registers. After
the first exposure, turning the hand
crank resets the camera and then a
record is made of the adjacent block of
ten registers. This operation is re-
peated one hundred times after which
the camera is unloaded and the spool
sealed and sent to the laboratory for
development. It is then ready for the
Accounting Department. Figure 2

It was found that this camera could
be improved from the standpoint of
ease of handling and speed of opera-
tion since much time is lost in the
manual operation of hand cranking

Fig. 1—Photographic records of message register
readings are now made in some exchanges with a

Fig. 2—The present message register camera photographs ten registers at a time

between each exposure. Accordingly,
a new camera shown in Figure 3 has
been developed in which a small uni-
versal motor is used instead of the
hand to move the sensitized paper,
control the illuminating lamps, and
set the shutter. Twenty-five registers
are photographed at a time, thus re-
quiring only 40 exposures per 1000
registers. A single switch controls the
entire action of the camera and it
operates on either 110 volts ac or dc,
which is supplied through a cord with
terminal plug mounted flush in the side
of the camera. The body of the camera
is made of sheet duralumin and the
exterior surfaces are lacquered black.

A projecting hood rests
against the register cover as in
the previous design. I]lumina-
tion is provided by four s0-
candlepower double-filament
automobile lamps mounted
two on each side of the camera
under removable protecting
covers. Condensing lenses are
placed immediately in front of
the lamps to increase the il-
lumination at the plane of the
register and a vignetting de-
vice serves to blend the illumi-
nation from the two sides of
the camera over the central

section of the area photographed.
Four mirrors of chromium-plated
metal line the interior of the project-
ing hood. These serve to build up
illumination at the sides of the pic-
ture area and to insure proper light-
ing of numbers located near the edges
of the picture. A mirror inclined
at 45° near the lens deflects the
light toward the base of the camera
where the sensitized paper is located.
A large section of the back cover ex-
tending from the loading chamber to
the top of the camera is removable to
give access to the lens, shutter and
inclined mirror.

the sensitized paper, controls the illuminating
lamps and sets the shutter

Figure 5, is covered by a light-tight
door for loading and unloading. The
roll of unexposed sensitized paper is
mounted at the left-hand side of the
chamber. It passes under an idler
roller and around the drum at the left
in front. This drum has a toothed
sprocket mounted immediately below
the spool to measure the advance of
the sensitized paper for each exposure.
It is then drawn across the exposure
aperture which is parallel to the base
of the camera and wound onto the
take-up roller shown in the right-hand
section of the loading chamber. The
operator knows when the sensitized
paper is in position for the first ex-
posure and again when the last frame
is in place by the lighting of a minia-
ture bulb behind a small red window
in the camera. Cut-outs in the edge of
the sensitized paper actuate the cir-
cuit which controls this lamp.

The mechanism which transmits
power to the sensitized paper spools
and to the measuring roller also con-
trols the current to the lamps used to
illuminate the registers. These lamps
are lighted a very short time before

the actual exposure is made and
turned. off immediately afterward.
This decreases the duration of ex-
posure to approximately a third of
the time required for the full cycle of
camera operations and materially re-
duces the effect of heat from the
lamps. The torque-voltage charac-
teristics of the motor are such that
any variation in line voltage auto-
matically changes the exposure. If the
line voltage is high, the lamps burn
more brilliantly but the motor speed
will then increase so that the lengths

of the exposure portion of the cycle
will be correspondingly shortened and
over-exposure avoided. On the other
hand, if the line voltage is low, the
lessened intensity of illumination is
compensated for by a lower motor
speed which prolongs the exposure.
Records made with the new camera
are shown in Figure 6.

The operating mechanism is
mounted as a removable self-con-
tained unit located behind the plate
to which the motor and gear box are
attached. Power from the drive motor

is transmitted through reduction gears
to the pawl which controls the spacing
roller, to the shutter, the toggle
switches used to operate the lamps
and motor, and to a precision clutch
member which extends into the load-
ing chamber to control the take-up
spool. All four of the lamps in the
camera are operated in series and a
fixed resistance is added to reduce the

This new camera is of relatively
simple construction and is ruggedly
built. Endurance tests, involving
thousands of operations, have proven
its ability to perform satisfactorily
under practical conditions of use and
with considerable saving in time over
the previous design.

Fig. 6—The new message register camera photographs twenty-five registers at a time

and higher frequencies has made
it necessary to design impedance-
measuring equipment for a precision
over this extended range, comparable
to that obtainable in the audio and
lower-carrier ranges. For this purpose,
the familiar alternating-current
Wheatstone bridge* was refined to
meet the severe requirements imposed
by the higher frequencies. While es-
sentially the same as other a-c im-
pedance bridges in circuit arrange-
ment, it differs from them in the care
taken to secure constancy of all resid-
ual impedances over a very wide
frequency range, thorough shielding,
and accurate circuit balances. An in-
~ *REcoRD, Fanuary, 1932, p. 173.

teresting innevation is the use of
coaxial plugs and jacks for connecting
to the standard impedances, to the un-
known impedance and to the oscil-
lator and detector.

The circuit for the new bridge is
shown schematically in Figure 1. It
consists primarily of a pair of double-
shielded ratio arms, repeating coils for
the oscillator and detector, and a set of
six coaxial jacks by which the de-
tector, oscillator, and the standard
and test impedances are connected.
These components are assembled on a
seven by sixteen inch panel, and en-
closed in an aluminum housing, which
serves as a shield.

A photograph of this balance unit
from the rear, with the covers re-
moved from the double shielded ratio

arms, is shown in Figure 2. The ratio
arms, each of 75 ohms, employ the
woven-wire* resistor element, which
is ideally suited for the purpose be-
cause of its very small distributed
inductance and capacitance. They
maintain their impedance balance or
ratio to within one one-hundredth of

unit in mechanical layout, in wiring,
and in the disposition of the ground
admittance of the elements. The elec.
trical symmetry obviates many of the
errors that are peculiar to high-fre-
quency measurements.

Two impedance standards have
been designed for use with the new
balance unit. One is a six-dial
resistance standard and the
other an adjustable capaci-
tance standard. Both are
equipped with coaxial jacks to
permit them to be readily con-
nected to the balance unit in

one per cent for resistance and to a
thousandth of a microhenry for in-
ductance, over the entire frequency
range from Io to 5000 kilocycles.

The double-shielded repeating coils,
which serve to isolate the bridge cir-
cuit electrostatically from the power
source and the detector circuits, are
scarcely less important than the ratio
arms in their contribution to the satis-
factory performance of the bridge.
With an impedance ratio of one to one,
they are designed and constructed with
special care to insure a low value of
intershield capacitance, and to mini-
mize the capacitance between the ele-
ments separated by the ground shield.

As is partially evident in Figure 2,
a very high degree of symmetry is
maintained throughout the balance
~ *RECORD, January, 1935, p- 136.

The resistance standard,
Figure 3, is similar to the six-
dial rotor-decade already de-
scribed in the Recorp.* The
resistors are mounted in drums,
which are rotated between fixed
brushes so that only one re-
sistor unit per decade is in the
circuit at a time. The three
larger decades employ resistors
of the woven-wire type. In each of the
three smaller decades, the resistor ele-
ments are made to have as nearly as
possible identical inductance residuals,
so that the total inductance of the
bridge is maintained substantially
constant for any setting.

The capacitance standard has a
rotor-decade of mica condensers with
step values of 1000 micro-microfarads
and a special two-dial air condenser.
One of the component air condensers
has step values of 100 wuf and the
other is continuously variable over a
range of 110 wuf. The mica condenser
is similar to the resistance decades in
inserting only one unit in the circuit at
a time. This arrangement not only
minimizes stray internal capacitances,
but keeps the series inductance of the
~ *RECORD, January, 1935, p. 136.

Fig. 2—Thorough double-shielding and symmetrical arrangement are featured in the
balance unit of the five-megacycle impedance bridge

leads and wiring to a small constant
value which may be compensated by
adding an equal inductance in the op-
posite arm of the bridge. The complete
capacitance standard removed from
its case is shown in Figure 4, where
the mica decade is at the left.

The air condenser unit, which is of
exceptionally rugged design, has a
single stator that is common to two
rotors. Self-adjusting bearings are used
on the rotors to compensate for wear

Fig. 3—The resistance standard differs from others of the
same type chiefly in the provision of coaxial jacks and in the
care taken to reduce and equalize-the inductance and capact-

and also to assure a low electrical con-
tact resistance in the connections to
the rotors. The stator is supported on
three ceramic spheres, which minimize
leakage by providing what are essen-
tially point contacts with the frame,
and which permit the stator plates of
the condenser unit to be accurately
aligned with those of the rotor.

The larger dial has a click detent
mechanism arranged to stop the rotor
at 100 uyuf intervals as the dial is
turned. The detents
are individually ad-
justable so that the re-
sulting steps may be
made to agree with the
nominal value to within
+o.1 pwuf. Settings
are reproducible to
within + .03 uuf. The
continuously variable
dial, at the right of
Figure 4, carries an en-
gine-engraved scale
with a vernier that al-
lows direct reading to
within 0.1 pyf.

of the condenser to better than «1
mmf, it is essential when measuring
high impedances having a large ratio
of reactance to resistance to be able
to adjust the condenser with much
greater precision. For this purpose a

slow motion device operating on the
main dial of the condenser has been
provided which permits easy adjust-
ment to within .co2 Rapid pre-
liminary adjustment to within 1 yyuf
may be made by means of the large
knob on the condenser shaft in the
usual manner, and as smoothly as
though the slow motion
device were absent.

A novel feature of
the bridge is the use of
equal-length coaxial
cords for connecting
the standard and un-
known impedances to hi
the balance unit. In |
addition a small ter- |
minal unit, fitted with - I
coaxial jacks, is plugged
to the extremity of the
leads for the test im-

pedance to balance the residual im-
pedances of the standards. In this way
the symmetry of the bridge network
is extended to the unknown imped-
ance, and the uncertainty and the in-
convenience of corrections due to the
use of random leads are
avoided. Moreover,
since the potential drop
in the sheath conductor
of the coaxial leads is
practically nil, the
shields of the standards
and of the unknown
impedance are brought
to the same potentiai
as that of the bridge
ground.

The balance unit is
arranged for both
grounded and bal-
anced-to-ground meas-
urements; the switch
just above the bottom
corner of the bridge in
Figure 1 is closed for
grounded measurements and left open
for balanced-to-ground measurements.
For grounded measurements only the
upper of the two jacks on each side
and a single cord are used to connect
the bridge to the standards and to the
unknown. Such an arrangement is
shown schematically in Figure 5. A

photograph of such a
set-up is given in Fig-
ure 6. For balanced-to-
ground measurements
two cords are used from
each side of the balance
unit, and the standards
used, although similar
to those used for
grounded measure-
ments, have elements
that are symmetrical
with respect to ground.

Fig. 6—The terminating unit is in the form of a small
cylinder with binding posts to which the unknown is attached

above, the widest range is obtained
with the parallel connection, where
capacitances from practically zero up
to .o1 microfarad, with a wide range
of power factor, may be measured.
Inductances that can be resonated
within this capacitance range may be
measured also, provided the detector
has adequate discrimination against
harmonics originating in the power
source. An inductive standard of suit-
able range may be substituted for the
capacitance where it is undesirable to
employ resonance methods.

Bell System, are attached to
cords having usually three conductors,
as shown in the accompanying photo-
graph. One conductor runs to the tip
of the plug, another to the sleeve or
main body of the plug, and the third
to the ring—a small metallic band
separated from the dead collar and
sleeve by narrow segments of insula-
tion. In assembling these cords and
plugs in the Western Electric Shops,
small metal cord tips are crimped onto
the tip and ring conductors as al-
ready described in the Recorp.* The

sleeve conductor is turned back over
the main body of the cord which is
threaded into the cord end of the plug
thus making contact with the metallic
body of the plug. Small screws fasten
the cord tips to the terminals in the
plug, and the outer shell is slipped
over the assembled plug and fastened
in place.

In service, wear on cords first be-
comes noticeable on the braid just
back of the plug, where the greatest
and most frequent bending occurs.
Continued use of the cord would re-
sult ultimately in serious damage to
the insulation and possibly breakage
of the conductors, but the warning

given by the fraying of the outer
braiding permits repair long before
actual failure. Such frayed cords are
repaired by cutting the cord a short
distance back of the plug, beyond the
place where the braiding is damaged,

and reconnecting it to
the plug. These repairs
are often made in the
central office where
conditions do not war-
rant the use of the
heavy crimping ma-
chine used for apply-
ing the solderless cord
tips at the manufac-
turing plant. Until re-
cently it was the prac-
tice to pierce the insu-
lation with a special
hand tool like a pair of
pliers, and push the
terminal screw through the hole. This
method had several shortcomings and
investigations were started to provide
economical ways and means of placing
solderless cord tips on repaired cords
as a maintenance operation by the
plant forces. The outcome of this in-
vestigation was the development of
the No. 444-A tool which is mounted
on the cord repair table, as shown in
the photograph at the top of the
opposite page.

tool employs a lever operated cam.
This moves the dies rapidly at the
beginning of the operation, when little
pressure is required, and more slowly
as the pressure builds up. The lever is
fairly long and massive with a heavy

Fig. 1—Bottom: an assembled cord and plug with insulating
sleeve or shell removed to show method of fastening conductors;
top and center: plug without cord and with cord end cut in

handle, which gives it a flywheel ac-
tion as it is swung rapidly through one
complete revolution. Pressures esti-
mated to be in the neighborhood of
1000 pounds are required to apply a
solderless cord tip satisfactorily, and
this portable tool so balances opposing
forces that only small unbalanced
components react on the light port-
able table itself.

In operation the outer braid and
tinsel conductor are cut back and the
tip and ring conductors are placed in
the gauge block on top of the machine.
With cutting pliers each is
then cut to its proper length.
A tip is placed in one of the
cavities of the die and a cord
conductor is placed in it. The
handle, which has been hang-
ing vertically downward, is
then brought up with an ac-
celerated motion and turned
rapidly through one complete
revolution. During the down-
ward part of the stroke, par-

ticularly during the last quarter when
the greatest pressure is applied, the
flywheel action of the handle adds a
very appreciable amount to the actual
force applied by hand. At the bottom
of the stroke the cam is cut back to re-
lease the die, which is pushed back
into its normal open position by a

gauge block are shown in Figure 2,
With this new apparatus solderless
cord tips may be rapidly applied with-
out removing the cord from the
switchboard. The repaired cord will
be essentially the same in its terminal
connections as a new one. The cords
are long enough to allow several repairs
to be made before being discarded,

Assembling the elements of an experimental vacuum tube in the
Tube Development Laboratory

E distributing frame has been,
in one form or another, a part
of the telephone system since
the early days. It carries terminals for
the incoming lines on one side and
terminals connecting to the central
ofice apparatus on the other side.
Cross-connecting wires between term-
inals on the two sides of the frame
allow flexibility in associating cable
pairs with the office apparatus so that,
for example, a subscriber may move
within the office area without having
his number changed. Where the wires
change direction, their side pull is
carried by insulated rings.

The old No. 1 and No. 2 rings, which
differ from each other only in the size
of the rings, consist of an iron rod three-
eighths inch in diameter, threaded on
one end and bent to form an open
circular ring. The threaded portion is
used to mount the ring on the frame,

while the ring portion with which the
cross-connection wire comes in contact
is insulated by a hard rubber covering.
Rings of this type have been in use for
forty years. Old and new rings,
mounted side by side in a central office
during the field trial, are shown above.

The new 9A ring, which was de-
veloped to replace both the No. 1 and
No. 2 rings in new equipment, consists
of a closed cast iron ring intermediate
in size between the No. 1 and No. 2
rings. The whole ring is insulated with
a coating of vitreous enamel. A shoulder
engages the frame so that the ring is
held in exact position by a single bolt.

The 9A ring offers the advantages
of greater strength and rigidity than
the old ring, fixed alignment in the
frame and a hard, smooth insulating
finish which will be practically im-
pervious to wear and will not abrade
the cross-connection wire.

F. R. Dennis received the B.S. degree
in Electrical Engineering from the State
College of Washington in 1929 and joined
the Apparatus Development Department
of the Laboratories in September of that
year. A considerable part of his time for
the first two years was spent making im-
pedance and attenuation measurements
on cables for carrier telephony. It became
evident that the attenuation measuring
sets then available were inadequate at the
higher frequencies where measurements
were beginning to be required. He there-
fore undertook the development of at-
tenuators and attenuation measuring cir-
cuits which would maintain high accuracy
over the radio frequency range. For the
past year and a half the group with which
he is connected has been charged with the
development of oscillators, detectors and
other vacuum tube apparatus. His present

work is partly of this nature and partly
continuation of work on attenuation
measuring circuits and attenuation stand-
ards suitable for checking the accuracy of
shop sets which operate in the radio fre-
quency range.

and joined the Engineering Department
of the Western Electric Company in 1917,
During the next year he was in the
drafting group working on various de-
vices for detecting airplanes and sub-
marines. He then transferred to the
Apparatus Development Department,
where, in addition to developing ap-
paratus for the above uses, he designed
radio apparatus for the Signal Corps.
Since then he has remained with the
same group and has been in charge of
the development of a wide variety of
apparatus for use in the telephone plant.

C. H. Younc received the degree of
B.S. in Electrical Engineering from the
University of Michigan in 1927. He at
once joined the Technical Staff of the
Laboratories where, with the electrical
measurements group of the Apparatus
Development Department, he has en-
gaged in the development of precise im-
pedance measuring equipment and resist-
ance standards with low time constants.

J. M. Barstow was graduated from
Washburn College in 1923 with the B.S.
degree. He then took up graduate work at
the University of Kansas and received his
M.S. degree the following year. Following

this he was employed for three years as an
instructor in Physics at the Kansas State
Agricultural College. In June, 1927, he be-
came a member of the Department of De-
velopment and Research of the American
Telephone and Telegraph Company, his
major work being on noise problems. As a
member of Project Committee 1B of the
Joint Subcommittee on Development and
Research, Edison Electric Institute and
Bell System he has conducted judgment
and articulation tests on the interfering
effects of various sorts of noise and has
been instrumental in devising noise
measuring devices. As secretary of the
Technical Committee on Sound Levels
and Sound Level Meters, he took part in
setting up the American Tentative Stand-

ards for Sound Level Meters approved
by the American Standards Association
in February, 1936.

AFTER GRADUATION by Massachusetts
Institute of Technology in 1914, H. A.
Affel returned for two years as a research
assistant in electrical engineering. In 1916
he joined the engineering staff of the
American Telephone and Telegraph Com-
pany, and with the organization of the
Department of Development and Re-
search in 1919 became associated with its
Transmission Development group, where
he engaged in studies of carrier and radio
transmission. In 1929 he transferred to
the Toll Transmission group where his
work included among other things the
design of repeaters, program circuits, and
carrier systems. With the transfer of the
Development and Research Department
to the Laboratories in 1934, Mr. Affel re-
mained with the same group. Now as
Toll Transmission Development Direc-
tor, he has been placed in charge of the
entire department.

ern Electric Engineering Department
where he worked on electrolytic con-
densers and later on household appliances
and farm equipment, at that time a
merchandise activity of Western Electric.

paratus Development Department he be-
came a member of the group responsible
for inside wires and switchboard cables.
Here he has been concerned with a num-
ber of related problems such as the design
of apparatus for humidity studies and for
investigation of central office ventilation.
On account of its close association with
distributing frame wire, the 9A ring,

WHILE AN undergraduate at the Uni-
versity of Pittsburgh from 1914 to 1917,
W. Herriott engaged in astronomical re-
search at the Allegheny Observatory.
This was followed from 1917 until 1920 by
research in astronomical and aerial pho-
tography at the Eastman Kodak Com-

pany. Between 1920 and 1925 he was en-
gaged in the development of optical
apparatus for microscopy, photography
and motion pictures with the Bausch and
Lomb Optical Company. During the fol-
lowing three years he was in charge of
the Scientific Department of the Fair-
child Aerial Camera Corporation. In 1928
he joined the Engineering Department of
the Electrical Research Products, Inc., to
work on optical and photographic prob-
lems associated with sound pictures. Mr.
Herriott came to the Laboratories in 1929
and continued work in sound pictures
until October, 1936. Then he transferred
to the Materials Group of the Electrome-
chanical Division of the Telephone Appa-
ratus Development Department.

Bell Laboratories Record 1937-04: Vol 15 Iss 8