THE CO\ER: It. Behler (left) and J. Novotny discussing
master layouts of printed circuits (see opposite page).

Tlie BELL LABORATORIES RECORD is published monthly by Bell Telephone
Laboratories, Incorporated, 463 West Street, New 1 ork 14, N. 1., M. J. KELLY,
President; W. C. Toole, Secretary; and G. B. Small. Treasurer. Subscriptions:
$2.00 per \ear*, Foreign, $2.60 per year. Cheeks should he made payable to
Bell Laboratories Record and addressed to the Circulation Manager. Printed
in l , S. A. (§) Bell Telephone Laboratories. Incorporated. 1958.

EDITORIAL BOARD
F. J. Singer, Chairman
J. A. Ilornbeck
F. A. Korn
E. T. Mottram
R. J. Nossaman
W. E. Reichle
A. H. White

l util recently, the extent to which complex electronic equipment could he
decreased in size as a result of the new family of miniature devices — tran¬
sistors, thermistors, semiconductor diodes — was limited to a large degree
by the physical space required for conventional wiring. This limitation has
been largely overcome in many applications by the growing use of printed-
circuit techniques. Considerable development work has been done in this
area at the Laboratories, particularly in fundamental studies on raw materi¬
als, and the physical and electrical characteristics of printed wiring.

The traditional method of building electronic
equipment is being challenged today more than at
any time in the history of the industry. The impetus
stems from the invention of the transistor, which
opened a new era of electronic devices, and from
the rising costs of fabricating and maintaining the
complex electronic systems planned for telephone,
military and data-handling systems.

To cope with this situation, the designers must
adopt more efficient concepts which will result in
equipment that is dependable, inexpensive, simple
to build and easy to maintain. One concept steadily
gaining recognition in new development projects
is the “unit assembly’’ or “modular” technique with
“printed circuits” as the basic building block. With
this technique, the highly repetitive low-power
and low-voltage circuitry prevalent in most new
electronic systems is divided and packaged into
logical groups which perform specific functions,
such as voltage amplification, binary counting, and
so on. Each of these may be a module consisting of
a single printed-wiring board which contains all of
the components, as illustrated in Figures 1 and 2, or
it mav consist of a printed interconnecting wiring
board and several submodules as illustrated in Fig¬

ure 3. In either case, the printed wiring board is the
basic unit of the system.

The term “printed wiring” implies that the con¬
ductors which interconnect conventional electrical
components are produced on an insulating base by
any process which does not employ conventional
wiring. “Printed circuits,” often used interchange¬
ably with “printed wiring,” implies that resistors,
capacitors and inductors are also printed.

There are at least twenty known methods of pro¬
ducing printed wiring. Among these, six of the most
commonly used may be generally classified as the
“printed or painted wire,” the “plated wire,” the
“embossed wire,” the “stamped wire,” the “transfer”
and the “etched wire” processes.

In the printed or painted wire processes, finely
divided silver or copper dispersed in a lacquer or
ink carrier is applied to an insulating board by
spraying or brushing through a stencil or by offset
printing. The printed path is then made conductive
by removing the organic carrier which separates
the metallic particles. In the case of ceramic boards,
this is done by the application of heat. Where plas¬
tics are used, volatile solvents are normally incor¬
porated in the carrier; also a small amount of

Fig, 1 Printed circuit boards used to intercon¬
nect com ponents of a single module as used in the
amplifier circuits of video transmission equipment .

residual resin hinder provides the necessary ad¬
hesion between the metallic particles and the base.

A plated wire board is produced by depositing
a conductive pattern oil an insulating material by
chemical reduction, electroplating or a combination
of both. There are several variations of this process
which are used primarily where it is desired to con¬
tinue the printed wiring through a hole or around
a molded contour.

Embossed \\ ire boards are produced bv placing
a copper foil over a laminated insulating board and
depressing the conductor pattern into the board
with a heated die. The unwanted portion of the
foil is removed by a mechanical surface-abrading
operation which leaves the conductors imbedded
in the board.

Stamped wiring is similar to embossed wiring ex¬
cept that a “dinking die” is used: this simultaneously
cuts the wiring pattern from the foil and places it
on the surface of the insulating board. The conduc¬
tors are usually made to adhere to the board in a
secondary pressing operation.

In the transfer process, a mirror image of the
printed w iring is formed on the surface of a car¬
rier sheet by electroplating, etching or stamping.
This image is transferred to the insulator by a
subsequent pressing operation.

Etched wiring, which employs many of the tech¬
niques familiar to the graphic arts industry, is by
far the most popular of the currently used methods.
Most of the mechanics of this type of manufacturing
are well established, and the copper-clad plastic
raw materials had been under development by the
laminating industry for several years prior to the
full scale emergence of printed wiring. The process
is adaptable to development type work where it is

desirable to obtain small quantities of a large variety
of circuit patterns within a short time. These are
often used for laboratory development or studv.

The photo-etch process originates with an en¬
larged layout of the conductor pattern. This draw¬
ing is called a “master" and is produced bv applying
precut strips of opaque, nonreflecting, pressure-sen¬
sitive tape onto a dimensionally stable Mylar film.
The reverse side of this translucent film is printed
w ith a grid coordinate system which is used as a
guide by the draftsman for laying out the conduc¬
tors in modular dimensions. Thus, each hole for a
component mounting lead and each conductor is
designated bv cartesian coordinates.

The master is photographed and reduced to ac¬
tual size with a precision copy camera. Anv draft
ing errors on the master are thus minimized on the
resulting negative, which may then be used to pro¬
duce the conductor pattern on the circuit board.
This negative is used to produce silk screens or off¬
set printing plates which in turn are used to print
the pattern on the board. The circuit board is a
copper-clad laminate, generally' one sixteenth of an
inch thick, from which portions of copper are etched
a wav to leave a pattern of conductive lines.

With the photo-engraving technique, a photo¬
sensitive “resist” (acid resistant lacquer or enamel)
is applied to each copper surface from which the
circuit is to be formed. The negative of the con¬
ductor pattern is placed over the sensitized surface
and exposed to ultraviolet light which renders the
conductor pattern insoluble in the developer. The
areas protected from the light by the opaque por¬
tions of the negative remain soluble so that the
resist is removed in the developer. The unprotected
areas of copper are then etched away to leave a

Fig. 2- Printed circuit board used to interconnect
the components of a single die-cast module unit.

After the resist material is removed and the board
is cleaned, a thin coating of solder is applied to the
conductors to provide protection during storage
and to enhance solderability during subsequent
assembling operations. This coating is applied by a
“roller-coating” process wherein the fluxed board
is passed through two rollers. One of these is tinned
and partially immersed in molten solder; the other
applies uniform pressure between the board and
the tinned roller to insure that there is good wetting
of the conductors.

r ig. 3 — An example of printed H iring used to interconnect
several sub-modules on a single board as used in a frau¬
ds! orized high-speed digital computer circuit.

point-to-point wiring. In addition, it is possible
to incorporate small amounts of capacitance, in¬
ductance and shielding directly on the board and
thus reduce the required amount of cabling and
shielded wires. The size reduction is compounded
in the over-all system by reducing the need for
heavy structures to support the many heavv metal
chassis and cables. This is illustrated in Figure 4
by a printed coaxial line on a circuit board for a
transistor video amplifier.

Maintenance of electronic svstems is improved
by the use of printed-circuit unit assemblies which
can be replaced much as electron tubes are replaced,
and can be checked as functional units. Also, the
time required for trouble shooting individual cir¬
cuits is reduced because the circuit path is dis-
tinctlv outlined in the printed-wiring pattern.

Reliability is improved in several ways. The de¬
signer is given greater control of the precise de¬
ployment of conductors in the manufactured units.
This minimizes the possibilities of shorting and
varying stray capacitances, and results in a more

Fig. 4 — Coaxial line (arroics) produced by printed circuit
techniques on transistorized video amplifier .

uniform product from which wiring errors have
been virtually eliminated. In addition, the num¬
ber of soldered connections can be greatly reduced,
since it is possible to have any number of conductors
emanating from a single point, and three or more
components can be joined with a single continuous
strip of copper.

The development of printed circuits has consid¬
erably advanced the art of automatic or mechanical
assembly of electronic equipment. Unlike the con¬
ventional circuits of ten years ago with their maze
of insulated wires, stand-offs and mounting termi¬
nals, hand wrapped and soldered joints and difficult
assembly sequences, the printed-circuit board is
readily adapted to large-quantity production and is
ideally suited to mechanical insertion of compo¬
nents and mass soldering. Even in those instances
where mechanical assembly is not feasible for ec¬
onomic reasons, the same design considerations re¬
sult in units which are easier to assemble manually.

There are some disadvantages; special precautions
must be taken, for example, to extend the field of
application beyond that of low-power circuits. In
this regard, systems designed to use printed circuits
have a far greater proportion of insulating material
than is normally encountered in conventionally
wired equipment. This puts the burden of respon¬
sibility for satisfactory operation on the insulating
materials, adhesives, conductor finishes and pro¬
tective coatings associated with the printed-circuit
board. Except for the metallic finish and some
ceramic bases, most of the materials used are or¬
ganic plastics. High temperature is by far the most
ruinous environment for these materials — in fact,

Fig. 5 — Rotary switches prod it rod by printed circuit tech¬
niques; right „ time sharing and left , zero set.

some of the present materials arc 1 combustible.
Hence, special precautions must be taken to con¬
trol heat dissipation.

Insulation resistance is also extremely important
in the development and use of printed circuits.
On a conventional plastic terminal board, the leak¬
age path is governed bv the spacing between termi¬
nals, since the effects of the strap wires are usually
negligible. Conductors on a printed-circuit board,
however, are in direct contact with the insulating
base throughout their entire length. Thus, the leak¬
age between two adjacent parallel conductors may
be appreciable. It is, therefore, important to investi¬
gate this condition early in the design stage, and
to employ materials which will insure proper per¬
formance under varying conditions of temperature
and humiditv.

Ionic contamination of the board during etching
or plating, and staining of the surfaces by perspira¬
tion during handling, may result in a malfunction.
This is due to corrosion or high leakage if the as¬
sembled unit is placed in a humid environment.
Thus, it is necessary to cleanse the board thoroughly
and to coat the surfaces with some type 1 of insulat¬
ing material. In addition, some plating solutions
and improper soldering methods can destroy the
bond and separate the printed conductor from the
insulating base. Therefore, special soldering pre¬
cautions must be exercised when replacing com¬
ponents during servicing.

The Laboratories has concentrated its efforts on
fundamental studies of raw materials, the physical
and electrical characteristics of printed wiring
under various environments, and the exploration
of methods for fabricating high-quality printed wir¬
ing. This was done to learn more about the capa¬
bilities of the materials and the processes so that
realistic specifications could be established to in¬

sure a quality level consistent with the design in¬
tent of the Laboratories.

This program resulted in the development of a
series of specifications, one of which contains pro¬
cedures for testing the critical parameters of the
base material or of the finished printed circuit.
One test is for insulation resistance, another deter¬
mines moisture sorption, a third gives a measure
of adherence of the copper to the insulator and a
fourth indicates the materials’ resistance to blister¬
ing when subjected to soldering temperatures. Sev¬
eral specimens for each test are printed on one
large panel in a manner which takes into account
variations in properties due to orientation.

Contamination of the board due to processing
has been virtually eliminated in a process called the
Applique Method which was invented by the late
E. E. Franz of the Laboratories. It is a transfer
process wherein the raw materials consist of a com¬
posite sheet of aluminum and copper foil bonded
together with a pressure-sensitive adhesive and a
fully cured plastic laminate sheet. The exposed
copper surface is treated with a partially cured
thermosetting adhesive. Then the conductor pat¬
tern is cut from the copper foil bv a dinking process
in such a manner that the aluminum foil is not
severed. Tin 1 unwanted portions are stripped from
the aluminum. This aluminum carrier is then placed
on the surface of an insulating laminate, and a
laminating press is used to bond the conductors
firmlv to the plastic sheet. The final operation is to
strip off the aluminum carrier and clean the ad¬
hesive off the surface of the conductors.

The dinking die used in this process is prepared
bv photoengraving from a hard brass plate and
then chrome plating the cutting edges to extend
the life of the tool. Thus it is inexpensive and flexi¬
ble to changes in circuitry. It is also adaptable to
continuous processing which is necessary for any
automated production system.

Allied with the problem of degradation of plastic-
base printed circuits due to heat and long-term
aging, the Laboratories is currently studying several
processes for producing reliable inexpensive printed
circuits on ceramic-base materials. One of these
has been developed for producing a spiral inductor
with conductors ten thousandths of an inch wide,
spaced at ten thousandths of an inch. The require¬
ments made it necessary to develop a process which
did not relv on firing techniques and did not result
in residual nonvolatile components.

Although these processes have been used pri¬
marily for printed wiring, thev are bv no means

limited to this application. There is an increasing
number of applications in the design of switches,
commutators, coding discs and electrical com¬
ponents. Complicated rotary and sliding switches
can be produced by those means at lower cost be¬
cause of the photoengraving technique. Also, the
development of flush circuits, wherein the surface
of the conductor and the insulator are in the same
plane, has made possible a considerable smoother
wiping surface for high-speed brushes. This re¬
duces the hazard of brush bounce which results
in erroneous switching.

An example of the application of the printed
circuitry to components is an autotransformer w hich
can be placed inside a cathode-rav tube as illus¬
trated in the photograph on page 117. The con¬
struction, consisting of a series of flat printed in¬
ductors on ceramic discs, is capable of withstand¬
ing the high degassing temperatures and the cvclic
temperatures of the tube during normal operation.
Use of this autotransformer would remove the high
potential connections from the exterior of the tube
and thus reduce electric shock hazards.

The use of multiple-layer printed cables to re¬
duce the size of a computer and to decrease its
vunerability to shock and vibration is illustrated
in Figure 3. Each module, representing a memorv

or logic function, is an encapsulated printed-wiring
board with integral printed spring-contact fingers.
These packages are mounted on a printed cable-
stick which consists of four layers of printed wiring
and two printed connectors, one for test and the
other for power and signal supply. Each stick is a
plug-in unit which fits into a receptacle in the con¬
sole and can be tested as a functional unit.

The impact of printed circuits on automation in
the electronics industry is illustrated bv the in¬
creasing number of mechanical assembly systems
used to produce commercial and military electronic
equipment. There will continue to be a large num¬
ber of circuits which will not be economically
feasible to assemble automatically. The mech¬
anized assembling machines, however, will provide
industry with a substantial standby force of robot
assemblers, wiring hands and inspectors which can
be called upon to meet sudden demands for a
large amount of equipment. This would certainly
be true in the case of military emergency when
the defense services would require a tremendous
volume of tactical and strategic electronic systems.

It is quite evident now that printed circuits have
emerged from the laboratory' development stage
to become another in the series of new tools de¬
veloped to promote the advance of electronics.

N. Osircinx, a native of Phillipsburg, New [erse\, receiv ed his degree in Me¬
chanical Engineering from Rutgers University in 1951 after serving two and one-
half years in the Army. He joined Bell Laboratories that year as a member of the
Nike Missile S vs tom group and was enrolled in the Laboratories Communications
Development Training Program. In 1954 he transferred to the newlv formed
electromechanical development department, where he was in charge of a group
concerned with the study and development of printed-circuit processes and ap¬
plications. At present he is in charge of a group studying mechanical design
problems associated with radars and missile-borne equipment. He is a recipient
of the Lincoln Foundation Award and is a member of A.S.M.E. and Tan Beta Pi.

S. J. Stockflkth, a native of Bergen, Norway, came to the United States late
in 1924 after receiving his B.S. in E.E, in Germany. Upon completing a graduate
training course at the Westinghouse Corp., he joined the Manufacturing Develop¬
ment Department of the W estern Electric Company at Hawthorne, where he
developed multiple-coil winders and sealed-coil units, Mr. StockUeth transferred
to the Apparatus Development Department of Bell Laboratories in 1929, where
he worked on the development of dials, multi-contact and crossbar switches on
which he holds several patents. He was concerned with the mechanical design of
military equipment (hiring World War II, and after the war supervised a group
responsible for mechanical design of the Nike System radars. Since 1953 he has
been in charge of a subdepartment responsible for the mechanical design and
development of military radar antennas, missile equipment, printed circuits, and
the Whippanv Mechanical Laboratory.

Relay contacts in service sometimes erode much
faster than laboratory life tests indicate they
should. Often such erosion is due to “activation’*
— a subtle effect of organic vapors present in
the operating environment. Activation has been
studied for some years at Bell Laboratories, and
the phenomenon is now quite well understood.

If you ask a telephone engineer, “what is the
most important component in today’s switching
systems?”, he will probably reply, “relays.” The
“business end” of these dependable electromechani¬
cal devices is the contact end. Relay contacts, since
the advent of common-control switching systems,
have probably earned the right to be singled out
as the hardest workers in the telephone plant. A
modern relay, for example, may have to operate
more than 1,000 times in an hour.

In some cases, each contact operation may short¬
en the life of the relay because of “erosion” phe¬
nomena at work on the contacts. The amount of con¬
tact erosion — a direct measure of the amount by
which the life of the relav is shortened — mav varv

by a factor greater than 100 with differing en¬
vironmental conditions. Relay designers and re¬
search groups at Bell Laboratories have been aware
of and have studied the causes and effects of erosion

phenomena for many years. The effects of these
phenomena are obvious — degradation of telephone
service and increased relay maintenance. The
causes of erosion are more subtle, however, and
are only now becoming thoroughly understood.

The basic cause of erosion is electric arcs which
occur when relay contacts are opened or closed,
and a major factor influencing these arcs is a
phenomenon called “activation.” Activation is the
contamination of the metal surface of a contact
which gives rise to greater arcing (during either
the “making” or “breaking” of an electrical circuit)
than would occur at clean surfaces. This phenom¬
enon is produced by repeated operation of a pair
of current-carrying relay contacts in the presence
of organic vapor. Basically, it is these organic va¬
pors that cause increased arcing and increased con¬
tact erosion. The increase in arcing takes either of
two forms: arcs when there would have been none

without the vapor, and arcs that last longer in the
presence of vapor than they would in pure air.*

Organic vapors that produce activation come from
many sources. Some of these are the plasticizer in
the cellulose acetate of the relay coil winding, the
phenol fiber in the relay structure, and the paint
used on the walls of telephone central offices. Lab¬
oratory tests have shown that normally onlv noble-
metal surfaces become “active” and that activation
can be produced only by those organic compounds
which contain rings of carbon atoms with at least
one unsaturated bond between atoms in the ring.
Benzene and benzene derivatives are examples of
compounds with this molecular structure.

When a pair of palladium contacts is operated re¬
peatedly in the presence of such an organic vapor,
and the voltage across the contacts is displayed on
an oscilloscope, the trace would look, in the be¬
ginning, as if no vapor were present. This non-arc¬
ing condition, as it appears on the oscilloscope
screen, is shown in Figure 1(a). After continued op¬
eration, however, arcing can be observed. The arc¬
ing condition can be recognized by an irregular
trace similar to the one shown in Figure 1(b). Even
before any electrical effects are observable, how¬
ever, incipient activation can be detected micro¬
scopically by the presence of black, sooty material
on the contacts. This sooty substance is carbon, and
the amount necessary for activation is extremely
small — about 0.05 microgram.

Carbon is formed by the decomposition of or¬
ganic molecules adsorbed on the contact surfaces.
Arcs cause this decomposition, and the resulting
carbon enhances the severity of the arcing, so that
a vicious cycle of activation, arcs, carbon, increased
arcing, and so on, can easily get started. The amount

Fig. 1 Oscilloscope trace of (a) non-arcing con¬
tacts. and ( b) arcing at contacts after repeated op¬
eration in vapor. In both traces the circuit voltage
teas 35, indicated by the initial dots. The initial
horizontal line in (b) represents the potential
difference across the contacts during an arc lasting
for 2 microseconds. This teas folloued by an open-
circuit potential of 10 volts, lasting until final
closure (zero potential) at about 76 microseconds.

Fig . 2 — Plot of the rate of formation of carbon
on relay (ontacts in the presence of organic vapor.

of carbon formed by one arc corresponds initially
to about a single layer of organic molecules ad¬
sorbed on the portion of the contact covered by
the arc. The rate of carbon formation later increases
(Figure 2) to an amount corresponding to several
monolayers of molecules, presumablv because the
carbon already present increases the active surface
area of the relay contact.

In pure vapor, experiments have proved that the
amount of carbon formed per contact operation is
independent of the vapor pressure. When the va¬
por is simply part of the surrounding air, however,
the situation is complicated bv the presence of suffi¬
cient oxygen to burn some of the carbon already
formed, and by the impedance offered bv air to
diffusion of organic molecules to the electrode sur¬
faces. The rate of contact operation is a factor, too,
in carbon formation. If the contacts are operated
rapidly, less than a monolaver of activating mole¬
cules may be able to accumulate on the contact
surfaces in the brief time the contacts are separated.
These two factors — brief accumulation time and
carbon burning — establish a minimum pressure of
organic vapor below which the contacts of a relay
do not become active.

The presence of carbon on contact surfaces
changes both the character and intensity of the
arcs. Consequentlv, the character and magnitude of
the resulting erosion are also altered. We shall
consider first the character of erosion with and with¬
out carbon, and then the effect of the presence of
carbon on the amount of erosion.

Two distinct types of arcs occur between relay
contacts. The type of arcing which occurs in any
particular case is the dominant factor in determin¬
ing the character of the contact erosion. 0 \n “anode
arc” vaporizes metal predominantlv from the anode,

Fig. 3 Photomicrograph I approximately 715 di -
ameters i of marks made on cathode ( left) and
anode surfaces by a single arc of the anode type.

Here, the metal is vaporized hv the heating due to
electron bombardment, and a spatter of anode
metal is left on the cathode (Figure 3). The second
type, a “cathode arc”, vaporizes metal from mvriads
of individual spots on the cathode. In this case,
vaporization of the metal is caused bv resistance
heating, since almost the entire electron current
of the arc flows through one of these tiny spots,
vaporizing the metal with explosive suddenness.
Cathodes arcs damage the anode verv little, in
many cases producing much less damage than is
shown in Figure 4, except of course for the dis¬
persed metal spattered over from the cathode.

The type of arc — anode or cathode — is deter¬
mined bv the electrode separation at which the
arcs strike. At the beginning of an arc, a current
made up of field-emission electrons is drawn from
a single point on the cathode surface. If the elec¬
trode separation is small, a spot on the anode is
raised to the melting point bv electron bombard¬
ment before the current from the cathode becomes
large enough to melt the emitting point. The re¬
sulting arc is called an anode arc. If, on the other
hand, the separation is sufficientlv large, the emit¬
ting point is melted first because the field-emission
current spreads out considerablv before it reaches
the anode. In this case, the resulting arc is of the
cathode type. The critical electrode separation that
determines which sort of arc will occur is different
for different metals, increasing with the increasing
electrical conductivitv of the metal. For palladium,
the critical distance is about 0.5 micron, and for
silver, three to four microns.

Both anode and cathode arcs transfer metal from
one relav contact to the other when the contact
surfaces are clean. An anode arc transfers metal
from anode to cathode, and a cathode arc trans¬
fers metal from cathode 1 to anode. After many suc¬
cess ive arcs, a mound is built up on one electrode

and a pit is eroded into the other. This deposit-
erosion situation is entirely changed, however, by
the presence of surface carbon. In the case of palla¬
dium contacts, surfaces that have carbon on them,
so-called “active surfaces,” transfer little or no
metal, because the metal vaporized from one elec¬
trode is prevented from sticking to the other by
loose carbon on its surface. The eroded metal can
be recovered in the form of a loose, sooty powder
mixed with carbon.

Carbon on electrode surfaces gives rise to another
difference also. When carbon is present, each arc
occurs at a new place — where carbon has been
formed by preceding arcs, but not at the center
of the immediately preceding arc where the arc
has burned the carbon awav. This continual re¬
location of the arcs results in uniform erosion of
the electrode surfaces, with no formation of pits
or mounds. At silver contacts, less carbon is often
formed in the presence of organic vapors, and a
great deal of the metal eroded from one contact
mav stick to the other, even in the active condition.

The change from pit-and-mound erosion to ero¬
sion which is uniform over the contact surface is
not the only effect of the presence of carbon. A
still more important effect of activation is the pro¬
duction of many more cathode arcs than anode
arcs. Cathode arcs, as mentioned earlier, occur
when an arc strikes at a contact separation greater
than that giving rise to anode arcs. The presence
of surface carbon increases the tendency toward
arcing at wide separations, and this in turn results
in a tendency for the dominant loss of metal to be
from the cathode rather than from the anode.

Carbon on the electrode surfaces — resulting from
activation — increases the contact separation at
which arcing starts, because on an active surface

Fig. 4 -&A ppearance I 900 diameters ) of the cathode
(left) and of the anode after a single cathode arc.

an arc strikes when the electric field generates
electrostatic forces high enough to move the carbon
particles. At the same time, the motion of these
particles results in partial closing of the gap. In
many cases, the electric field at which an arc strikes
at carbonized surfaces is of the order of 0.5 x l() w
volts per centimeter, which at fifty volts is a separa¬
tion of one micron. This is considerably less than
the critical distance of three to four microns which
determines for silver electrodes whether an arc
will be of the anode or cathode tvpe.

Thus, activation does not, in most cases, alter the
type of arc at silver surfaces when the striking po¬
tential is fifty volts. But it mav alter the type of
arc at higher voltages as, for example, at separating
electrodes in an inductive circuit. For palladium
contacts, on the other hand, the critical distance
of 0.5 micron is so small that activation causes all
arcs to be of the cathode type. Between clean palla¬
dium surfaces, however, most arcs at fiftv volts are
anode arcs. At silver surfaces then, the loss of metal
is predominantly from the anode, whether the sur¬
faces are clean or carbonized. At palladium sur¬
faces (at 50 volts), loss is chieflv from the anode
when the surfaces are clean, but from the cathode
when they are active.

This situation is of course modified at high vol¬
tages. What will happen at am given voltage is
predictable, however, if both the critical distance
and the electrode separation at which an arc strikes
are known. For example, about 350 volts is the
minimum difference in potential at which the gases
in the air between the two electrodes “break down”
at atmospheric pressure. The distance at which vol¬
tages just above this value cause breakdown is about
fifteen microns. This distance is so great that for
voltages above 350, all arcs are cathode arcs for
silver as well as for palladium, whether the sur¬
faces are clean or active. These observations re¬

garding the character of erosion resulting from arcs
are presented in the table below.

To this point, we have been concerned with the
effect of organic vapors on the character of erosion
at contact surfaces. As brought out earlier, the
magnitude of the erosion is affected as well as the
character. In most cases, activation increases ero¬
sion by a large factor. This is due to two factors:
the greater separation at which arcs can strike be¬
tween active surfaces, and the lowering of the min¬
imum current which can sustain an arc between
such surfaces. The first of these effects — greater
contact separation for active arcs — has been dis¬
cussed above. This effect is also important in pro¬
longing the length of time of arcing as contacts are
pulled apart.

The second effect — the lowering of the “minimum
arc current” — is most readily understood bv consid¬
ering an arc of the cathode tvpe. For a cathode arc,
the minimum arc current is the lowest current which
will promptly explode a point on the cathode
through which the current flows. V carbon particle
on the cathode has relatively high electrical resis¬
tivity as well as poor thermal contact to the sup¬
porting metal. The lowest current which can ex¬
plode it, therefore, is much less than the minimum
current required to explode a spot on clean cathode
metal. Specifically, experiments have shown that
the minimum arc current for a clean metal surface
may be as high as one ampere but for a carbonized
surface it mav be as low as 0.03 ampere.

It is possibly this feature of activation — the low¬
ering of the minimum arc current — that makes con¬
tact activation most objectionable. At contacts with
a minimum arc current that is low, an arc can often
last for a much longer time than it would if the
minimum arc current were higher. This longer
arcing time results in greath increased erosion.

° At high vapor pressure. At low vapor pressures there ruay he an anode pit,
with much of the eroded metal sticking to the cathode in the form of a mound.

practice in telephone circuits to install a protective
network consisting of a capacitor in series with a
resistor across the contacts, or across the inductive
load. Such a circuit can be effective onlv when the
minimum arc current is higher than the circuit cur¬
rent. Thus, it turns out that active contacts in ' 2 -am-
pere circuits, fairly common in the telephone plant,
cannot be protected against arcing. Furthermore,
activation is damaging even in low-current circuits.
Here, intermittent arcing can occur due to the dis¬
charge of local capacitance. When contacts are ac¬
tive, the repeated discharge of local capacitance

may produce erosion that is almost as severe as the
erosion from a sustained arc in a circuit that is nor¬
mally considered as carrying a high current.

Although both the causes and effects of activation
are now well understood, the phenomenon never¬
theless sometimes presents problems in relay design.
Activation can be reduced both by using stable ma¬
terials which are not sources of organic vapors, and
by adequate ventilation. The cost and other con¬
sequences of any possible change are often an im¬
portant consideration, and what to do in any par¬
ticular case is not alwavs at once clear.

L. II. Gehmer, a native of Chicago, received the A.B. degree from Cornell
University in 191V, and the M.A. and Ph.D. degrees from Columbia University
in 1922 and 1927, respectively. In 1917, he joined the Engineering Department
of the Western Electric Company and has been at Western Electric and Bell
Laboratories since that time, except for a period from 1917 to 1919 when he
served in the U. S. Air Force. Mr. Germer’s work has been in various fields of
physical research including thermionics, electron diffraction, surface phenomena
and the phvsies of electrical contacts. He is the author of over seventv scientific
papers on these subjects.

J. L. Smith, a native of Morristown, N. }., joined the Laboratories in 1941 as
a messenger. After serving three years in the U. S. Navy, he returned to the Phvsi-
cal Research Department where he worked on problems concerned with relav
contact erosion. From 1946 to 1956 Mr. Smith attended the evening division of
the Newark College of Engineering, receiving the B.S. in E.E. degree. In 1956
he transferred to the Switching Development Department where he is currently
engaged in the design of switching networks using solid-state devices. Mr. Smith
is a member of Tan Beta Pi.

A major difficulty in the development of liigli-
lrequency transistors has heen the formation of
reliable electrical contacts between extremely
fine wires and minute areas of semiconductor
crystals. At Bell Laboratories, a promising solu¬
tion to this problem has heen found — a tech¬
nique known as tliemio-compression Ixmding.

For the past several years there has been a strong
trend toward miniaturized electronic devices. In
part, this trend is attributable to the great econo¬
mies possible with small, compact equipment. The
electronic telephone switching systems of the future,
for example, are expected to be so much less bulky
than present equipment that they should result in
considerable savings to the Bell System in floor
space and sizes of central offices.

There is, however, another important reason for
miniaturization of electronic circuits, stimulated in
large measure by the invention at Bell Laboratories
of the transistor. Because of its inherently small
size and lower power requirements, the transistor
permits other components in a circuit to be reduced
proportionately in size. Further, there has been
considerable emphasis on high-frequency opera¬
tion for greater bandwidth of communication sys¬
tems. Since the elements of electronic devices in
general become smaller at the higher frequencies,
this means that the already small transistor struc¬
ture has progressively become even smaller.

When structures are to be fabricated to virtual¬
ly microscopic dimensions, many complications ap¬
pear, not the least of which is the sheer mechanical

difficulty of working with tiny parts. In addition,
semiconductors are frequently sensitive to mechan¬
ical disturbances and to minute traces of unwanted
chemical contamination — a consideration that im¬
poses strict limitations on methods of fabrication.

In many such cases, an outstanding mechanical
difficulty is that of securing a bond between very
thin electrical conductors and the semiconductor.
The bond must be accurately positioned in a small
area; it must have the least possible effect on the
electrical characteristics of the semiconductor; and

Heat and pressure produce the bond with very little
contamination of the semiconductor material.

it must be mechanically strong and reliable. This
difficulty is overcome to a large degree by the
application of a new technique of joining solids
called thermo-compression bonding. The technique
is the result of fundamental research on the ad¬
hesion of solids* performed jointly bv O. L. Ander¬
son of the Research Department and the author.

Current practice of attaching leads to semicon¬
ductors involves alloying or soldering. These are

Fig. 2 — Tensile-strength curves for brittle fracture
(horizontal lines I and plastic yield (steep lines )
for germanium and silicon. Bonding region for ex¬
periments (shaded area l is well inside these limits .

objectionable because both involve a liquid phase,
which gives rise to problems of alloy depth control,
wetting and chemical contamination. The bond¬
ing process described here does not involve liquid
phase formation and hence avoids these problems.
As shown in functional schematic form in Figure 1,
it merely involves the application of heat and pres¬
sure to the members being bonded. When these
are applied for a few seconds, adhesion occurs. The
two main advantages of such a bond are its sim-
plicitv of formation and its freedom from chemical
contamination.

A 5000 to 10,000 psi pressure, 200 to 300°C tem¬
perature range, and a 5-second time interval are
appropriate conditions for formation of a bond
between a gold wire and a block of germanium.
The upper range of temperature and pressure are
used where the wire is hardened by cold working
or bv the addition of “doping” (impurity) metals
like aluminum or arsenic from the third and fifth
columns of the periodic table. Where metal-to-
metal bonds are to be made — for example in bond¬
ing leads to a transistor electrode — the time for
bonding can be reduced somewhat. Some cleaning

of the surface mav be necessary prior to the bond¬
ing operation. Gold wire is sometimes degreased
and annealed, but alloyed transistor emitter and
base electrodes, discussed later, are satisfactorily
clean as thev come from the alloying process.

The most important issue involved in application
of thermo-compression bonds to semiconductors is
the question of possible mechanical damage to the
semiconductor. Figure 2 relates temperature and
pressure of bonding to brittle fracture and plastic
stress of silicon and germanium. In this illustra¬
tion, the shaded area represents the region of suc¬
cessful bonding; it encompasses all the pressure and
temperature conditions used to date to bond gold,
silver, aluminum and various allovs of these ma¬
terials to silicon and germanium.

By noting the distance of the bonding region
from the curve for germanium, it is apparent that
sufficient margins exist for both temperature and
breaking strength. The curve for the onset of
plastic flow in the crystal is at least 10()°C from
the bonding region, and along the vertical axis,
breaking stress is seen to be at least double the
highest stress used for bonding. It is also apparent
in Figure 2 that silicon is even better in these re¬
spects. Actually, since no compression data for sili¬
con and germanium are available, tensile-strength
values are plotted in Figure 2, which means that the
safety factors are still higher. Several thermo-com¬
pression bond areas have been studied, and no in¬
crease in density of dislocations associated with

Fig . 3 — Extremely fine wire bonded by thermo¬
compression technique to electrodes of high-fre¬
quency transistor using germanium semiconductor.

Fig. 4 Gold lends thermo-compression bonded
to silicon in a power transistor. Bond passes 300
m I Hi am peres of continuous current.

press ion bonding was the attachment of lead wires
to evaporated and alloyed gold and aluminum
electrodes of d iff used-base transistors. Figure 3
shows an example of bonded leads on a high-fre¬
quency germanium transistor having verv closeh
spaced elements. The dark stripe is the aluminum
alloy emitter; it is about 0.006 inch by 0.001 inch.
The bright stripe is the alloyed gold base electrode.
The 0.0004-inch diameter gold lead wire is smaller
than can be made by direct drawing. It was formed
by first drawing down a silver-clad gold wire and
then dissolving away the silver. The resistance of
the bonded contact, after correction is made for
the lead resistance, is about 0.01 ohm. This is as
expected for a metallic contact without intervening
resistive skin. When the bonded lead is forcefullv
pulled away from the electrode, either the lead
wire breaks or a bit of germanium is extracted
with the wire, showing that the bond is stronger
than the weaker of the lead or germanium.

Figure 4 shows the bonded gold leads of a sili¬
con power transistor. The wire is 0.002 inch in
diameter, and the bond passes up to 300 milliam-
peres continuously without deterioration or fail¬
ure. All three electrodes shown here are of a gold-
silicon alloy. This photograph illustrates the fact
that the bond is also satisfactory for large power re¬
quirements. In this case, two base stripes are used
to reduce base resistance. In certain variations of
the development of this transistor, more than one
lead could be attached to the electrode. Such fea¬
tures and many others make thermo-compression
bonding attractive from the point of view of versa¬
tility of design.

The electrical characteristic of a metal-to-ger-
manium thermo-compression bond is of considerable
interest, both for potential application in device

technology and also for the investigation of a metal-
to-semiconductor interface. When carefully formed,
bonds of this sort give either rectifying or nonrecti¬
fying (ohmic) contacts in accordance with surface
doping produced bv the bonding wire.

Figure 5 illustrates the conditions under which
rectification is produced in a thermo-compression
bonded contact of an aluminum wire to a block
of n-type germanium. For the germanium under
this type of bond, curve A shows theoretical values
of spreading resistance—the resistance introduced
by the crowding of flow lines of electricity in the
germanium as they come to the confining area un¬
der the bond. Curve A is to be compared with
curve 13, yvhich represents actual data obtained
from a contact bonded in air. As can be seen, this
curve is intermediate to curve I). Data for curve
D were obtained after bond 13 was heated to a
temperature slightlv above the aluminum-germa¬
nium eutectic — the hnvest temperature that giv r es
a liquid phase when Ge and A1 are heated (425°C).
Curve C shows the effect of using a hvdrogen at¬
mosphere for bonding instead of air. In this case,
we have a bond that forms a rectifier that w ill
saturate. The difference between curves 13 and C
is accounted for by the contamination introduced
by the air ambient. Trace contamination on either
the wire or the germanium surface probably ac¬
counts for the difference between curves C and D
seen in Figure 5.

One distinct possibility for application of this
type of bond is the process illustrated by curve D.
At the expense of introducing a liquid-phase eutec¬
tic into the process, yve can form both an electrode
and a lead in one operation. A measure of control

Fig, 5 Theoretical “spreading resistance" (A)
compared to actual voltage-vs-current characteris¬
tic curves for bonds made by the various methods.

of alloy depth is obtainable in this case because
the liquid-phase eutectic forms at one or two de¬
grees above the eutectic temperature, and wetting
occurs over the bonded area. Another feature of
alloy depth control is the fact that the lead wire
can be of eutectic composition, so that it does not
require much germanium to go into solution to
form the liquid phase.

Thermo-compression bonding is thus seen to be
a significant advance in semiconductor technology.

By the application of heat and pressure, the bond
can be formed either with or without formation of
the liquid phase, as desired. The procedure may
be used to improve wetting and control of depth
in the alloying process. When a bond is made to a
semiconductor, the contact may be either ohmic
or rectifying, depending upon the doping of the
bonding wire and of the semiconductor. The tech¬
nique is presently being applied experimentally in
transistor fabrication at Bell Laboratories.

H. Christensen, a native of Manti, Utah, received the B.S. degree in physics
from Brigham Young University in 1930 and the M.A. degree, also in physics,
from Columbia University in 1935. He has been a member of the technical staff
of Bell Laboratories since 1930, when his first assignment was in the Submarine
Cable Research Department. In 1937 he began semiconductor material research
work, which he later used in the development of the thermistor bolometer. From
the beginning of World War II until 1950, Mr. Christensen worked on NDRC
and U. S. Navy contracts, and subsequently was engaged in investigation of
germanium material processing and surface phenomena. Since 1954 he has been
engaged in advanced development of diffused-base transistors. He is a member
of the American Phvsical Society and of the A.l.E.E.

The Western Electric Comp an v disclosed on
February 19 the receipt of a prime letter contract
from the U. S. Air Force for an important com¬
munications project in connection with a Ballistic
Missile Early Warning System, and said there
would be “substantial participation" by Bell Lab¬
oratories in the project. The text is as follows:

“A prime letter contract has been received from
the U. S. Air Fence authorizing the Western Elec¬
tric Company to proceed with the initial phases
of a communications project of major dimension
in connection with a Ballistic Missile Early Warning
System (BMEWS).

“Western Electric's responsibilities involve im¬
proving and augmenting communications in north¬
ern areas which will serve the new warning system
and which will be coordinated with other military
requirements. Work on the new project is already
underway.

“The Radio Corporation of America is prime con¬
tractor for the remote detection installations of
BMEWS as well as certain work at terminals in the
United States. Although RCA and Western Elec¬
tric have separate prime contracts, close coopera¬
tion will be required between the two companies on
those facilities concerned with the BMEWS project.

“At Western Electric, the work will be handled
by the Defense Projects Division where prior ex¬
perience with the DEW and White Alice systems
is expected to be of great value. There will be
substantial participation by the Laboratories in
technical areas, as well as the assistance of agencies
responsible for interconnecting commercial circuits.

“The contract covers responsibility for design,
installation and testing of new or augmented routes
outside of commercial areas and for overall com¬
munication s vs tern tests. Responsibilitv for con¬
struction of buildings and associated facilities has
not been announced. The project will require
standard Bell Svstem equipment as well as some
of new and special design. Western Electric will
manufacture the normallv supplied Bell System
items as well as certain of the new designs the
Companv’s plants may be especiallv qualified to
furnish. It is expected that a substantial portion will
be subcontracted to qualified manufacturers.

“The total personnel required is not known at
this time but it is expected that the present
staff on the DEW and White Alice projects will be
increased bv personnel from other Bell System
companies and Western Electric as the need for
particular skills develops."

Bell System earnings were $13 a share of Ameri¬
can Telephone and Telegraph Company stock in
1957, President Frederick R. Kappel said in the
company’s annual report, released February 18.

The earnings were based on the average of 63,-
811,000 shares outstanding—6,388,000 more than in
1956, when net income per average share equalled
$13.16. Bell System earnings on total capital were
6.7 per cent, compared with 6.8 per cent in 1956.

The Bell System spent more than $2.5 billion
in 1957 to enlarge and modernize telephone plant.
Most of the new capital obtained last year was
through the sale of bonds. These totaled just over
a billion dollars. The average interest cost, Mr.
Kappel pointed out, was nearly 4% per cent — the
highest in many years. Part of the money to ex¬
pand and improve telephone service in 1958 will
come from an issue of $718 million of debentures
convertible into stock. Share owners mav buy one
$100 debenture for each nine shares of stock held.

The A.T.&T. report, mailed to more than 1,600,-
000 share owners, cited many gains in service. It
stated, for example, that in 1957 the Bell System
added some 2,815,000 telephones, bringing the total
operated by the System to 52,250,000. Long dis¬
tance conversations rose more than 7 per cent
over 1956. Long distance service \\ as the fastest
ever. The average speed of connection was only
72 seconds. The Bell System changed a million
more telephones to dial service. Today 92 per cent
of Bell telephones are dial operated. Also, some
five million customers todav can use TDD” —
direct distance dialing — to as many as 30 million
other telephones from coast to coast. Another 10
million customers can dial nearby cities and towns.

The report also cited gains in undersea cable
service. Since the opening of the new telephone
cable between the Lb S. mainland and Hawaii last
October, calls to and from the island territory have
increased about 30 per cent. The first telephone

cable across the Atlantic, opened in 1956, is now
so heavily used that work has already begun on a
second cable which is expected to be ready in 1959.

Underhing all the progress, the A.T.&T. report
noted, are research at Bell Telephone Laboratories
and manufacture of equipment by Western Elec¬
tric. In addition, both organizations continue to
work on guided missile systems and other vital
defense projects.

Bell Telephone Laboratories, Mr. Kappel said, “is
one of the largest research organizations in indus¬
try. One reason is simph that there is so much
work to be done. Also, big size in itself is a distinct
asset. To make significant scientific discovery we

1C, L, Hawkins of the Chemical Research Depart¬
ment conduct in ft oxidation tests on polyethylene
to determine effectiveness of antioxidants.

C. IK Thurmond and Mrs. E. A. Wood discussing
structure of silicon as part of basic research into
properties of semiconductors .

need the best scientific minds. Those minds usually
want the stimulus of association with others of like
caliber, in a well-rounded scientific community that
has pre-eminent standing. This we have in Bell
Laboratories.

“There for many years the attack on communi¬
cation problems has begun with basic research —
the search for new understanding and knowledge
of nature. This has made possible long distance
service; the multiplication of talking paths over the
same physical conductors; the development of
radio relay systems; the creation of modern dial
switching systems; and many other developments.
In fact, the entire telephone network of today is
built on the knowledge which basic research has
supplied.

“The transistor, invented at Bell Laboratories
about ten years ago, is now finding many communi¬
cation uses: to route long distance calls automati¬
cally; to provide rural telephone circuits; to send
data at high speeds; to produce the ‘ringing signal’
in telephones; to amplify sound in other telephones
for people who have difficulty in hearing. . . . These
are examples. Also, development work continues
on the new electronic switching system in which
transistors play a vital part. This is a major under¬
taking. We are confident it will make possible many
new conveniences and improvements in service.

“Meanwhile basic research goes on. Bell System
scientists today are studying the effects of nuclear
radiation on crystals and plastics. They have found
new ways to join materials together—to bond them
so that thev may be used in ways previously im¬
possible. They are studying how to send huge
quantities of information over long distances
through hollow ‘waveguides/ Thev have demon¬
strated an entirely new microwave amplifier — a
small crystal in which, at a temperature near abso¬
lute zero, tbe spin of electrons in the atoms provides
the amplifying action. Such a device promises to
detect far weaker signals than could ever be de¬
tected before — even reflections from small objects
in outer space/'

Among the new developments now under way
at Bell Laboratories, Mr. Kappel said, is TASI —
short for “Time Assignment Speech Interpolation.”
TASI is expected to increase greatly tbe capacity
of telephone circuits such as those in the oceanic
cables.

“Today twin ocean cables (one for each direc¬
tion of talking) can carry 36 conversations at once,”
Mr. Kappel said. “What we look forward to is that
TASI may as much as double this capacity. This
it will do by taking advantage of tbe times when
people are listening or pausing. The voice chan¬
nels they leave temporarily unused will be auto¬
matically assigned to other talkers; and when a
listener starts to talk he will instantly have the
use of a channel which another person has left
idle."

The A.T.&T. president also commented on the
growing use of microwave radio: “In fact, use of
radio is sure to be more and more important in en¬
abling us to provide tbe best and most economical
service in years to come. We have therefore asked
the Federal Communications Commission to in¬
crease the number of microwave frequencies allo¬
cated to communication companies.

“The number of frequencies is limited, and a
policy assuring their orderly assignment to com¬
panies serving the general public will allow far
more efficient use of the radio spectrum than could
result from indiscriminate licensing for private
operation. Moreover, such a policy is essential to
permit expansion of the communication network
in ways that will best serve the nation’s defense.”

Because dependable switching apparatus is of basic importance to quality
of telephone serv ice. Bell Laboratories engineers conduct extensive reliability
studies. Their primary sources of data are actual performance records —
trouble tickets from central offices and other types of special information.

Modern electromagnetic switching offices con¬
tain a complex array of apparatus wired into cir¬
cuits to form a working unit. A single call estab¬
lished by this equipment may require the operation
of a thousand or more relays. Many thousands of
calls are handled daily by an office without inci¬
dent, but troubles do inevitably occur.

Troubles in central-office switching equipment
are, in general, apparatus or wiring troubles rather
than circuit difficulties. They include items such
as adjustment and contact troubles, defective parts,
and wiring defects. Whatever the cause, central-
office' troubles are of concern to Laboratories engi¬
neers because, fundamentally, good design must
take into consideration the effects of service use
and environment, and the reliability of the com¬
mercially-manufactured and installed product.

Knowledge of apparatus performance is obtained
from two sources: laboratory tests under simu¬
lated field conditions and actual field data. Of
these two, the laboratory tests are usually conducted
for specific reasons. They are valuable both because
they permit early evaluation of design and because
they can be so arranged that troubles occurring
during laboratory testing can be readily located.
For example, the new wire-spring relax, during

development and early production, was subjected
to manv laboratory tests of adjustment stability,
contact performance, and other characteristics.
These tests evaluated the effect on performance of
new features such as lowered contact pressure,
smaller contacts, gold-overlav contacts, and the
individual relay covers.

All the varied conditions of circuit usage, traffic
load, and environment met in the field, however,
cannot be duplicated in the laboratory. To provide
performance data under actual operating condi¬
tions, the Laboratories conducts frequent field
studies using detailed records of the troubles ex¬
perienced in central offices. These studies may be
limited to specific objectives or types of equipment,
or thev may be “system studies” in which complete
trouble records are obtained from a group of op¬
erating offices representing a particular system. An
advantage of systems studies is that they are not
confined to anv one portion of the switching office.
Thus thev may direct attention to unforeseen con¬
ditions in any element of the switching equipment.
Systems studies also provide a larger sample than
most laboratory tests and special studies.

Systems studies are based primarily on definitely
located troubles whose cause has been determined.

Fig. 1 — Data from the back of standard trouble
ticket are the major source of information for
the stitdies of telephone switching systems.

These are known as “found troubles.” In common-
control switching systems, found troubles are es¬
timated to be less than 10 per cent of total troubles
occurring in an average central office. A recent
study of No. 1 crossbar data indicated that, for
every trouble found, about twelve troubles are
“not found.” (A not-found trouble is one that can¬
not be specifically identified with a cause, either
because it cleared during tracing attempts, or be¬
cause tracing was unsuccessful or not attempted.)
Of the twelve not-found troubles, an attempt at
trouble location is made, on the average, in only
about three cases.

This low percentage of troubles traced and found
can be better understood by considering the nature

ot switching equipment and the trouble-location
procedures. Manv troubles are not service-affecting,
since the “second-trial” feature of crossbar systems
usualh' results in a valid connection. Both first- and
second-trial troubles do, however, automatically
leave a record of the progress of the call up to the
time the trouble occurred. Troubles are traced either
from these records or from other indications such
as alarms, stuck senders, routine test failures, or
reports from customers or traffic employees. Trou¬
ble indications include many cases of repeat or
multiple registrations from a single trouble. Also,
many of these indications are caused by conditions
in the outside plant or in connecting offices.

Economically, it is undesirable to use maintenance
time for tracing all indications of trouble, because
of the transient or intermittent nature of many of
them, and because the indications often cannot be
successfully analyzed. Troubles not traced or not
found probably include items such as transient
dirty contacts, partial loss or adjustment, or inter¬
mittent opens in windings or at wiring connections.
Found troubles, however, can be assumed to in¬
clude the more persistent troubles and those of an
urgent nature from the standpoint of service. Ac¬
tually, these are the only source of the specific in¬
formation required.

There are several considerations in planning sys¬
tems performance studies. First, results represen¬
tative of the system are sought. To this end, all
offices that qualify for study purposes are listed
in groups, based mainly on geographical location
and equal numbers of offices are selected at random
from each group for participation in the study. The
total number of offices selected is sufficient for a

statistically adequate sample. Offices chosen by
this method, known as “stratification,” represent a
variety of Operating Companies and areas, and sat¬
isfactorily provide a cross section of the svstem with
respect to environment, local maintenance prac¬
tices, traffic loads, and similar factors.

A second consideration in planning the studies
is the importance of obtaining, in addition to com¬
plete trouble records, certain supplementary in¬
formation that will permit proper interpretation
and presentation of the data. Requested from each
office is a count of each major type of equipment
and each type of relay. This provides a meaning¬
ful basis for prorating trouble data. In addition,
traffic data are obtained to indicate the call load
handled and to prorate trouble in terms of usage.
Other supplementary information concerns the en¬
vironment in which the switching equipment op¬
erates. It includes principally a record of any spe¬
cial activities, such as the Western Electric Com¬
pany installation work occurring during the study,
and information such as the type of ventilating
equipment used in the switchroom and whether or
not the humiditv is controlled.

A third consideration is the need to obtain accu¬
rate and complete data. Basically this depends on
cooperation of the field personnel involved and on
their understanding of the aims and requirements of
the study. Careful thought is given, therefore, to
the form in which the data is requested as well as
other details of initiating the study.

Found-trouble data are obtained from trouble
tickets which are the original records made by the
switchmen. Because trouble tickets are made out
for local use only 7 , they may be incomplete or even
misleading from the analyist’s viewpoint because
of varying use of terms b\ different personnel or
areas. To insure maximum accuracy and complete¬
ness of trouble reports and of other data, the Labo¬
ratories prepares a folder with special instruc¬
tions and definitions for the use of the personnel
reporting the data. The definitions apply primarily
to the back of the standard trouble ticket (Figure
1), which was designed mainly for study purposes
and provides more information than is generally
required for central office administration.

During the planning stage of the study, Labora¬
tories personnel visit some of the selected offices.
Discussions with Operating Company personnel on
the proposed forms and instructions and on the type
of data required have proved very helpful, and
have served to acquaint these people with the ob¬
jectives of the study.

In a typical systems study, five to ten thousand
trouble tickets may be received in the course of a
year. Full use of this information requires it to be
summarized in several wavs, and portions to be ex¬
tracted for detailed analysis. For instance, the analy¬
sis must show the troubles experienced in different
types of apparatus and circuits and the indications
that were effective in revealing these troubles. Also,
it may be necessary 7 to examine details, so that fac¬
tors such as the functional use of the apparatus at
fault may be considered in the analysis.

Through use of punched cards the data are
put into a form that will permit this flexibility in
summarizing and analyzing. The information ob¬
tained from each trouble ticket is translated into
codes which are, in turn, punched on the cards.
Each card represents one trouble. A coding sys¬
tem requiring a minimum of translation has been

developed for this purpose. Where possible it uses
standard apparatus codes or direct entry of such
information as the date, drawing number and con-
tact numbers. Figure 2 shows a page of coded in¬
formation for tickets received in a study 7 of No. 4A
toll offices. Arbitrary codes are used only for in¬
dicating the office, class of report, trouble type, and
to some extent, the apparatus tvpe. For apparatus
designated bv a number, as in the case of the 280-
tvpe relay, that number is entered directly. Let¬
tered types, however, are coded.

The tickets, in general, can be coded quickly and
easily In this ystem. Every study, however, in¬
cludes tickets with inconsistencies, obvious errors,
incomplete information, or statements that require
further clarification. Tickets, therefore, must be in¬
spected individually before they are coded, and
those raising questions that cannot be resolved are
sent to the study office either for more informa¬
tion or for explanations.

After the cards have been punched, business ma¬
chines sort and summarize them. The figures pro¬
vided by these summaries are used to compute
trouble rates — the number of troubles related to
the amount of equipment or number of calls han¬
dled. Table 1 shows a typical summary of trouble
rates for different types of relays, taken from a sys¬
tems study conducted in No. 5 crossbar offices.

To understand the significance of trouble rates,
many factors must be considered, such as the kinds
of functions performed, whether troubles occurred

Fig . 3 — Portion of chart of U and Y open-contact
troubles prepared to show the effect of installation
activity on trouble rates in three telephone offices .
THE AUTHOR_

in normal operation or were identified by routine
testing, and whether the troubles occurred in cir¬
cuits having a high or low frequency of operation.
Figure 3 is a chart prepared for study of the rela¬
tion sli ip between open-contact trouble rates and
the activities in progress in the offices. Such activity,
by adding to the dust in the air, may cause an in¬
crease in the number of open contacts.

Analysis of the data also includes statistical checks
on the consistency of the results from the individual
offices. A control chart for “defects per unit” is
used to spot instances where the data from a par¬
ticular office, because of unusual conditions, may
deviate too far from the average to be representa¬
tive of the system as a whole. Such data may be
excluded from the study results.

The final report presents summaries and includes
pertinent, detailed data for areas of particular in¬
terest. It also discusses probable factors affecting
malperformance and states conclusions. Engineers
sometimes request additional details on particular
types of trouble. Such data may come from sum¬
maries already made. If desired, the trouble tickets
involved can be identified from the punched cards
and drawn from the file for examination.

Significant results, at times unpredictable by
other methods, have been obtained from these
studies. In one case, results indicated the need for
further study of a particular type of relay, with re¬
sulting changes in design. Frequently, of course,
data affirm the success of design work by showing
consistently low rates of trouble. Study results have
contributed to the search for improved reliability
of telephone switching equipment, and provide a
background of reference data for estimating expect¬
ed trouble rates in new design and development
work. The nature of the data, combined with the
details available, makes these studies a valuable
source of information for many uses.

Mrs. Charlotte H. Hamilton, a native of New York City, joined the Develop¬
ment and Research Department of the A.T.&T. Company after receiving a B.S. de¬
gree from Teachers College, Columbn University, in 1924. She became a member
of the Laboratories in 1934. Her work has been concerned primarily with central-
office maintenance problems, and she lias conducted performance studies in toll
and local switching offices and in AM A centers. Her work during World War II
included the writing of instructions for the maintenance and testing of com¬
munications equipment for the armed services.

In automatic telephone switching systems, thousands of electrical connec¬
tions must he accurately established and frequently revised. A new circuit
has been developed for verifying the integrity of cross-connections in No. 5
crossbar offices — equipment which allows the frameman to perform his
functions faster and more conveniently than was formerly possible.

For the purpose of dialing calls or billing cus¬
tomers, a telephone is identified bv its number
appearing on the telephone instrument — the di¬
rectory number. In a No. 5 crossbar office the
same telephone line is also identified, for switching
purposes, as a location on a particular line-link
frame—the frame of crossbar switches that com¬
prise the first stage or last stage of automatic
switching in the office. This information consists
of a series of numbers specifying (1) the line-link
frame on which the telephone line appears, (2)
the horizontal group of crossbar switches, (3) the
vertical section of the crossbar switches called
“vertical group,” and (4) the “vertical file.” The
vertical file number refers to a particular line in
the vertical group, and thus completes the identi¬
fication of the telephone line.

This series is known as the “equipment number,”
and it has no fixed relationship to the directory
number. In fact, the arrangements are designed

Vo. 5 crossbar system; author , left , and R. J. De Dona of
the N. Y. Telephone Company setting up line tests .

for “full flexibility,” whereby any directory num¬
ber can be associated with any equipment number.
This permits telephone traffic to be distributed
evenly throughout the line-link frames to obtain a
uniform grade of service to all customers.

Flexibility of equipment number-versus-directory
number, however, requires the initial installation
of certain wiring on a “custom basis” for each tele¬
phone. Thereafter, occasional revision of this wir¬
ing is required to maintain a balance of traffic or
to process service orders. These wires, called cross-
connections, are so arranged that they may be
changed quite easily. Checking them for correct¬
ness is called line verification.

Prior to development of the new line-verification
equipment, verification tests were made by using
the master test control circuit, which is part of the
master test frame in a No. 5 crossbar office. In
many offices, there are periods when this frame
is almost continuously in use bv maintenance per¬
sonnel making routine operational tests on markers,
registers, senders, trunks or other units of equip¬
ment. Thus, verification tests of cross-connections
add to the work load of the maintenance center.
To relieve this congestion, and at the same time
to make the testing of cross-connections convenient
to the frameman who actually installs them, a sepa¬
rate line-verification facility has been developed.
This verification facility duplicates but does not
replace the verification features of the master test
frame in the office.

For the purposes of translation, cross-connections
are located in the number-group, line-link frame,
and AM A translator. The cross-connections of the
number group are used for translating the last four
digits of the directory number to its corresponding
equipment number, and also the ringing combina¬
tion and office-code group. The cross-connections of
the line-link frame are used for indicating the class
of service assigned to a vertical group and vertical
file. The AMA translator cross-connections are

Fig. 2 — Relay unit and control unit of the line-
verification equipment mounted on same frame.

lays are used. Figure 2 shows the relay unit
mounted in the upper part and the control unit
mounted with it in the lower part of the frame.

The line-verification circuit operates on the prin¬
ciple of “matching.” Information requiring transla¬
tion is sent to a marker for obtaining translation
from a number group or to a transverter for obtain¬
ing translation from an AMA translator. At the
same time, however, the known translation of this
input information is preset on switches in the veri¬
fication or test circuit. When the returned trans¬
lation is the same as that on the preset switches
in the test circuit — that is, when the two items
of information match — a “check” relay is operated
in the test circuit for that particular cross connec¬
tion. When check relays have operated for each
cross connection associated with the particular
line being tested, a verification match results.

For example, if the directory number 9753 is
to be verified, this number would be set up on
the “thousands,” “hundreds,” “tens” and “units”
switches of the verification circuit. Along with
this information, the corresponding equipment num¬
ber, which is obtained from office records or the
service order, is preset on switches of the verifica¬
tion-circuit panel. Such equipment numbers are
represented, for example, as “vg2” (vertical group

used for translating an equipment number to a
directory number, which is just the reverse of the
number-group translation.

Cross-connections are removed, added, or
changed to concur with disconnected, new, or re¬
located telephone service. Since an error in any
cross-connection will result in a wrong number,
it is important that these leads be installed cor¬
rectly, With this new verification circuit, cross-
connections may be checked immediately by the
frameman after he installs them.

The apparatus of the line-verification circuit is
mounted on two equipment units, one called a “con¬
trol” unit and the other a “relay” unit. The con¬
trol unit is a panel 12 inches high on which are
mounted switches, keys and lamps. This unit can
be mounted on a wall, the end of a distributing
frame, a desk, or a relay rack. Figure I shows the
mounting arrangement at the central office in
Tuckahoe, N. Y.

The relav unit is 32 inches high; it accommo¬
dates nine mounting plates and may be mounted
together with the control unit, or it may be mounted
remotely from the control panel. Wire-spring re¬

Fig. 3 — The " matching ” principle: simplified dia¬
gram shot vs verification of cross-connection in
number group of a Ao. 5 crossbar system.

A partial verification circuit is shown in Figure 3,
which illustrates a case wherein it is desired to
verify that a number-group cross-connection serv¬
ing the directory number 9753 is valid. The No. 5
crossbar marker takes the 9753, selects the proper
number group, and receives back the proper equip¬
ment number translation. Figure 3 shows circuitry
for only vertical group “2” and horizontal group
“3/' The vgn2 and hgn3 relays are merely two of
the many relays that operate in the marker as the
result of this translation. The verification circuit
has access, through the preset vg and iig switches
seen in the right part of Figure 3, to the correspond¬
ing vgn2 and hgn3 relay-operating paths in the
marker. Thus, the vg and hg relays (extreme right
in Figure 3) will operate and lock locally in the
verification circuit. To obtain an over-all verifica¬
tion check, all relays associated with cross-connec¬
tions must he operated in this manner in the veri
fi cat ion circuit, and ground is therebv closed to
operate the mlvm (marker line verification match)
relay. If one of the cross-connections — say hori¬
zontal group — is installed incorrectly, the hg relay-
operating path in the verification circuit would be
opened. The reason for this is that no other lead
would pass through the hg switch, since this switch
has been preset to the HG3 position. Thus, the iig
relay in the verification circuit would not operate,
which prevents the mlvm relay from operating.
In this ease, a lamp would light on the control
panel to indicate that the incorrectlv installed cross-
connection was the one associated with the hori¬
zontal-group information.

This verification circuit has access to either of
two marker groups. Bv virtue of the fact that the
marker is used for access to the number-group and
line-link frame cross-connections, this function is
called “marker line verification” or mlv. Similarly,
since the transverter is used for access to the trans¬
lator cross-connections, this function is called “trans¬
verter line verification” or tlv.

The new verification circuit fits into the No. 5
svstem as shown in Figure 4. With this block dia¬
gram and the flow numbers — the numbers on the
diagram indicating each step in the call — the
operational sequence of making a line-verification
test may be followed.

If the verification is to be of the mlv or marker
line verification type, the office-designation infor¬
mation and the number of the line to be verified
are preset on switches to be transmitted to the

marker for use by the number group. At the same
time, the correct line location, ringing combina¬
tion and class-of-service information for that line
are also preset on the control panel.

At the beginning of each test, a bid is made for
test preference in the master test frame connector
(1). This is necessary since this test circuit uses
the master test frame and test relays in the markers
and transverters in common with other test circuits.
If no other circuit has access to the master test
frame connector at this time, or when other circuits
which had access to the master test frame con¬
nector become idle, preference is given the line-
verification circuit. All other circuits which would
cause interference are locked out of the master test
frame connector.

The line-verification circuit connects, via the
master test frame connector, to a marker within the
particular group (2) and transfers the number and
office code group designation to the marker in
the same manner as an incoming register. The
marker connects to the proper number group (3)

Fig. 4 How the verification circuit is associated
with other circuits of the No. 5 crossbar system;
the numbers indicate steps in the test sequence .

Fig. 5 — Verification circuit conveniently located at right enables checking of the maze of cross-connec¬
tions in number group frames at left and AM A translator frames at the center of the photograph.

and transfers the number to it. The number is
translated into a line location and ringing combina¬
tion which the marker requires, and this informa¬
tion is returned to the marker (4). Using the line-
location information, the marker connects to the
line-link frame (5) and attempts to set up a con¬
nection in the normal manner.

The marker has recognized that this is a test call
and therefore does not complete the call to the line.
From the marker action, however, the cl ass-of-
service information is obtained from the line-link
frame by the marker (6). Since the verification
circuit has access to the leads over which the
marker receives the information from both the num¬
ber group and line link frame (7), a verification
lamp is lighted if the settings of the corresponding
switches agree with this information. If one or more
cross-connections are in error — thereby' causing
wrong information to be returned from the number
group or line-link frame — a lamp is lighted to indi-

The A\IA translator cross-connection check mav
be made independently of a marker line verifica¬
tion, or the verification circuit may be arranged to
recycle directly to the tlv stage immediately fol¬
lowing a succesful mlv verification. The line loca¬
tion and number of the line are preset on the same
switches used in mlv. The office index, which con¬
sists of a single digit in lieu of the first three digits
of the seven-digit directory number, is also set on a
rotary switch. In a manner similar to that of the
mlv test (1), the line-verification circuit connects
to a transverter and transfers to it the line location
(8). The transverter in turn transfers this line
location to the selected translator (9). The trans¬
lator translates the line location into an office index
and a four-digit directorv number, and then trans¬
fers these back to the transverter (10). If this in¬
formation matches the office index and directory
number previously preset on switches, an “ok

E. G. Crane, ]r, s a native of Trenton, N. ]., received a B.S. degree in Electrical
Engineering at Duke University in 1942. After a period with the General Electric
Co., he served during World War II as a Navv airborne electronics officer. Im¬
mediately thereafter he joined the N. f. Bell Telephone Company where he was
concerned with central office power plant equipment engineering. In 1951 he
transferred, on loan, to the Laboratories at Whippany, where he was involved
with the development of a military system for the Navy. In 1953 Mr. Crane
transferred to West Street where he became concerned with the development
of the No. 5 crossbar system, particularly in the application of wire-spring relay
circuits. The following year he became a permanent member of the Laboratories
and in recent years has been involved with circuit development of maintenance
facilities. He is a licensed professional engineer and received a M.S. degree from
Stevens Institute of Technology in 1949.

match” indication is given by a lighted lamp (11).
If a mismatch exists, which indicates that the instal¬
lation of a cross connection was incorrect, a lamp is
lighted to indicate the office index or directory
number that is involved in the mismatch.

Although the end result of tests with this equip¬
ment is primarily a visual display to indicate a
particular line verification, the circuit also has the
ability to leave behind a permanent record of a
verification if one is desired. This is produced on
the office trouble recorder and is obtained by oper¬
ating the record rec key at the control panel of the
verification equipment. When the rec key is oper¬
ated, upon each ok verification, a request is sent
to the marker or transverter for a record. A record
card is produced by the trouble recorder with all
the pertinent information — line number, equip¬
ment number, date and verification check. If de¬
sired, this information may be filed by the Oper¬
ating Company as a permanent record of the line

A field trial of this equipment has been success¬
fully conducted at the Tuckahoe office of the New
York Telephone Company. The control panel at
Tuckahoe is located at the end of the main dis¬
tributing frame, which is approximately midway
between the number group and AMA translator
frames. The relay panel is mounted on the miscel¬
laneous relay rack on another floor. Since this office
has all number groups, line-link frames and AMA
translators on one floor and the maintenance center
on another floor, and further, since there are two
marker groups, it provided an excellent oppor¬
tunity to observe the test circuit under conditions
where it is most needed. It proved to be very reli¬
able, and its performance was most satisfactory.
The trial also demonstrated the desirability for a
frameman to check his cross-connections immedi¬
ately after installation without interrupting other
testing at the maintenance center.

Patents Issued to Members of Hell Telephone
Laboratories During January

Bowman, B. M., and Rieke, J. \Y. - Polarizing Circuit for
Television Signals or the Like — 2,820,181.

Gorgas, J. \Y., Jacobitti E., Jaeger. R. J„ Jr., Morrison, C.
G., and Newsom, [. R. — Trouble Recording on Time-
Out Circuit for Automatic Telephone — 2,820,099.

Whelan. J. M. — Method of Purifying Silicon Tetrachloride
and Germanium Tetrachloride — 2.821,460.

In supplying radio channels for the AN/TRC-24
military telephone system, it was necessary to
design filters for use between the antenna and
transmitter and between the antenna and re¬
ceiver. The coaxial type of design resulted in a
small, efficient package, and it was found pos¬
sible to divide the entire 50 to 600 megacyles
range into only twenty-two sub-hands, with each
filter suitable for transmission and reception.

Some unknown radio engineer once observed
that the worth of a radio receiver is judged not by
what is received but by what is rejected. He was
probably a transmitter designer who was plagued
by complaints that his transmitter caused interfer¬
ence in receivers that he considered insufficiently
selective. The receiver designer similarly might
have said that the worth of a radio transmitter is
judged not bv what is transmitted but by what is
suppressed. Such epigrammatic statements, only
partially true and intended to impress and possibly
to confuse, merely emphasize the importance of the
“selectivity” of the device. This may be defined
as the ability of the receiver (or transmitter) to
receive (or transmit) the desired radio frequency
signal, while preventing the reception (or trans¬
mission) of unwanted frequencies.

Figure 1 is a block schematic showing the circuit
location of the filters. It is a characteristic of such
filters that the greater the tuning range, the greater
their complexity for a given amount of selectivity.
The tunable ranges of AN/TRC-24 are the “a"
band, 50-100 megacycles; “b” band, 100-225 me;
“c" band, 225-400 me; and ‘V band, 400-600 me.
Filters, tunable over each of these bands and fur¬
nishing the required selectivity, would be large,
mechanically intricate, and expensive. \ better
solution, and the one adopted, is to divide the
bands into smaller sub-bands and to design filters
for each sub-band. In this wav each filter tunes and
provides selectivity over a relatively narrow sub¬
band, which considerablv reduces mechanical com¬
plex] tv, size and cost.

The scheme has its unattractive aspect, however.
Since several filters are used to cover a main tuning
band, the selection of a filter is dependent upon
the frequency to which the transmitter or receiver
is tuned. The appropriate filter is plugged into the
radio-frequency head of the transmitter or receiver,
the others lying idle and creating a storage prob¬
lem. Since the transmitter and receiver frequencies
are not changed too often, howey'er, plug-in filters
do not impose a severe operational difficulty .

The “a,** “h,” and “c” bands are covered b\’ six
filters each, while the ‘V’ band uses four filters.
The filters for the transmitter must pass 100 watts
of rf power without undue dissipative loss or tem¬
perature rise. The receiver filters must pass only
transmitting^TV 1 /receiving

Fig . 1 —Location of tunable filters in t \ 7 /TRC-24
radio military telephone system .

extremely small amounts of poyver; however, they
are made identical to the transmitter filters to mini¬
mize the number of distinct designs. Actuallv, be¬
cause the transmitting and receiving frequencies
used at any given location are different, a single
set of filters is normally sufficient for a complete
installation. Plug-in dummy filters are supplied
yvith the radio equipment. When additional selec¬
tivity is not needed, the radio sets may be oper¬
ated without filters.

The filter circuit that appeared best able to sat¬
isfy the electrical requirements is shoyvn schemati¬
cally in Figure 3. In the formula shoyvn along

Fig. 2 Two views of typical filter; outer cylin¬
drical part of one coaxial section has been removed
to shoiv features of the internal structure.

yvith the diagram, R n is the impedance of the circuit
into yvdiich the filter yvorks, and f r is the midband
frequency of the filter's pass-band.

It should be realized that f r changes as the filter
is tuned over its oyvn sub-band. For design pur¬
poses, f r is chosen as the middle of the sub-band,
yvhich of course means that the design is theo¬
retically ideal only yvhen the filter is tuned to the
center frequency. But since the sub-bands are not
unduly yvide, the departure from the ideal is small,
even yvhen the filter is tuned to the edge of its
sub-band. An advantage of this type of circuit
is that by the use of coupling coils the designer may
choose the impedance level of the resonant cir¬
cuits for structural convenience, and then select

Fig . 3—Circuit for the tunable filter; coaxial-type
units are used for L 2 -C 2 -C, resonant circuits.

the coupling factor to yield the best over-all trans¬
mission performance.

After appropriate theoretical designs were
evolved, it was necessary to translate them into
physical elements. The frequenev range under
consideration, 50 to 600 megacycles, is not well
suited to the design of lumped-element filters —
that is, filters consisting of the conventional ca¬
pacitor and inductor components. At these fre¬
quencies, lumped elements involve troublesome
parasitic effects from connecting leads, and it is
difficult to construct them in convenient sizes pos¬
sessing adequately high “q” (small dissipation),
and high power-handling capability. The 50-600
me frequency range, however, is well-adapted to
the use of filters of the coaxial type. Elements of
this type are comparatively free from the afore¬
mentioned objectionable features of lumped ele¬
ments, and in addition are self-shielding and of
reasonable size. The filters, accordingly, were con¬
structed using these elements for the resonant cir¬
cuits designated L 2 ~C 2 -C ;} in Figure 3. The cou¬
pling inductances, L h were made in the form of a
single-turn loop, since extremely high “q” is not
required of them. The input and output coupling

Fig. 4 — Loss - frequency characteristic of filter
shoun in Figure 2; inset: expanded graph of region
of the characteristic curve near 152 me.

inductances to a cavitv are positioned to effect a
minimum coupling between them, which permits
the filters to realize the maximum out-of-band
discrimination.

Figure 2 shows a typical filter with one of the
outer coaxial conductors removed for display pur¬
poses. If this illustration is viewed in combination
with the schematic diagram, Figure 3, the com¬
ponent elements may be identified and the coaxial
type of construction is evident. For example, the
adjustable coaxial capacitors, C.* of Figures 3 and
5, tune the filter to the required frequency. This
particular filter has a useful tuning range of 142 to
163 megacycles per second. Figure 4 is an inser¬
tion-loss characteristic of the filter when tuned to
the frequency 152 megacycles per second. The
band loss is small, since the “q” of the coaxial ele¬
ments is high. The out-of-band discrimination, or
selectivity, more than satisfies the design require¬
ments for the system.

After achieving an appropriate electrical design,
it is necessary to design a suitable mechanical struc¬
ture. Such a structure must be accuratelv dimen-

sioned to provide accurate electrical properties and,
in addition, must he ruggedlv constructed to with¬
stand shock and vibration of transportation, and
severe weather conditions. Further, the structure
must he of a form that can he economically manu¬
factured in large quantities, and of a form that can
readily he plugged into the radio-frequency heads
of the transmitter and receiver. All of these features
are incorporated in the structure shown in Figure 2,
which is the basic structure used in all filters.

The dial mechanism is of a special design; it has
the axial motion required to varv the capacitance
of the coaxial capacitor used to tune the filter.
Simultaneouslv. the mechanism drives a dial plate
which is calibrated in terms of the various channels

When the filters are not in use they are housed in
convenient transit cases. These cases are similar
in design and construction to the ones used for
the transmitter and receiver. They provide protec¬
tion against adverse environmental conditions dur¬
ing transportation and storage.

Electrical and mechanical tests were applied to
representative models of these filters hv the U. S.
Signal Corps. The filters performed excellently,
and quantity production by the Western Electric
Company was undertaken. Although expressly
designed for the AN/TRC-24 radio set, the Signal
Corps has found them useful in a variety of other
applications.

M. I). Bhill, a native of New York Cite, joined Bell Telephone Laboratories
in 1930 after receiving the A.B. degree and the A.M. degree in Physics from
Columbia University. At the Laboratories he has been principally engaged in the
development of communication networks for Bell System use, except for a period
during World War II when he worked mainh on radio counter-measures devices.
After the war, Mr. Brill assumed responsibility for a group designing microwave
filters and networks for the TD-2. TH and Tf microwave radio-relay systems.
For the past year lie has been in charge of a group designing networks for
military projects.

K. M. Jensen, whose homo town is Hurlcv, South Dakota, received the B.A.
degree from the University of South Dakota in 1934 and the B.S. degree from
Purdue in 1937. He then joined the Laboratories and worked on the design of
audio equipment, and subsequently worked in the Quality Assurance Department.
In 1939 he transferred to the Transmission Networks Department where, during
World War II. he designed amplifiers, oscillators and filter circuits. Later, he was
engaged in the design of networks for carrier-telephone systems and tunable co¬
axial filters tor the AN/TRC-24 radio-relav system. Mr. Jensen is currently en¬
gaged in tlie development of microwave apparatus for the TJ and TH systems,
and of coaxial apparatus for a mobile radio system.

/\ D. Gam [left) and H . M. Gilroy examine polar -
o graph to ascertain elements in a metal solution.

The behavior of an electron tube in a circuit
depends to a large extent on the behavior of its
thermionic cathode. Thus, an accurate analysis of
the cathode metal aids in furthering the life expect¬
ancy of the tube. Long life is particularly advan¬
tageous for electron tubes that are used in such
inaccessable equipment as the recently installed
underseas cables.

The nickel used in cathode material contains
impurities that affect the ease and degree of activity
and the emission life. For example, certain elements
such as magnesium or aluminum are believed to
enhance the tube behavior, while other elements
such as silicon or manganese may have an adverse

Analysis of aluminum. The first increase in cur¬
rent indicates the reduction of an aluminum-dye
complex . The second increase indicates the reduc¬
tion of the uncomplexed dye . The closely spaced
peaks are caused by the formation and falling auay
of individual drops of mercury.

effect. It is important to know accuratelv the con¬
stituents of cathode metal so that cathode be¬
havior can be correlated with the amount of im¬
purities. With such information, manufacturers can
select proper alloy combinations to produce tubes
with longer life and higher thermionic activitv.

At Bell Laboratories a study has been made to
determine the most accurate method of analyzing
samples of manufactured cathodes. These sam¬
ples are analyzed after fabrication to determine
what impurities remain after chemical reactions
associated with the manufacturing process have
taken effect on the original nickel alloy. These reac¬
tions include processes such as absorption and seg¬
regation, and they also include the effects of a vola¬
tile substance.

The most rapid technique for this analysis em¬
ploys the spectrograph for the determination of the
presence of extraneous substances in nickel cathodes.
In this method, the entire cathode is converted into
an oxide and mixed with appropriate buffering
agents. The resulting powder mixture is packed
into a crater in a graphite rod. This composite is
brought into contact with a second graphite rod.
An applied dc potential across these two “elec¬
trodes,” as the interval between them is opened,
maintains an arc. Radiation from this arc is viewed
through a prism which scatters (spreads out and
separates) the light in a large number of character¬
istic wavelengths or colors. The scattered light is
intercepted either by a photographic plate or by
photocells. By studying the spectrum, the chemist
can detect the presence of elements from the num¬
ber and color of lines observed. He can also meas¬
ure the quantity of these elements from the intensity
of the color lines.

In searching for a more accurate technique, P. D.
Garn and H. M. Gilroy of the Laboratories Chem¬
ical Research Department have investigated an¬
other way of analyzing nickel cathodes — the
method of polarography. They have found this
method to be feasible, and thus have improved
the average accuracy from five per cent with spec-
trography to one or two per cent with polarography.
A further advantage of this method is that no stand¬
ards similar to the sample are required. Each im¬
purity is determined independently, and the pres¬
ence or absence of any other element has no ef¬
fect on an individual determination.

The polarograph uses the characteristics of cur-
rent-voltage curves to mark the existence and
amount of an element in a solution. To determine
the cathode constituents, the metal is dissolved in
solution. A series of precipitations, filtrations, evap¬
orations, electrolyses, and additions of compounds
separates the solution into workable sub-solutions
that are studied polarographically.

A pair of electrodes — a polarizable cathode and
non-polarizable anode — are immersed in the solu¬
tion to be studied. The electrodes are connected

to an external circuit, which includes a pen-re¬
cording apparatus. A voltage is applied and is
steadily increased.

At a particular voltage the current flow suddenly
increases rapidly. This “polarographic wave” is
due to the reduction (change in valence state), of
the ion at the cathode. Each element has a char¬
acteristic reduction potential and the voltage at
which the current suddenly increases can be used
to identify the ion. The current does not increase
indefinitely because the supply of ions in the im¬
mediate vicinity of the cathode is quickly removed.
The current is limited, therefore, by the rate of
diffusion of the ions to the cathode surface. The
rate of diffusion, and thus the current, is propor¬
tional to the concentration of the ion in the bulk
of the solution.

Determining the presence and amount of iron
and manganese in the nickel alloy represents a
novel analytical method. The addition of triethano¬
lamine to solutions containing these two ele¬
ments results in an improved constant current and,
in turn, an improved definition of the polarographic
wave that represents the ions.

The Western Electric Company’s total sales in
1957 were $2,480,614,000, an increase of 4.5 per
cent over 1956, according to the annual report to
stockholders, published February 21. Sales to Bell
Companies reached a high of $1,821,198,000, a
10.5 per cent increase over 1956 sales.

This is the largest volume of business ever han¬
dled by the Company in a single year, although
changes toward the end of the vear by the Bell
Companies in many of their construction programs
caused a leveling off in Western Electric produc¬
tion and service activities.

About one quarter of total sales, or $575,175,000,
was to the Government for materials and services
related mainly to national defense projects, among
them the Distant Early Warning Line, in the Arc¬
tic, which was completed in July; the White Alice
System, in Alaska; and production of the Nike
ground-to-air missile system.

Despite some downward revisions of the Com¬
pany’s production program in the final months of
the year, output of many types of telephone prod-

nets exceeded 1956 peaks. By the end of the year
6,668,000 telephone sets, 134,500 million conductor-
feet of exchange cable and enough dial central
office switching equipment to serve 3,822,000 lines
were shipped. Company installers worked on some
60,000 projects in 7,200 cities and towns through¬
out the United States, setting new records for in¬
stalling, testing and readying for the Bell telephone
companies’ use, switching and other equipment for
3,614,000 dial lines.

The Company made purchases directly from
about 33,000 companies, 90 per cent of them small
businesses. In addition, transportation services were
provided by 3,000 other firms. The total paid by
Western Electric in 1957 for materials, parts, sup¬
plies and transportation was $1,224,000,000.

In connection with development of the Compa¬
ny’s technological resources during 1957, the annual
report makes special note of the establishment of
the Graduate Engineering Training Program and
of the first steps toward establishing an engineer¬
ing research center at Hopewell Township, N. J.

At the request of the A.T.&T. Co., Bell Labora¬
tories has developed equipment for trials of a new
communications service. During February, the new
service—called “Dataphone”—was offered on a lim¬
ited basis in three Bell System areas: Illinois Bell.
Michigan Bell and the New York Company.

Dataphone, which could be one of the most sig¬
nificant business developments of our times, is a
high-speed transmission service for sending and
receiving data over regular telephone lines (sec
Record, April , 1957, and September , 1957), It can
send information over telephone facilities 10 times
faster than present methods—about 800 words a
minute.

Designed to send information to and from cus¬
tomers’ data-processing machines in various loca¬
tions, Dataphone service makes use of special de¬
vices — subsets — which can handle various types
of business-machine codes. They interpret and
transmit data read from punched cards, magnetic
and paper tapes and other media. Thev can also
transmit text. Subsets are manufactured bv Western
Electric.

Wherever there is a telephone there can be a
Dataphone subset — one of the advantages of the
new service. It can be plugged into a standard
electrical outlet to get its source of power.

Dataphone service has a promising future.
Eventually a person using the service will be able
to transmit data to anv point on the telephone net-

V. A. Vaughan, Jr., of the A.T.&T. Co. demonstrating Data -
phone subset equipment during press showing of the neic
systems for transmitting data over telephone lines.

work. It is also economical: a customer will pav
for the service much as he would for regular tele¬
phone service 1 . His main charge is based on how
much he uses it.

A businessman in New York can pick up a tele¬
phone associated with a Dataphone subset and
call another division of his company in Chicago,
He tells his associate in Chicago lie’s going to send
him some payroll data. Each presses a button on
his telephone, and information starts flowing over
the circuits from a business machine or from a
tape prepared in advance. His charge for sending
data is the same as for a regular long-distance tele¬
phone call.

If the businessman has several branches of his
company scattered across the land, he can trans¬
mit data at high speeds to one or to all of his
branches. Or people in his branch offices can take
information from their electronic counterparts and
send it back to headquarters.

Dataphone service can be provided at present
using two kinds of subsets — the Digital Subset
and the Recorded Carrier Subset. The Digital Sub¬
set converts electrical pulses of data received from
originating equipment (computers or tabulators,
for example) to audible tones for immediate trans¬
mission over telephone lines. At the receiving end,
the reverse function is performed. The equipment
takes the tones, reconverts them into electrical im¬
pulses and delivers the data to business machines.

The Recorded Carrier Subset through a tape re¬
corder permits storage of information received
from business machines for transmission at a later
time. Pulses are accepted from the machines at
relatively slow speeds and are recorded on mag¬
netic tape. Subsequently, the Recorded Carrier
Subset transmits the taped information to another
subset at the receiving end at a speed eight times
faster than the information was recorded. Thus,
24 minutes of information can bo compressed into
a three-minute call. At the receiving end, the pro¬
cedure is reversed — the information is “plaved
back” to business machines.

Also available are certain optional features not
requiring attendance bv operating personnel. For
instance, information can be stored on a Recorded
Carrier Subset throughout the day and transmitted
during the evening from and to a master station.
Thus, Dataphone makes it possible for machines

Left: a Digital Subset for immediate transmission
of data; and right: a Recorded Carrier Subset
which stores many types of data on magnetic tape .

A wide variety of business machines can be
adapted to Data phone equipment: card readers
and punches, various paper and magnetic tapes,
and teletypewriter equipment. As new commercial
machines are developed, thev can be designed to
be used with Dataphone equipment.

The Oliver E. Buckley Solid-State Phvsics Prize
for 1958 was presented during a recent joint meet¬
ing of the American Physical Society and the Ameri¬
can Association of Physics Teachers. The prize,
named for the former President of Bell Telephone
Laboratories, was awarded to Dr. Nicolaas Bloem-
bergen. Professor of Applied Phvsics at Harvard.

Bell Telephone Laboratories and the American
Physical Society established the prize, which con¬
sists of an award of $1,000 to a person adjudged
to have made a most important contribution to the
advancement of knowledge in solid-state physics
within the five years prior to the award. Dr.
Bloemhergen was the first to conceive a solid-state
MASER capable of continuous operation.

A new 7 open-shelf type of telephone “booth” has
been developed in the Station Apparatus Develop¬
ment Department at Bell Laboratories and is now
undergoing consumer tests at the Michigan and
Chesapeake and Potomac Telephone Companies.
The units, placed on trial through the A.T.&T. Co.
Customer Products Planning Division, may some
day provide supplements to regular booths in in¬
door locations, for example in department stores.

W estern Electric Co. made the shelf units at the
Queensboro, N. Y., Shop, and have turned out the
test models in three colors, red, tan and green.

{Below) D. H. King of the Apparatus Development
Department testing new“booth”at the Laboratories.

The Audio Engineering Society has announced
that Homer Dudley of the Laboratories has been
awarded a Letter of Commendation for his paper
“Fundamentals of Speech Synthesis. This paper
appeared in the Journal of the Audio Engineering
Society , Vol. 3, October, 1955.

in a letter accompanying the award, Mr. George
Horiuchi, Editor of the journal, cited Mr. Dudley
for his work in speech synthesis. “In particular,”
Mr. Horiuchi stated, “the excellent paper which
you contributed to our journal was the subject for
a great deal of favorable comment.” Mr. Dudley,
a member of the Visual and Acoustics Research
Department, is the inventor of the original Bell
Laboratories Vocoder machine for the study of
s peecli transmission.

This component has a constant-current feature
which makes it ideally suited for a current regu¬
lator in circuits where either the load or supplv
voltage vary over wide limits. It can also be used
as a current limiter or pnlse shaper. Its ac im¬
pedance is very high, making it useful as a coupling
choke or as an ac switch.

The device, closely related in principle to the
field-effect transistor (see Record, May, 1955), con¬
tains a single planar junction which is made by the
diffusion technique. Current passes parallel to this
junction through a constricted region called the
channel. As the voltage across the device is in¬
creased, current increases, and a depletion laver
builds up which eventually “reaches through** the
entire thickness of the channel. At this point, called
the “pinch-off” point, a further increase in voltage
does not produce any increase in current. Even¬
tually an avalanche breakdown occurs, as the volt¬
age is increased still further. Between pinch-off
and breakdown, the current is essentially constant.

At present these varistors are fabricated by cut¬
ting dice from a slice of germanium or silicon con¬
taining a single diffused junction. The dice are
heavily plated on all surfaces, and a circular trench
is then cut into the diffused laver to within about
0,1 mil of the junction (see Figure 1). This cutting

requires a high degree of precision, since the char¬
acteristics of the final device depend heavily on the
spacing between the bottom of the trench and the
junction. In exploratory work, the trench is first cut
with an ultrasonic tool and finished to the desired
depth by etching. Leads are then attached by
thermo-compression bonding or other means.

Characteristics of the device can be altered by
varying such parameters as channel depth, impurity
gradient, length and width of channel, and selec¬
tion of semiconductor material. Using silicon, units
have been fabricated with a regulated current of
one milliampere, pinch-off voltage of 10 volts and
breakdown of 150 volts.

Current can be held constant to within one per
cent over a voltage range of 20 to 120 volts. Ger¬
manium units have been made with a rating of 10
milliamperes, pinch-off of 10 volts and breakdown
of 25 volts. It appears feasible at present to produce
varistors which regulate current at any level be¬
tween 10 microamperes and 10 milliamperes, and
improvements in fabrication techniques should
make higher current levels possible.

For circuit applications, a parasitic shunt capaci¬
tance of the order of a few mmfd. is present and
must be taken into consideration. In the constant-
current region, the ratio of ac resistance to dc re¬
sistance is typically 100 and may run as high as
1000, making it ideal as a coupling device. It differs
from a conventional choke since impedance is con¬
stant over an appreciable frequency range.

Fig, 1 — Cross section of a field-effect varistor.
Circular trench is cut into the diffused layer.

Plans for construction of a direct submarine tele¬
phone cable system between the continental United
States and Puerto Rico have been announced
jointly by the Long Lines Department of American
Telephone and Telegraph Company and Interna¬
tional Telephone and Telegraph Corporation.

The announcement coincided with the filing of
construction applications with the Federal Com¬
munications Commission seeking authority to build
and operate the cable system.

The plans provide for work to start on the cable
system in 1958, with service scheduled for early
in I960. The cost, according to present estimates,
will he about $17 million and will be shared equally
by Long Lines and Radio Corporation of Puerto
Rico, a subsidiary of I. T. & T.

Telephone traffic between the mainland and
Puerto Rico has more than doubled during the last
five years. At the present time, telephone service
is handled bv radio.

Tlie March, 1958, issue of The Bell System
Technical Journal contains the following articles:

A etc Developments in Militanj Switching , bv A.
C\ Gilmore, P. R. Gray and W. S. Irvine.

Broadband Oscilloscope Tube , by D. J. Branga-
ccio, A. F. Dietrich and J. W. Sullivan.

Optimum Tolerance Assignment to Yiehl Mini¬
mum Manufacturing Cost , by David H. Evans.

The Measurement of Power Spectra from the
Point of View of Communications Engineering —
Part II, by R. B. Blackman and J. W. Tukey.

Following is a list of speakers, titles, and places of presentation
of recent talks giv en by members of the Laboratories.

American Institute ok Electrical Engineers Winter General Meeting New York On

Ball. W. C., Ground Measurement for Communication Cir¬
cuit Protection Planning.

Perrv, A. 13., Edson. J. O., and Flavin, M. A.. Synchronized
Clocks for Data Transmission.

Early, |. M., Xeic and Future Solid State Devices, Their
Properties and Apjilication,

Anderson, R. R., Dynamic Design and Test Problems of
Magnetic Tape Recorders , Am. Soc. of Mechanical Engi¬
neers, Johns Hopkins University, Baltimore, Md.

Bennett, \\ . R., Digital Transmission as a Random Process,
Electrical Engineering Department Seminar, M. I. T.,
Cambridge, Mass.

Berkerv, E. A., Potter Supply Design Factors, Ridgewood
Amateur Radio Club of \ T . J., Hohokns, N. |.

Biondi, F. J„ The Cleaning of Parts for Electronic Devices,
Am. Soc. for Testing Materials, Washington, D. C.

Ruppel, A. E., Methods of Evaluating The Transmission
Performance of the W Digital Data Signaling System.
Sliair, R. C, Lead-Acid Batteries in Telephone Service.
Smith, 13. II. A l-\Vatt Solar Power Plant .

Weboi, E. A., An b\l Digital Subset for Data Transmission
Over Telephone Lines.

Whitman, A. L.. Votaw, C. J., and Smith, C. W. (A.TAT.),
The HSR I Teletypewriter Selective-Calling System.

Myers, P. B.. james, 13. B., and johannesen, f. 13.. A Two-
Transistor Cate for Time-Division Switching.

Bozorth, R. \f.. Modern Magnetic Materials, Washington
Section, A.LETT, Washington, 13. C.

Brady, G. W., Structure in the Vitreous and Litfnid State,
Sigma Xi Societv. Corning Glass Works, Corning, N. Y.

Brattain, W. II., Development of Concepts in Semiconductor
Research , Cleveland Physics Society, Cleveland, Ohio.

Brattain, W. H., Surface Physics of Semiconductors, Journal
Seminar, Physics Dept., Case Institute of Technology,
Cleveland, Ohio.

Frisch, H. L., and Lloyd, S. P., One-Dimensional Impurity
Bands, Am. Physical Soc., N. Y. C.

Frisch, H. L., One-Dimensional Impurity Bands , Physics Col¬
loquium, Stevens Institute of Technology, Hoboken, N. J.

Geller, S., Garnets — Crystal Chemical and Magnetic Studies,
General and Physical Chemistry Seminar, Cornell Uni¬
versity, Ithaca, N. Y.

Gibbons, D. F., Role of Dislocations in Plasticity, Montreal
Chapter, A. S. M., McGill University, Montreal, Canada.

Grossman, A. J., Design of Networks, I.R.E. New York Sec¬
tion and A.I.E.E. Basic Science Division, N. Y. C.

Hagstrum, II. D., Electronic Transitions Between a Solid
and an Approaching Ion , Edison Laboratory, West Orange,
N. J., and Catalysis Club, Chicago, 111.

Ilersey, R. E., Sixty Million Telephones at Y our Fingertips,
Connecticut Valley Alumni Association, Phi Kappa Psi
Fraternity, Hartford, Conn.

Jensen, A. G., Efficient Use of Bandwidth, Philadelphia
A.I.E.E.-I.R.E, Lecture Series on Modern Communica¬
tion, Philadelphia, Pa.

King, J. C., Anelasticity of Synthetic Quartz at Low Tem¬
perature, Am, Physical Soc., N. Y. C.

Laudise, R. A., Hydrothermal Growth of Crystals, Am. Inst,
of Chemical Engineers, University of Virginia, Charlottes¬
ville, Va.

Liehr, A. D., The Coupling of Vibrational and Electronic
Motions in Degenerate Electronic States , University of
Michigan, Ann Arbor, Mich.; University of Colorado,
Boulder, Col.; and University of Chicago, Chicago, III.

MacKintosh, 1. M., New Developments in Transistor Engi¬
neering, Congregational Church, Scarsdale, N. Y.

MaeWilliams, W. H., The Use of Computers for Engineering
Development and Design, New York Section of the I.R.E.
Professional Group on Engineering Management, N. Y. C.

McMillan, B., A Theory of Communication , University of
Pennsylvania, Philadelphia, Pa.

Mertz, P., Information Theory Impact on Modern Comma nL
cations , Michigan Section A.I.E.E., Communications Tech¬
nical Committee, Michigan State University, East Lansing,
Mich.

Owens, C. D., A Look at Modern Magnetics for the Engi¬
neers, Merrimack Valley Subsection, A.I.E.E., Branch
Hall, Lawrence, Mass.

Pierce, J. R., Some Problems of Space Travel, Federal Tele¬
communications Laboratories, Nutlev, N. |.

Prince, E., Neutron Diffraction Problems on Magnetic
Oxides, U. S. Naval Research Laboratory, Washington,
D. C., and M. 1. T., Lexington, Mass.

Quate, C. F., Microwave Tubes—What is New?, I.R.E.
Subsection, White Plains, New York.

Rowen, J. H., Fundamentals of Ferromagnetism, Edison Re¬
search Laboratories, West Orange, N. J.

Slichtcr, W. P., Characteristics of Rubber-Like Materials,
New York Rubber Group, Course on Advanced Elastomer
Technology, N. Y. C.

Thatcher, W. II., NIKE — A Guided Missile System for
Anti-Aircraft Defense , College Club, Linden, N. J.

Vacca, G. N., Comparison of Accelerated and Natural Tests
for Ozone Resistance of Elastomers, Am. Soc. for Testing
Materials, Symposium on Ozone, St. Louis, Mo.

Winslow, F. PI., The Thermal Oxidation of Hydrocarbon
Polymers, Chemistry Seminar. Rutgers University, New
Brunswick, N. }.

Winslow, F. IP, New Protectants for Hydrocarbon Poly¬
mers, Pittsburgh Section, Am. Chemical Soc., Mellon In¬
stitute, Pittsburgh, Pa.

Wood, E. A., Opportunities for Women in Industrial Re¬
search, Douglass College, Rutgers University Career
Forum, New Brunswick, N. J.

Wooley, M. C., Components for Submarine Telephone Cable
Repeaters, Dayton Section I.R.E., Professional Group on
Components, Dayton, Ohio.

Following is a list of the authors, titles and places of publication
of recent papers published bv members of the Laboratories:

Eisinger, J., Electrical Properties of Nitrogen Adsorbed on
Tungsten, J. Chem. Phys., 28, pp. 165-166, Jan., 1958.

Ferrell, E. B., Control Charts for Log Normal Universe, 1958
Middle Atlantic Conference Transactions, pp. 137-142,
Feb. 28-March 1, 1958.

Fletcher, R. C., Physical Phenomena of the Solid State, Proc.
of the Symposium on the Role of Solid State Phenomena
in Electric Circuits, 7, pp. 41-62, 1957.

Law, J. T., The Interaction of Oxygen ivith Clean Silicon
Surfaces, J, Phvs. and Chemistry of Solids, 4, p. 91, 1958.

Mason, W. 1\, Ferroelectrics, Proc. of Symposium on the
Role of Solid State Phenomena in Electric Circuits, 7,
pp. 91-108, Feb. 27, 1958.

Mayzner, M. S., and Tresselt, M. E. (NYU), Shifts in Con-
notative Meaning of Words as a Function of Previous Re¬
strictive Experience, J. of Experimental Psychology, 55,
pp. 200-205, 1958.

McAfee, K. B., |r., Stress Enhanced Diffusion in Glass — I.
Glass Under Tension and Compression — II. Glass Under
Shear, J. Chem. Phys., 28, pp. 218-229.

McDavitt, M. B., 6000 Mega cycles/Sec. Radio Relay System
for Broad-Band, Long Haul Service in the Bell System ,
Communication and Electronics, 34, pp. 715-722, Jan.,
1958.

Waite, T. R., A General Theory of Bimolecular Reaction
Rates in Solids and Liquids, J. Chem. Phvs.. 28, pp. 103-
106, Jan., 1958.

Wernick, J. II., Geller, S., and Benson, K. E., X-Ray Powder
Data for Synthetic Proustite , Ag AsSn, Analytical Chemis¬
try, 30, p. 303, Feb., 1958,

Bell Laboratories Record 1958 04 1