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Edison, His Life and Inventions by Frank Lewis Dyer and Thomas Commerford Martin

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going after each other hammer and tongs, the arguments
TO HIM being carried on at the very top of one's
voice to enable him to hear, and FROM HIM being equally
loud in the excitement of the discussion, he has often
said: "I see now that my position was absolutely
rotten. "

Obviously, however, all of these personal characteristics
have nothing to do with Edison's position in the
world of affairs. They show him to be a plain, easy-
going, placid American, with no sense of self-importance,
and ready at all times to have his mind turned
into a lighter channel. In private life they show him
to be a good citizen, a good family man, absolutely
moral, temperate in all things, and of great charitableness
to all mankind. But what of his position in the
age in which he lives? Where does he rank in the
mountain range of great Americans?

It is believed that from the other chapters of this
book the reader can formulate his own answer to the


THE reader who has followed the foregoing narrative
may feel that inasmuch as it is intended to
be an historical document, an appropriate addendum
thereto would be a digest of all the inventions of
Edison. The desirability of such a digest is not to
be denied, but as there are some twenty-five hundred
or more inventions to be considered (including those
covered by caveats), the task of its preparation would
be stupendous. Besides, the resultant data would
extend this book into several additional volumes,
thereby rendering it of value chiefly to the technical
student, but taking it beyond the bounds of biography.

We should, however, deem our presentation of Mr.
Edison's work to be imperfectly executed if we neglected
to include an intelligible exposition of the broader
theoretical principles of his more important inventions. In
the following Appendix we have therefore endeavored
to present a few brief statements regarding Mr. Edison's
principal inventions, classified as to subject-
matter and explained in language as free from
technicalities as is possible. No attempt has been made
to conform with strictly scientific terminology, but,
for the benefit of the general reader, well-understood
conventional expressions, such as "flow of current,"
etc., have been employed. It should be borne in
mind that each of the following items has been treated
as a whole or class, generally speaking, and not as a
digest of all the individual patents relating to it.
Any one who is sufficiently interested can obtain copies
of any of the patents referred to for five cents each
by addressing the Commissioner of Patents, Washington,
D. C.



IN these modern days, when the Stock Ticker is in universal
use, one seldom, if ever, hears the name of Edison
coupled with the little instrument whose chatterings have
such tremendous import to the whole world. It is of much
interest, however, to remember the fact that it was by reason
of his notable work in connection with this device that
he first became known as an inventor. Indeed, it was
through the intrinsic merits of his improvements in stock
tickers that he made his real entree into commercial

The idea of the ticker did not originate with Edison, as
we have already seen in Chapter VII of the preceding narrative,
but at the time of his employment with the Western
Union, in Boston, in 1868, the crudities of the earlier forms
made an impression on his practical mind, and he got out
an improved instrument of his own, which he introduced in
Boston through the aid of a professional promoter. Edison,
then only twenty-one, had less business experience than the
promoter, through whose manipulation he soon lost his financial
interest in this early ticker enterprise. The narrative
tells of his coming to New York in 1869, and immediately
plunging into the business of gold and stock reporting. It
was at this period that his real work on stock printers
commenced, first individually, and later as a co-worker with
F. L. Pope. This inventive period extended over a number
of years, during which time he took out forty-six patents on
stock-printing instruments and devices, two of such patents
being issued to Edison and Pope as joint inventors. These
various inventions were mostly in the line of development of
the art as it progressed during those early years, but out
of it all came the Edison universal printer, which entered
into very extensive use, and which is still used throughout
the United States and in some foreign countries to a
considerable extent at this very day.

Edison's inventive work on stock printers has left its
mark upon the art as it exists at the present time. In his
earlier work he directed his attention to the employment of
a single-circuit system, in which only one wire was required,
the two operations of setting the type-wheels and of printing
being controlled by separate electromagnets which were
actuated through polarized relays, as occasion required, one
polarity energizing the electromagnet controlling the type-
wheels, and the opposite polarity energizing the electromagnet
controlling the printing. Later on, however, he
changed over to a two-wire circuit, such as shown in Fig. 2
of this article in connection with the universal stock printer.
In the earliest days of the stock printer, Edison realized the
vital commercial importance of having all instruments recording
precisely alike at the same moment, and it was he
who first devised (in 1869) the "unison stop," by means of
which all connected instruments could at any moment be
brought to zero from the central transmitting station, and
thus be made to work in correspondence with the central
instrument and with one another. He also originated the
idea of using only one inking-pad and shifting it from side to
side to ink the type-wheels. It was also in Edison's stock
printer that the principle of shifting type-wheels was first
employed. Hence it will be seen that, as in many other
arts, he made a lasting impression in this one by the intrinsic
merits of the improvements resulting from his work

We shall not attempt to digest the forty-six patents above
named, nor to follow Edison through the progressive steps
which led to the completion of his universal printer, but
shall simply present a sketch of the instrument itself, and
follow with a very brief and general explanation of its theory.
The Edison universal printer, as it virtually appears in
practice, is illustrated in Fig. 1 below, from which it will be
seen that the most prominent parts are the two type-wheels,
the inking-pad, and the paper tape feeding from the reel,
all appropriately placed in a substantial framework.

The electromagnets and other actuating
mechanism cannot be seen plainly
in this figure, but are produced
diagrammatically in Fig. 2, and somewhat
enlarged for convenience of explanation.

It will be seen that there are two electromagnets, one of which, TM, is known
as the "type-magnet," and the other, PM, as the "press-magnet,"
the former having to do with the operation of the type-
wheels, and the latter with the pressing of the
paper tape against them. As will be seen from the
diagram, the armature, A, of the type-magnet
has an extension arm, on the end of which is
an escapement engaging with a toothed wheel placed at the extremity of the shaft
carrying the type-wheels. This extension arm is pivoted
at B. Hence, as the armature is alternately attracted
when current passes around its electromagnet, and
drawn up by the spring on cessation of current, it moves
up and down, thus actuating the escapement and causing a
rotation of the toothed wheel in the direction of the arrow.
This, in turn, brings any desired letters or figures on the
type-wheels to a central point, where they may be impressed
upon the paper tape. One type-wheel carries letters, and
the other one figures. These two wheels are mounted rigidly
on a sleeve carried by the wheel-shaft. As it is desired
to print from only one type-wheel at a time, it becomes
necessary to shift them back and forth from time to time, in
order to bring the desired characters in line with the paper
tape. This is accomplished through the movements of a
three-arm rocking-lever attached to the wheel-sleeve at
the end of the shaft. This lever is actuated through the
agency of two small pins carried by an arm projecting from
the press-lever, PL. As the latter moves up and down the
pins play upon the under side of the lower arm of the rocking-
lever, thus canting it and pushing the type-wheels to the
right or left, as the case may be. The operation of shifting
the type-wheels will be given further on.

The press-lever is actuated by the press-magnet. From
the diagram it will be seen that the armature of the latter
has a long, pivoted extension arm, or platen, trough-like in
shape, in which the paper tape runs. It has already been
noted that the object of the press-lever is to press this tape
against that character of the type-wheel centrally located
above it at the moment. It will at once be perceived that
this action takes place when current flows through the
electromagnet and its armature is attracted downward, the
platen again dropping away from the type-wheel as the
armature is released upon cessation of current. The paper
"feed" is shown at the end of the press-lever, and consists
of a push "dog," or pawl, which operates to urge the paper
forward as the press-lever descends.

The worm-gear which appears in the diagram on the shaft,
near the toothed wheel, forms part of the unison stop above
referred to, but this device is not shown in full, in order to
avoid unnecessary complications of the drawing.

At the right-hand side of the diagram (Fig. 2) is shown a
portion of the transmitting apparatus at a central office.
Generally speaking, this consists of a motor-driven cylinder
having metallic pins placed at intervals, and arranged
spirally, around its periphery. These pins correspond in
number to the characters on the type-wheels. A keyboard
(not shown) is arranged above the cylinder, having keys
lettered and numbered corresponding to the letters and
figures on the type-wheels. Upon depressing any one of
these keys the motion of the cylinder is arrested when one
of its pins is caught and held by the depressed key. When
the key is released the cylinder continues in motion. Hence,
it is evident that the revolution of the cylinder may be
interrupted as often as desired by manipulation of the various
keys in transmitting the letters and figures which are to be
recorded by the printing instrument. The method of transmission
will presently appear.

In the sketch (Fig. 2) there will be seen, mounted upon
the cylinder shaft, two wheels made up of metallic segments
insulated from each other, and upon the hubs of these
wheels are two brushes which connect with the main battery.
Resting upon the periphery of these two segmental wheels
there are two brushes to which are connected the wires which
carry the battery current to the type-magnet and press-
magnet, respectively, as the brushes make circuit by coming
in contact with the metallic segments. It will be remembered
that upon the cylinder there are as many pins as there
are characters on the type-wheels of the ticker, and one of
the segmental wheels, W, has a like number of metallic
segments, while upon the other wheel, W', there are only
one-half that number. The wheel W controls the supply of
current to the press-magnet, and the wheel W' to the type-
magnet. The type-magnet advances the letter and figure
wheels one step when the magnet is energized, and a succeeding
step when the circuit is broken. Hence, the metallic
contact surfaces on wheel W' are, as stated, only half as
many as on the wheel W, which controls the press-magnet.

It should be borne in mind, however, that the contact
surfaces and insulated surfaces on wheel W' are together
equal in number to the characters on the type-wheels, but
the retractile spring of TM does half the work of operating
the escapement. On the other hand, the wheel W has the
full number of contact surfaces, because it must provide
for the operative closure of the press-magnet circuit whether
the brush B' is in engagement with a metallic segment or
an insulated segment of the wheel W'. As the cylinder
revolves, the wheels are carried around with its shaft and
current impulses flow through the wires to the magnets as
the brushes make contact with the metallic segments of
these wheels.

One example will be sufficient to convey to the reader
an idea of the operation of the apparatus. Assuming, for
instance, that it is desired to send out the letters AM to the
printer, let us suppose that the pin corresponding to the
letter A is at one end of the cylinder and near the upper part
of its periphery, and that the letter M is about the centre
of the cylinder and near the lower part of its periphery.
The operator at the keyboard would depress the letter A,
whereupon the cylinder would in its revolution bring the
first-named pin against the key. During the rotation of the
cylinder a current would pass through wheel W' and actuate
TM, drawing down the armature and operating the escapement,
which would bring the type-wheel to a point where
the letter A would be central as regards the paper tape
When the cylinder came to rest, current would flow through
the brush of wheel W to PM, and its armature would be
attracted, causing the platen to be lifted and thus bringing
the paper tape in contact with the type-wheel and printing
the letter A. The operator next sends the letter M by
depressing the appropriate key. On account of the position
of the corresponding pin, the cylinder would make nearly
half a revolution before bringing the pin to the key. During
this half revolution the segmental wheels have also been
turning, and the brushes have transmitted a number of current
impulses to TM, which have caused it to operate the
escapement a corresponding number of times, thus turning
the type-wheels around to the letter M. When the cylinder
stops, current once more goes to the press-magnet, and the
operation of lifting and printing is repeated. As a matter
of fact, current flows over both circuits as the cylinder is
rotated, but the press-magnet is purposely made to be
comparatively "sluggish" and the narrowness of the segments
on wheel W tends to diminish the flow of current in the press
circuit until the cylinder comes to rest, when the current
continuously flows over that circuit without interruption
and fully energizes the press-magnet. The shifting of the
type-wheels is brought about as follows: On the keyboard
of the transmitter there are two characters known as "dots"--
namely, the letter dot and the figure dot. If the operator
presses one of these dot keys, it is engaged by an appropriate
pin on the revolving cylinder. Meanwhile the type-wheels
are rotating, carrying with them the rocking-lever, and current
is pulsating over both circuits. When the type-wheels
have arrived at the proper point the rocking-lever has been
carried to a position where its lower arm is directly over one
of the pins on the arm extending from the platen of the
press-lever. The cylinder stops, and current operates the
sluggish press-magnet, causing its armature to be attracted,
thus lifting the platen and its projecting arm. As the arm
lifts upward, the pin moves along the under side of the
lower arm of the rocking-lever, thus causing it to cant and
shift the type-wheels to the right or left, as desired. The
principles of operation of this apparatus have been confined
to a very brief and general description, but it is believed
to be sufficient for the scope of this article.

NOTE.--The illustrations in this article are reproduced from American Telegra-
and Encyclopedia of the Telegraph, by William Maver, Jr., by permission of
Maver Publishing Company, New York.



EDISON'S work in stock printers and telegraphy had marked
him as a rising man in the electrical art of the period
but his invention of quadruplex telegraphy in 1874 was what
brought him very prominently before the notice of the public.
Duplex telegraphy, or the sending of two separate messages
in opposite directions at the same time over one line
was known and practiced previous to this time, but quadruplex
telegraphy, or the simultaneous sending of four
separate messages, two in each direction, over a single line
had not been successfully accomplished, although it had
been the subject of many an inventor's dream and the object
of anxious efforts for many long years.

In the early part of 1873, and for some time afterward,
the system invented by Joseph Stearns was the duplex in
practical use. In April of that year, however, Edison took
up the study of the subject and filed two applications for
patents. One of these applications[23] embraced an invention
by which two messages could be sent not only duplex,
or in opposite directions as above explained, but could also
be sent "diplex"--that is to say, in one direction, simultaneously,
as separate and distinct messages, over the one line.
Thus there was introduced a new feature into the art of
multiplex telegraphy, for, whereas duplexing (accomplished
by varying the strength of the current) permitted messages
to be sent simultaneously from opposite stations, diplexing
(achieved by also varying the direction of the current) permitted
the simultaneous transmission of two messages from
the same station and their separate reception at the distant

[23] Afterward issued as Patent No. 162,633, April 27, 1875.

The quadruplex was the tempting goal toward which Edison
now constantly turned, and after more than a year's strenuous
work he filed a number of applications for patents in the
late summer of 1874. Among them was one which was issued
some years afterward as Patent No. 480,567, covering
his well-known quadruplex. He had improved his own
diplex, combined it with the Stearns duplex and thereby
produced a system by means of which four messages could
be sent over a single line at the same time, two in each

As the reader will probably be interested to learn something
of the theoretical principles of this fascinating invention,
we shall endeavor to offer a brief and condensed explanation
thereof with as little technicality as the subject
will permit. This explanation will necessarily be of somewhat
elementary character for the benefit of the lay reader,
whose indulgence is asked for an occasional reiteration
introduced for the sake of clearness of comprehension. While
the apparatus and the circuits are seemingly very intricate,
the principles are really quite simple, and the difficulty of
comprehension is more apparent than real if the underlying
phenomena are studied attentively.

At the root of all systems of telegraphy, including multiplex
systems, there lies the single basic principle upon which
their performance depends--namely, the obtaining of a
slight mechanical movement at the more or less distant end
of a telegraph line. This is accomplished through the
utilization of the phenomena of electromagnetism. These
phenomena are easy of comprehension and demonstration.
If a rod of soft iron be wound around with a number of turns
of insulated wire, and a current of electricity be sent through
the wire, the rod will be instantly magnetized and will remain
a magnet as long as the current flows; but when the
current is cut off the magnetic effect instantly ceases. This
device is known as an electromagnet, and the charging and
discharging of such a magnet may, of course, be repeated
indefinitely. Inasmuch as a magnet has the power of attracting
to itself pieces of iron or steel, the basic importance
of an electromagnet in telegraphy will be at once apparent
when we consider the sounder, whose clicks are familiar to
every ear. This instrument consists essentially of an electro-
magnet of horseshoe form with its two poles close together,
and with its armature, a bar of iron, maintained in close
proximity to the poles, but kept normally in a retracted position
by a spring. When the distant operator presses down
his key the circuit is closed and a current passes along the
line and through the (generally two) coils of the electromagnet,
thus magnetizing the iron core. Its attractive power
draws the armature toward the poles. When the operator
releases the pressure on his key the circuit is broken, current
does not flow, the magnetic effect ceases, and the armature
is drawn back by its spring. These movements give rise
to the clicking sounds which represent the dots and dashes
of the Morse or other alphabet as transmitted by the operator.
Similar movements, produced in like manner, are availed
of in another instrument known as the relay, whose office
is to act practically as an automatic transmitter key, repeating
the messages received in its coils, and sending them
on to the next section of the line, equipped with its own
battery; or, when the message is intended for its own station,
sending the message to an adjacent sounder included
in a local battery circuit. With a simple circuit, therefore,
between two stations and where an intermediate battery is
not necessary, a relay is not used.

Passing on to the consideration of another phase of the
phenomena of electromagnetism, the reader's attention is
called to Fig. 1, in which will be seen on the left a simple
form of electromagnet consisting of a bar of soft iron wound
around with insulated wire, through which a current is flowing
from a battery. The arrows indicate the direction of

All magnets have two poles, north and south. A permanent
magnet (made of steel, which, as distinguished from soft
iron, retains its magnetism for long periods) is so called
because it is permanently magnetized and its polarity remains
fixed. In an electromagnet the magnetism exists
only as long as current is flowing through the wire, and the
polarity of the soft-iron bar is determined by the DIRECTION
of flow of current around it for the time being. If the direction
is reversed, the polarity will also be reversed. Assuming,
for instance, the bar to be end-on toward the observer,
that end will be a south pole if the current is flowing
from left to right, clockwise, around the bar; or a north
pole if flowing in the other direction, as illustrated at the
right of the figure. It is immaterial which way the wire is
wound around the bar, the determining factor of polarity
being the DIRECTION of the current. It will be clear, therefore,
that if two EQUAL currents be passed around a bar in opposite
directions (Fig. 3) they will tend to produce exactly opposite
polarities and thus neutralize each other. Hence, the bar
would remain non-magnetic.

As the path to the quadruplex passes through the duplex,
let us consider the Stearns system, after noting one other
principle--namely, that if more than one path is presented
in which an electric current may complete its circuit, it
divides in proportion to the resistance of each path. Hence,
if we connect one pole of a battery with the earth, and from
the other pole run to the earth two wires of equal resistance
as illustrated in Fig. 2, equal currents will traverse
the wires.

The above principles were employed in the Stearns differential
duplex system in the following manner: Referring to
Fig. 3, suppose a wire, A, is led from a battery around a bar
of soft iron from left to right, and another wire of equal
resistance and equal number of turns, B, around from right
to left. The flow of current will cause two equal opposing
actions to be set up in the bar; one will exactly offset the
other, and no magnetic effect will be produced. A relay
thus wound is known as a differential relay--more generally
called a neutral relay.

The non-technical reader may wonder what use can possibly
be made of an apparently non-operative piece of appara-
tus. It must be borne in mind, however, in considering a
duplex system, that a differential relay is used AT EACH END
of the line and forms part of the circuit; and that while each
relay must be absolutely unresponsive to the signals SENT
OUT FROM ITS HOME OFFICE, it must respond to signals transmitted
by a DISTANT OFFICE. Hence, the next figure (4), with
its accompanying explanation, will probably make the
matter clear. If another battery, D, be introduced at the
distant end of the wire A the differential or neutral relay
becomes actively operative as follows: Battery C supplies
wires A and B with an equal current, but battery D doubles
the strength of the current traversing wire A. This is sufficient
to not only neutralize the magnetism which the cur-
rent in wire B would tend to set up, but also--by reason of
the excess of current in wire A--to make the bar a magnet
whose polarity would be determined by the direction of the
flow of current around it.

In the arrangement shown in Fig. 4 the batteries are so
connected that current flow is in the same direction, thus
doubling the amount of current flowing through wire A.
But suppose the batteries were so connected that the current
from each set flowed in an opposite direction? The result
would be that these currents would oppose and neutralize
each other, and, therefore, none would flow in wire A.
Inasmuch, however, as there is nothing to hinder, current
would flow from battery C through wire B, and the bar
would therefore be magnetized. Hence, assuming that the
relay is to be actuated from the distant end, D, it is in a
sense immaterial whether the batteries connected with wire
A assist or oppose each other, as, in either case, the bar would
be magnetized only through the operation of the distant key.

A slight elaboration of Fig. 4 will further illustrate the
principle of the differential duplex. In Fig. 5 are two stations,
A the home end, and B the distant station to which
a message is to be sent. The relay at each end has two coils,
1 and 2, No. 1 in each case being known as the "main-line
coil" and 2 as the "artificial-line coil." The latter, in each
case, has in its circuit a resistance, R, to compensate for the
resistance of the main line, so that there shall be no inequalities
in the circuits. The artificial line, as well as that
to which the two coils are joined, are connected to earth.
There is a battery, C, and a key, K. When the key is depressed,
current flows through the relay coils at A, but no
magnetism is produced, as they oppose each other. The
current, however, flows out through the main-line coil over
the line and through the main-line coil 1 at B, completing
its circuit to earth and magnetizing the bar of the relay,
thus causing its armature to be attracted. On releasing
the key the circuit is broken and magnetism instantly ceases.

It will be evident, therefore, that the operator at A may
cause the relay at B to act without affecting his own relay.
Similar effects would be produced from B to A if the battery
and key were placed at the B end.

If, therefore, like instruments are placed at each end of
the line, as in Fig. 6, we have a differential duplex arrangement
by means of which two operators may actuate relays
at the ends distant from them, without causing the operation
of the relays at their home ends. In practice this is
done by means of a special instrument known as a continuity
preserving transmitter, or, usually, as a transmitter.
This consists of an electromagnet, T, operated by a key, K,
and separate battery. The armature lever, L, is long,
pivoted in the centre, and is bent over at the end. At a
point a little beyond its centre is a small piece of insulating
material to which is screwed a strip of spring metal,
S. Conveniently placed with reference to the end of the
lever is a bent metallic piece, P, having a contact screw in
its upper horizontal arm, and attached to the lower end of
this bent piece is a post, or standard, to which the main
battery is electrically connected. The relay coils are connected
by wire to the spring piece, S, and the armature lever
is connected to earth. If the key is depressed, the armature
is attracted and its bent end is moved upward, depressing
the spring which makes contact with the upper screw,
which places the battery to the line, and simultaneously
breaks the ground connection between the spring and the
upturned end of the lever, as shown at the left. When the
key is released the battery is again connected to earth.
The compensating resistances and condensers necessary for
a duplex arrangement are shown in the diagram.

In Fig. 6 one transmitter is shown as closed, at A, while
the other one is open. From our previous illustrations and
explanations it will be readily seen that, with the transmitter
closed at station A, current flows via post P, through
S, and to both relay coils at A, thence over the main line to
main-line coil at B, and down to earth through S and the
armature lever with its grounded wire. The relay at A
would be unresponsive, but the core of the relay at B would
be magnetized and its armature respond to signals from A.
In like manner, if the transmitter at B be closed, current
would flow through similar parts and thus cause the relay
at A to respond. If both transmitters be closed simultaneously,
both batteries will be placed to the line, which would
practically result in doubling the current in each of the
main-line coils, in consequence of which both relays are
energized and their armatures attracted through the operation
of the keys at the distant ends. Hence, two messages
can be sent in opposite directions over the same line simultaneously.

The reader will undoubtedly see quite clearly from the
above system, which rests upon varying the STRENGTH of the
current, that two messages could not be sent in the same
direction over the one line at the same time. To accomplish
this object Edison introduced another and distinct
feature--namely, the using of the same current, but ALSO
varying its DIRECTION of flow; that is to say, alternately
reversing the POLARITY of the batteries as applied to the line
and thus producing corresponding changes in the polarity
of another specially constructed type of relay, called a
polarized relay. To afford the reader a clear conception of
such a relay we would refer again to Fig. 1 and its explanation,
from which it appears that the polarity of a soft-iron bar
is determined not by the strength of the current flowing
around it but by the direction thereof.

With this idea clearly in mind, the theory of the polarized
relay, generally called "polar" relay, as presented in the
diagram (Fig. 7), will be readily understood.

A is a bar of soft iron, bent as shown, and wound around
with insulated copper wire, the ends of which are connected
with a battery, B, thus forming an electromagnet. An
essential part of this relay consists of a swinging PERMANENT
magnet, C, whose polarity remains fixed, that end between
the terminals of the electromagnet being a north pole.
Inasmuch as unlike poles of magnets are attracted to each
other and like poles repelled, it follows that this north pole
will be repelled by the north pole of the electromagnet, but
will swing over and be attracted by its south pole. If the
direction of flow of current be reversed, by reversing the
battery, the electromagnetic polarity also reverses and the
end of the permanent magnet swings over to the other side.
This is shown in the two figures of Fig. 7. This device being
a relay, its purpose is to repeat transmitted signals into a
local circuit, as before explained. For this purpose there are
provided at D and E a contact and a back stop, the former
of which is opened and closed by the swinging permanent
magnet, thus opening and closing the local circuit.

Manifestly there must be provided some convenient way
for rapidly transposing the direction of the current flow if
such a device as the polar relay is to be used for the reception
of telegraph messages, and this is accomplished by means
of an instrument called a pole-changer, which consists
essentially of a movable contact piece connected permanently
to the earth, or grounded, and arranged to connect one or
the other pole of a battery to the line and simultaneously
ground the other pole. This action of the pole-changer is
effected by movements of the armature of an electromagnet
through the manipulation of an ordinary telegraph key by
an operator at the home station, as in the operation of the
"transmitter," above referred to.

By a combination of the neutral relay and the polar relay
two operators, by manipulating two telegraph keys in the
ordinary way, can simultaneously send two messages over
one line in the SAME direction with the SAME current, one
operator varying its strength and the other operator varying
its polarity or direction of flow. This principle was covered
by Edison's Patent No. 162,633, and was known as
the "diplex" system, although, in the patent referred to,
Edison showed and claimed the adaptation of the principle
to duplex telegraphy. Indeed, as a matter of fact, it was
found that by winding the polar relay differentially and
arranging the circuits and collateral appliances appropriately,
the polar duplex system was more highly efficient than
the neutral system, and it is extensively used to the present

Thus far we have referred to two systems, one the neutral
or differential duplex, and the other the combination of the
neutral and polar relays, making a diplex system. By one
of these two systems a single wire could be used for sending
two messages in opposite directions, and by the other in
the same direction or in opposite directions. Edison followed
up his work on the diplex and combined the two
systems into the quadruplex, by means of which FOUR messages
could be sent and received simultaneously over the
one wire, two in each direction, thus employing eight
operators--four at each end--two sending and two receiving.
The general principles of quadruplex telegraphy are
based upon the phenomena which we have briefly outlined
in connection with the neutral relay and the polar relay.
The equipment of such a system at each end of the line consists
of these two instruments, together with the special
form of transmitter and the pole-changer and their keys for
actuating the neutral and polar relays at the other, or distant,
end. Besides these there are the compensating resistances
and condensers. All of these will be seen in the
diagram (Fig. 8). It will be understood, of course, that the
polar relay, as used in the quadruplex system, is wound
differentially, and therefore its operation is somewhat similar
in principle to that of the differentially wound neutral relay,
in that it does not respond to the operation of the key at the
home office, but only operates in response to the movements
of the distant key.

Our explanation has merely aimed to show the underlying
phenomena and principles in broad outline without entering
into more detail than was deemed absolutely necessary. It
should be stated, however, that between the outline and the
filling in of the details there was an enormous amount of
hard work, study, patient plodding, and endless experiments
before Edison finally perfected his quadruplex system
in the year 1874.

If it were attempted to offer here a detailed explanation
of the varied and numerous operations of the quadruplex,
this article would assume the proportions of a treatise. An
idea of their complexity may be gathered from the following,
which is quoted from American Telegraphy and Encyclopedia
of the Telegraph, by William Maver, Jr.:

"It may well be doubted whether in the whole range of
applied electricity there occur such beautiful combinations,
so quickly made, broken up, and others reformed, as in the
operation of the Edison quadruplex. For example, it is
quite demonstrable that during the making of a simple dash
of the Morse alphabet by the neutral relay at the home
station the distant pole-changer may reverse its battery
several times; the home pole-changer may do likewise, and the
home transmitter may increase and decrease the electromotive
force of the home battery repeatedly. Simultaneously,
and, of course, as a consequence of the foregoing
actions, the home neutral relay itself may have had its
magnetism reversed several times, and the SIGNAL, that is,
the dash, will have been made, partly by the home battery,
partly by the distant and home batteries combined, partly
by current on the main line, partly by current on the artificial
line, partly by the main-line `static' current, partly
by the condenser static current, and yet, on a well-adjusted
circuit the dash will have been produced on the quadruplex
sounder as clearly as any dash on an ordinary single-wire

We present a diagrammatic illustration of the Edison
quadruplex, battery key system, in Fig. 8, and refer the
reader to the above or other text-books if he desires to make
a close study of its intricate operations. Before finally
dismissing the quadruplex, and for the benefit of the inquiring
reader who may vainly puzzle over the intricacies of the circuits
shown in Fig. 8, a hint as to an essential difference between
the neutral relay, as used in the duplex and as used
in the quadruplex, may be given. With the duplex, as we
have seen, the current on the main line is changed in strength
only when both keys at OPPOSITE stations are closed together,
so that a current due to both batteries flows over the main
line. When a single message is sent from one station to the
other, or when both stations are sending messages that do
not conflict, only one battery or the other is connected to
the main line; but with the quadruplex, suppose one of the
operators, in New York for instance, is sending reversals of
current to Chicago; we can readily see how these changes
in polarity will operate the polar relay at the distant station,
but why will they not also operate the neutral relay at the
distant station as well? This difficulty was solved by dividing
the battery at each station into two unequal parts, the
smaller battery being always in circuit with the pole-changer
ready to have its polarity reversed on the main line to operate
the distant polar relay, but the spring retracting the
armature of the neutral relay is made so stiff as to resist
these weak currents. If, however, the transmitter is operated
at the same end, the entire battery is connected to the
main line, and the strength of this current is sufficient to
operate the neutral relay. Whether the part or all the battery
is alternately connected to or disconnected from the
main line by the transmitter, the current so varied in
strength is subject to reversal of polarity by the pole-changer;
but the variations in strength have no effect upon the distant
polar relay, because that relay being responsive to
changes in polarity of a weak current is obviously responsive
to corresponding changes in polarity of a powerful current.
With this distinction before him, the reader will have
no difficulty in following the circuits of Fig. 8, bearing always
in mind that by reason of the differential winding of the polar
and neutral relays, neither of the relays at one station will
respond to the home battery, and can only respond to the
distant battery--the polar relay responding when the polarity
of the current is reversed, whether the current be strong
or weak, and the neutral relay responding when the line-
current is increased, regardless of its polarity. It should
be added that besides the system illustrated in Fig. 8, which
is known as the differential principle, the quadruplex was
also arranged to operate on the Wheatstone bridge principle;
but it is not deemed necessary to enter into its details. The
underlying phenomena were similar, the difference consisting
largely in the arrangement of the circuits and apparatus.[24]

[24] Many of the illustrations in this article are reproduced
from American Telegraphy and Encyclopedia of the Telegraph,
by William Maver, Jr., by permission of Maver Publishing Company, New York.

Edison made another notable contribution to multiplex
telegraphy some years later in the Phonoplex. The name
suggests the use of the telephone, and such indeed is the
case. The necessity for this invention arose out of the
problem of increasing the capacity of telegraph lines employed
in "through" and "way" service, such as upon railroads.
In a railroad system there are usually two terminal
stations and a number of way stations. There is naturally
much intercommunication, which would be greatly curtailed
by a system having the capacity of only a single message
at a time. The duplexes above described could not
be used on a railroad telegraph system, because of the
necessity of electrically balancing the line, which, while
entirely feasible on a through line, would not be practicable
between a number of intercommunicating points. Edison's
phonoplex normally doubled the capacity of telegraph lines,
whether employed on way business or through traffic, but
in actual practice made it possible to obtain more than
double service. It has been in practical use for many years
on some of the leading railroads of the United States.

The system is a combination of telegraphic apparatus and
telephone receiver, although in this case the latter instrument
is not used in the generally understood manner. It
is well known that the diaphragm of a telephone vibrates
with the fluctuations of the current energizing the magnet
beneath it. If the make and break of the magnetizing current
be rapid, the vibrations being within the limits of the
human ear, the diaphragm will produce an audible sound;
but if the make and break be as slow as with ordinary Morse
transmission, the diaphragm will be merely flexed and return
to its original form without producing a sound. If, therefore,
there be placed in the same circuit a regular telegraph
relay and a special telephone, an operator may, by manipulating
a key, operate the relay (and its sounder) without
producing a sound in the telephone, as the makes and breaks
of the key are far below the limit of audibility. But if
through the same circuit, by means of another key suitably
connected there is sent the rapid changes in current from
an induction-coil, it will cause a series of loud clicks in the
telephone, corresponding to the signals transmitted; but
this current is too weak to affect the telegraph relay. It
will be seen, therefore, that this method of duplexing is
practiced, not by varying the strength or polarity, but by
sending TWO KINDS OF CURRENT over the wire. Thus, two sets
of Morse signals can be transmitted by two operators over
one line at the same time without interfering with each
other, and not only between terminal offices, but also between
a terminal office and any intermediate office, or between two
intermediate offices alone.



FROM the year 1848, when a Scotchman, Alexander Bain,
first devised a scheme for rapid telegraphy by automatic
methods, down to the beginning of the seventies, many other
inventors had also applied themselves to the solution of
this difficult problem, with only indifferent success. "Cheap
telegraphy" being the slogan of the time, Edison became
arduously interested in the subject, and at the end of three
years of hard work produced an entirely successful system,
a public test of which was made on December 11, 1873
when about twelve thousand (12,000) words were transmitted
over a single wire from Washington to New York.
in twenty-two and one-half minutes. Edison's system was
commercially exploited for several years by the Automatic
Telegraph Company, as related in the preceding narrative.

As a premise to an explanation of the principles involved
it should be noted that the transmission of telegraph messages
by hand at a rate of fifty words per minute is considered
a good average speed; hence, the availability of a
telegraph line, as thus operated, is limited to this capacity
except as it may be multiplied by two with the use of the
duplex, or by four, with the quadruplex. Increased rapidity
of transmission may, however, be accomplished by automatic
methods, by means of which, through the employment of
suitable devices, messages may be stamped in or upon a
paper tape, transmitted through automatically acting instruments,
and be received at distant points in visible characters,
upon a similar tape, at a rate twenty or more times
greater--a speed far beyond the possibilities of the human
hand to transmit or the ear to receive.

In Edison's system of automatic telegraphy a paper tape
was perforated with a series of round holes, so arranged and
spaced as to represent Morse characters, forming the words
of the message to be transmitted. This was done in a special
machine of Edison's invention, called a perforator, consisting
of a series of punches operated by a bank of keys--typewriter
fashion. The paper tape passed over a cylinder, and was
kept in regular motion so as to receive the perforations in
proper sequence.

The perforated tape was then placed in the transmitting
instrument, the essential parts of which were a metallic
drum and a projecting arm carrying two small wheels, which,
by means of a spring, were maintained in constant pressure
on the drum. The wheels and drum were electrically connected
in the line over which the message was to be sent.
current being supplied by batteries in the ordinary manner.

When the transmitting instrument was in operation, the
perforated tape was passed over the drum in continuous,
progressive motion. Thus, the paper passed between the
drum and the two small wheels, and, as dry paper is a non-
conductor, current was prevented from passing until a
perforation was reached. As the paper passed along, the wheels
dropped into the perforations, making momentary contacts
with the drum beneath and causing momentary impulses of
current to be transmitted over the line in the same way that
they would be produced by the manipulation of the telegraph
key, but with much greater rapidity. The perforations
being so arranged as to regulate the length of the
contact, the result would be the transmission of long and
short impulses corresponding with the dots and dashes of
the Morse alphabet.

The receiving instrument at the other end of the line was
constructed upon much the same general lines as the transmitter,
consisting of a metallic drum and reels for the paper
tape. Instead of the two small contact wheels, however, a
projecting arm carried an iron pin or stylus, so arranged
that its point would normally impinge upon the periphery
of the drum. The iron pin and the drum were respectively
connected so as to be in circuit with the transmission line
and batteries. As the principle involved in the receiving
operation was electrochemical decomposition, the paper
tape upon which the incoming message was to be received
was moistened with a chemical solution readily decom-
posable by the electric current. This paper, while still in
a damp condition, was passed between the drum and stylus
in continuous, progressive motion. When an electrical impulse
came over the line from the transmitting end, current
passed through the moistened paper from the iron pin, causing
chemical decomposition, by reason of which the iron would
be attacked and would mark a line on the paper. Such a
line would be long or short, according to the duration of the
electric impulse. Inasmuch as a succession of such impulses
coming over the line owed their origin to the perforations
in the transmitting tape, it followed that the resulting
marks upon the receiving tape would correspond thereto in
their respective lengths. Hence, the transmitted message
was received on the tape in visible dots and dashes representing
characters of the Morse alphabet.

The system will, perhaps, be better understood by reference
to the following diagrammatic sketch of its general principles:

Some idea of the rapidity of automatic telegraphy may
be obtained when we consider the fact that with the use
of Edison's system in the early seventies it was common
practice to transmit and receive from three to four thousand
words a minute over a single line between New York and
Philadelphia. This system was exploited through the use
of a moderately paid clerical force.

In practice, there was employed such a number of perforating
machines as the exigencies of business demanded.
Each machine was operated by a clerk, who translated the
message into telegraphic characters and prepared the transmitting
tape by punching the necessary perforations therein.
An expert clerk could perforate such a tape at the rate of
fifty to sixty words per minute. At the receiving end the
tape was taken by other clerks who translated the Morse
characters into ordinary words, which were written on
message blanks for delivery to persons for whom the messages
were intended.

This latter operation--"copying." as it was called--was
not consistent with truly economical business practice.
Edison therefore undertook the task of devising an improved
system whereby the message when received would
not require translation and rewriting, but would automatically
appear on the tape in plain letters and words, ready
for instant delivery.

The result was his automatic Roman letter system, the
basis for which included the above-named general principles
of perforated transmission tape and electrochemical
decomposition. Instead of punching Morse characters in the
transmission tape however, it was perforated with a series
of small round holes forming Roman letters. The verticals
of these letters were originally five holes high. The transmitting
instrument had five small wheels or rollers, instead
of two, for making contacts through the perforations and
causing short electric impulses to pass over the lines. At
first five lines were used to carry these impulses to the
receiving instrument, where there were five iron pins impinging
on the drum. By means of these pins the chemically
prepared tape was marked with dots corresponding to the
impulses as received, leaving upon it a legible record of the
letters and words transmitted.

For purposes of economy in investment and maintenance,
Edison devised subsequently a plan by which the number
of conducting lines was reduced to two, instead of five. The
verticals of the letters were perforated only four holes high,
and the four rollers were arranged in pairs, one pair being
slightly in advance of the other. There were, of course, only
four pins at the receiving instrument. Two were of iron and
two of tellurium, it being the gist of Edison's plan to effect
the marking of the chemical paper by one metal with a
positive current, and by the other metal with a negative
current. In the following diagram, which shows the theory
of this arrangement, it will be seen that both the transmitting
rollers and the receiving pins are arranged in pairs,
one pair in each case being slightly in advance of the other.
Of these receiving pins, one pair--1 and 3--are of iron, and
the other pair--2 and 4--of tellurium. Pins 1-2 and 3-4
are electrically connected together in other pairs, and then
each of these pairs is connected with one of the main lines
that run respectively to the middle of two groups of
batteries at the transmitting end. The terminals of these
groups of batteries are connected respectively to the four
rollers which impinge upon the transmitting drum, the
negatives being connected to 5 and 7, and the positives to 6
and 8, as denoted by the letters N and P. The transmitting
and receiving drums are respectively connected to earth.

In operation the perforated tape is placed on the
transmission drum, and the chemically prepared tape on the
receiving drum. As the perforated tape passes over the
transmission drum the advanced rollers 6 or 8 first close
the circuit through the perforations, and a positive current
passes from the batteries through the drum and down to the
ground; thence through the earth at the receiving end up
to the other drum and back to the batteries via the tellurium
pins 2 or 4 and the line wire. With this positive current the
tellurium pins make marks upon the paper tape, but the
iron pins make no mark. In the merest fraction of a second,
as the perforated paper continues to pass over the transmission
drum, the rollers 5 or 7 close the circuit through
other perforations and t e current passes in the opposite
direction, over the line wire, through pins 1 or 3, and
returns through the earth. In this case the iron pins mark
the paper tape, but the tellurium pins make no mark. It
will be obvious, therefore, that as the rollers are set so as to
allow of currents of opposite polarity to be alternately and
rapidly sent by means of the perforations, the marks upon
the tape at the receiving station will occupy their proper
relative positions, and the aggregate result will be letters
corresponding to those perforated in the transmission tape.

Edison subsequently made still further improvements in
this direction, by which he reduced the number of conducting
wires to one, but the principles involved were analogous
to the one just described.

This Roman letter system was in use for several years on
lines between New York, Philadelphia, and Washington,
and was so efficient that a speed of three thousand words a
minute was attained on the line between the two first-named

Inasmuch as there were several proposed systems of rapid
automatic telegraphy in existence at the time Edison entered
the field, but none of them in practical commercial
use, it becomes a matter of interest to inquire wherein they
were deficient, and what constituted the elements of Edison's

The chief difficulties in the transmission of Morse
characters had been two in number, the most serious of which
was that on the receiving tape the characters would be
prolonged and run into one another, forming a draggled line and
thus rendering the message unintelligible. This arose from
the fact that, on account of the rapid succession of the electric
impulses, there was not sufficient time between them for
the electric action to cease entirely. Consequently the line
could not clear itself, and became surcharged, as it were;
the effect being an attenuated prolongation of each impulse
as manifested in a weaker continuation of the mark on the
tape, thus making the whole message indistinct. These
secondary marks were called "tailings."

For many years electricians had tried in vain to overcome
this difficulty. Edison devoted a great deal of thought
and energy to the question, in the course of which he
experimented through one hundred and twenty consecutive
nights, in the year 1873, on the line between New York and
Washington. His solution of the problem was simple but
effectual. It involved the principle of inductive compensation.
In a shunt circuit with the receiving instrument he
introduced electromagnets. The pulsations of current
passed through the helices of these magnets, producing an
augmented marking effect upon the receiving tape, but
upon the breaking of the current, the magnet, in discharging
itself of the induced magnetism, would set up momentarily
a counter-current of opposite polarity. This neutralized
the "tailing" effect by clearing the line between
pulsations, thus allowing the telegraphic characters to be
clearly and distinctly outlined upon the tape. Further
elaboration of this method was made later by the addition
of rheostats, condensers, and local opposition batteries on
long lines.

The other difficulty above referred to was one that had
also occupied considerable thought and attention of many
workers in the field, and related to the perforating of the
dash in the transmission tape. It involved mechanical
complications that seemed to be insurmountable, and up to the
time Edison invented his perforating machine no really good
method was available. He abandoned the attempt to cut
dashes as such, in the paper tape, but instead punched three
round holes so arranged as to form a triangle. A concrete
example is presented in the illustration below, which shows
a piece of tape with perforations representing the word

The philosophy of this will be at once perceived when it
is remembered that the two little wheels running upon the
drum of the transmitting instrument were situated side by
side, corresponding in distance to the two rows of holes.
When a triangle of three holes, intended to form the dash,
reached the wheels, one of them dropped into a lower hole.
Before it could get out, the other wheel dropped into the hole
at the apex of the triangle, thus continuing the connection,
which was still further prolonged by the first wheel dropping
into the third hole. Thus, an extended contact was made,
which, by transmitting a long impulse, resulted in the marking
of a dash upon the receiving tape.

This method was in successful commercial use for some
time in the early seventies, giving a speed of from three to
four thousand words a minute over a single line, but later
on was superseded by Edison's Roman letter system, above
referred to.

The subject of automatic telegraphy received a vast
amount of attention from inventors at the time it was in
vogue. None was more earnest or indefatigable than Edison,
who, during the progress of his investigations, took out
thirty-eight patents on various inventions relating thereto,
some of them covering chemical solutions for the receiving
paper. This of itself was a subject of much importance
and a vast amount of research and labor was expended
upon it. In the laboratory note-books there are recorded
thousands of experiments showing that Edison's investigations
not only included an enormous number of chemical
salts and compounds, but also an exhaustive variety of
plants, flowers, roots, herbs, and barks.

It seems inexplicable at first view that a system of telegraphy
sufficiently rapid and economical to be practically
available for important business correspondence should have
fallen into disuse. This, however, is made clear--so far as
concerns Edison's invention at any rate--in Chapter VIII
of the preceding narrative.



ALTHOUGH Mr. Edison has taken no active part in the
development of the more modern wireless telegraphy, and
his name has not occurred in connection therewith, the
underlying phenomena had been noted by him many years in
advance of the art, as will presently be explained. The
authors believe that this explanation will reveal a status of
Edison in relation to the subject that has thus far been unknown
to the public.

While the term "wireless telegraphy," as now applied to
the modern method of electrical communication between distant
points without intervening conductors, is self-explanatory,
it was also applicable, strictly speaking, to the previous
art of telegraphing to and from moving trains, and between
points not greatly remote from each other, and not connected
together with wires.

The latter system (described in Chapter XXIII and in a
succeeding article of this Appendix) was based upon the
phenomena of electromagnetic or electrostatic induction between
conductors separated by more or less space, whereby
electric impulses of relatively low potential and low frequency
set up in. one conductor were transmitted inductively
across the air to another conductor, and there received
through the medium of appropriate instruments connected

As distinguished from this system, however, modern wireless
telegraphy--so called--has its basis in the utilization of
electric or ether waves in free space, such waves being set up
by electric oscillations, or surgings, of comparatively high
potential and high frequency, produced by the operation of
suitable electrical apparatus. Broadly speaking, these oscillations
arise from disruptive discharges of an induction
coil, or other form of oscillator, across an air-gap, and their
character is controlled by the manipulation of a special type
of circuit-breaking key, by means of which long and short
discharges are produced. The electric or etheric waves
thereby set up are detected and received by another special
form of apparatus more or less distant, without any intervening
wires or conductors.

In November, 1875, Edison, while experimenting in his
Newark laboratory, discovered a new manifestation of electricity
through mysterious sparks which could be produced
under conditions unknown up to that time. Recognizing
at once the absolutely unique character of the phenomena,
he continued his investigations enthusiastically over two
mouths, finally arriving at a correct conclusion as to the
oscillatory nature of the hitherto unknown manifestations.
Strange to say, however, the true import and practical
applicability of these phenomena did not occur to his mind.
Indeed, it was not until more than TWELVE YEARS AFTERWARD,
in 1887, upon the publication of the notable work of Prof.
H. Hertz proving the existence of electric waves in free space,
that Edison realized the fact that the fundamental principle
of aerial telegraphy had been within his grasp in the winter
of 1875; for although the work of Hertz was more profound
and mathematical than that of Edison, the principle involved
and the phenomena observed were practically identical--in
fact, it may be remarked that some of the methods and experimental
apparatus were quite similar, especially the "dark
box" with micrometer adjustment, used by both in observing
the spark.[25]

[25] During the period in which Edison exhibited his lighting system at
the Paris Exposition in 1881, his representative, Mr. Charles Batchelor,
repeated Edison's remarkable experiments of the winter of 1875 for the
benefit of a great number of European savants, using with other apparatus
the original "dark box" with micrometer adjustment.

There is not the slightest intention on the part of the
authors to detract in the least degree from the brilliant work
of Hertz, but, on the contrary, to ascribe to him the honor
that is his due in having given mathematical direction and
certainty to so important a discovery. The adaptation of
the principles thus elucidated and the subsequent development
of the present wonderful art by Marconi, Branly,
Lodge, Slaby, and others are now too well known to call for
further remark at this place.

Strange to say, that although Edison's early experiments
in "etheric force" called forth extensive comment and
discussion in the public prints of the period, they seemed to
have been generally overlooked when the work of Hertz was
published. At a meeting of the Institution of Electrical
Engineers, held in London on May 16, 1889, at which there
was a discussion on the celebrated paper of Prof. (Sir) Oliver
Lodge on "Lightning Conductors," however; the chairman,
Sir William Thomson (Lord Kelvin), made the following

"We all know how Faraday made himself a cage six feet
in diameter, hung it up in mid-air in the theatre of the
Royal Institution, went into it, and, as he said, lived in it
and made experiments. It was a cage with tin-foil hanging
all round it; it was not a complete metallic enclosing shell.
Faraday had a powerful machine working in the neighborhood,
giving all varieties of gradual working-up and discharges
by `impulsive rush'; and whether it was a sudden
discharge of ordinary insulated conductors, or of Leyden
jars in the neighborhood outside the cage, or electrification
and discharge of the cage itself, he saw no effects on his
most delicate gold-leaf electroscopes in the interior. His attention
was not directed to look for Hertz sparks, or probably
he might have found them in the interior. Edison seems to
have noticed something of the kind in what he called the
etheric force. His name `etheric' may, thirteen years ago,
have seemed to many people absurd. But now we are all
beginning to call these inductive phenomena `etheric.' "

With these preliminary observations, let us now glance
briefly at Edison's laboratory experiments, of which mention
has been made.

Oh the first manifestation of the unusual phenomena in
November, 1875, Edison's keenness of perception led him
at once to believe that he had discovered a new force. Indeed,
the earliest entry of this discovery in the laboratory
note-book bore that caption. After a few days of further
experiment and observation, however, he changed it to
"Etheric Force," and the further records thereof (all in Mr.
Batchelor's handwriting) were under that heading.

The publication of Edison's discovery created considerable
attention at the time, calling forth a storm of general
ridicule and incredulity. But a few scientific men of the
period, whose experimental methods were careful and exact,
corroborated his deductions after obtaining similar phenomena
by repeating his experiments with intelligent precision.
Among these was the late Dr. George M. Beard, a
noted physicist, who entered enthusiastically into the
investigation, and, in addition to a great deal of independent
experiment, spent much time with Edison at his laboratory.
Doctor Beard wrote a treatise of some length on the subject,
in which he concurred with Edison's deduction that the
phenomena were the manifestation of oscillations, or rapidly
reversing waves of electricity, which did not respond to the
usual tests. Edison had observed the tendency of this force
to diffuse itself in various directions through the air and
through matter, hence the name "Etheric" that he had
provisionally applied to it.

Edison's laboratory notes on this striking investigation
are fascinating and voluminous, but cannot be reproduced
in full for lack of space. In view of the later practical
application of the principles involved, however, the reader will
probably be interested in perusing a few extracts therefrom
as illustrated by facsimiles of the original sketches from the
laboratory note-book.

As the full significance of the experiments shown by these
extracts may not be apparent to a lay reader, it may be
stated by way of premise that, ordinarily, a current only
follows a closed circuit. An electric bell or electric light is a
familiar instance of this rule. There is in each case an open
(wire) circuit which is closed by pressing the button or turning
the switch, thus making a complete and uninterrupted
path in which the current may travel and do its work. Until
the time of Edison's investigations of 1875, now under
consideration, electricity had never been known to manifest
itself except through a closed circuit. But, as the reader
will see from the following excerpts, Edison discovered a
hitherto unknown phenomenon--namely, that under certain
conditions the rule would be reversed and electricity would
pass through space and through matter entirely unconnected
with its point of origin. In other words, he had found the
forerunner of wireless telegraphy. Had he then realized the
full import of his discovery, all he needed was to increase the
strength of the waves and to provide a very sensitive detector,
like the coherer, in order to have anticipated the principal
developments that came many years afterward. With
these explanatory observations, we will now turn to the
excerpts referred to, which are as follows:

"November 22, 1875. New Force.--In experimenting
with a vibrator magnet consisting of a bar of Stubb's steel
fastened at one end and made to vibrate by means of a
magnet, we noticed a spark coming from the cores of the
magnet. This we have noticed often in relays, in stock-
printers, when there were a little iron filings between the
armature and core, and more often in our new electric pen,
and we have always come to the conclusion that it was
caused by strong induction. But when we noticed it on this
vibrator it seemed so strong that it struck us forcibly there
might be something more than induction. We now found
that if we touched any metallic part of the vibrator or magnet
we got the spark. The larger the body of iron touched to
the vibrator the larger the spark. We now connected a
wire to X, the end of the vibrating rod, and we found we
could get a spark from it by touching a piece of iron to it,
and one of the most curious phenomena is that if you turn
the wire around on itself and let the point of the wire touch
any other portion of itself you get a spark. By connecting
X to the gas-pipe we drew sparks from the gas-pipes in any
part of the room by drawing an iron wire over the brass jet
of the cock. This is simply wonderful, and a good proof
that the cause of the spark is a TRUE UNKNOWN FORCE."

"November 23, 1815. New Force.--The following very
curious result was obtained with it. The vibrator shown in
Fig. 1 and battery were placed on insulated stands; and a
wire connected to X (tried both copper and iron) carried
over to the stove about twenty feet distant. When the end
of the wire was rubbed on the stove it gave out splendid
sparks. When permanently connected to the stove, sparks
could be drawn from the stove by a piece of wire held in
the hand. The point X of vibrator was now connected to
the gas-pipe and still the sparks could be drawn from the

. . . . . . . . .

"Put a coil of wire over the end of rod X and passed the
ends of spool through galvanometer without affecting it in
any way. Tried a 6-ohm spool add a 200-ohm. We now
tried all the metals, touching each one in turn to the point
X." [Here follows a list of metals and the character of spark
obtained with each.]

. . . . . . . . .

"By increasing the battery from eight to twelve cells we
get a spark when the vibrating magnet is shunted with 3
ohms. Cannot taste the least shock at B, yet between carbon
points the spark is very vivid. As will be seen, X has no
connection with anything. With a glass rod four feet long, well
rubbed with a piece of silk over a hot stove, with a piece
of battery carbon secured to one end, we received vivid
sparks into the carbon when the other end was held in the
hand with the handkerchief, yet the galvanometer, chemical
paper, the sense of shock in the tongue, and a gold-leaf
electroscope which would diverge at two feet from a half-
inch spark plate-glass machine were not affected in the
least by it.

"A piece of coal held to the wire showed faint sparks.

"We had a box made thus: whereby two points could be
brought together within a dark box provided with an eyepiece.
The points were iron, and we found the sparks were
very irregular. After testing some time two lead-pencils
found more regular and very much more vivid. We then
substituted the graphite points instead of iron."[26]

[26] The dark box had micrometer screws for delicate adjustment of the carbon
points, and was thereafter largely used in this series of investigations for
better study of the spark. When Mr. Edison's experiments were repeated by Mr.
Batchelor, who represented him at the Paris Exposition of 1881, the dark box
was employed for a similar purpose.

. . . . . . . . .

After recording a considerable number of other experiments,
the laboratory notes go on to state:

"November 30, 1875. Etheric Force.--We found the
addition of battery to the Stubb's wire vibrator greatly
increased the volume of spark. Several persons could obtain
sparks from the gas-pipes at once, each spark being equal
in volume and brilliancy to the spark drawn by a single
person.... Edison now grasped the (gas) pipe, and with the
other hand holding a piece of metal, he touched several
other metallic substances, obtained sparks, showing that the
force passed through his body."

. . . . . . . . .

"December 3, 1875. Etheric Force.--Charley Edison
hung to the gas-pipe with feet above the floor, and with a
knife got a spark from the pipe he was hanging on. We now
took the wire from the vibrator in one hand and stood on a
block of paraffin eighteen inches square and six inches thick;
holding a knife in the other hand, we drew sparks from the
stove-pipe. We now tried the crucial test of passing the
etheric current through the sciatic nerve of a frog just killed.
Previous to trying, we tested its sensibility by the current
from a single Bunsen cell. We put in resistance up to
500,000 ohms, and the twitching was still perceptible. We
tried the induced current from our induction coil having one
cell on primary,, the spark jumping about one-fiftieth of an
inch, the terminal of the secondary connected to the frog
and it straightened out with violence. We arranged frog's
legs to pass etheric force through. We placed legs on an
inverted beaker, and held the two ends of the wires on glass
rods eight inches long. On connecting one to the sciatic
nerve and the other to the fleshy part of the leg no movement
could be discerned, although brilliant sparks could be ob-
tained on the graphite points when the frog was in circuit.
Doctor Beard was present when this was tried."

. . . . . . . . .

"December 5, 1875. Etheric Force.--Three persons
grasping hands and standing upon blocks of paraffin twelve
inches square and six thick drew sparks from the adjoining
stove when another person touched the sounder with any
piece of metal.... A galvanoscopic frog giving contractions
with one cell through two water rheostats was then placed
in circuit. When the wires from the vibrator and the gas-
pipe were connected, slight contractions were noted, sometimes
very plain and marked, showing the apparent presence
of electricity, which from the high insulation seemed improbable.
Doctor Beard, who was present, inferred from
the way the leg contracted that it moved on both opening
and closing the circuit. To test this we disconnected the
wire between the frog and battery, and placed, instead of a
vibrating sounder, a simple Morse key and a sounder taking
the `etheric' from armature. The spark was now tested in
dark box and found to be very strong. It was then connected
to the nerves of the frog, BUT NO MOVEMENT OF ANY KIND
and power of the spark were undiminished. The thought
then occurred to Edison that the movement of the frog was
due to mechanical vibrations from the vibrator (which gives
probably two hundred and fifty vibrations per second), passing
through the wires and irritating the sensitive nerves of
the frog. Upon disconnecting the battery wires and holding
a tuning-fork giving three hundred and twenty-six vibrations
per second to the base of the sounder, the vibrations over
the wire made the frog contract nearly every time.... The
contraction of the frog's legs may with considerable safety
be said to be caused by these mechanical vibrations being
transmitted through the conducting wires."

Edison thought that the longitudinal vibrations caused
by the sounder produced a more marked effect, and proceeded
to try out his theory. The very next entry in the
laboratory note-book bears the same date as the above
(December 5, 1875), and is entitled "Longitudinal Vibrations,"
and reads as follows:

"We took a long iron wire one-sixteenth of an inch in diameter
and rubbed it lengthways with a piece of leather with
resin on for about three feet, backward and forward. About
ten feet away we applied the wire to the back of the neck
and it gives a horrible sensation, showing the vibrations
conducted through the wire."

. . . . . . . . .

The following experiment illustrates notably the movement
of the electric waves through free space:

"December 26, 1875. Etheric Force.--An experiment
tried to-night gives a curious result. A is a vibrator, B, C,
D, E are sheets of tin-foil hung on insulating stands. The
sheets are about twelve by eight inches. B and C are
twenty-six inches apart, C and D forty-eight inches and D
and E twenty-six inches. B is connected to the vibrator
and E to point in dark box, the other point to ground. We
received sparks at intervals, although insulated by such

With the above our extracts must close, although we have
given but a few of the interesting experiments tried at the
time. It will be noticed, however, that these records show
much progression in a little over a month. Just after the
item last above extracted, the Edison shop became greatly
rushed on telegraphic inventions, and not many months
afterward came the removal to Menlo Park; hence the
etheric-force investigations were side-tracked for other
matters deemed to be more important at that time.

Doctor Beard in his previously mentioned treatise refers,
on page 27, to the views of others who have repeated Edison's
experiments and observed the phenomena, and in a foot-note

"Professor Houston, of Philadelphia, among others, has
repeated some of these physical experiments, has adopted
in full and after but a partial study of the subject, the
hypothesis of rapidly reversed electricity as suggested in
my letter to the Tribune of December 8th, and further claims
priority of discovery, because he observed the spark of this
when experimenting with a Ruhmkorff coil four years ago.
To this claim, if it be seriously entertained, the obvious reply
is that thousands of persons, probably, had seen this spark
before it was DISCOVERED by Mr. Edison; it had been seen by
Professor Nipher, who supposed, and still supposes, it is the
spark of the extra current; it has been seen by my friend,
Prof. J. E. Smith, who assumed, as he tells me, without
examination, that it was inductive electricity breaking
through bad insulation; it had been seen, as has been stated,
by Mr. Edison many times before he thought it worthy of
study, it was undoubtedly seen by Professor Houston, who,
like so many others, failed to even suspect its meaning and
thus missed an important discovery. The honor of a scientific
discovery belongs, not to him who first sees a thing, but
to him who first sees it with expert eyes; not to him even
who drops an original suggestion, but to him who first makes,
that suggestion fruitful of results. If to see with the eyes
a phenomenon is to discover the law of which that phenomenon
is a part, then every schoolboy who, before the time
of Newton, ever saw an apple fall, was a discoverer of the
law of gravitation...."

Edison took out only one patent on long-distance telegraphy
without wires. While the principle involved therein
(induction) was not precisely analogous to the above, or to
the present system of wireless telegraphy, it was a step forward
in the progress of the art. The application was filed
May 23, 1885, at the time he was working on induction
telegraphy (two years before the publication of the work of
Hertz), but the patent (No. 465,971) was not issued until
December 29, 1891. In 1903 it was purchased from him by
the Marconi Wireless Telegraph Company. Edison has always
had a great admiration for Marconi and his work, and
a warm friendship exists between the two men. During the
formative period of the Marconi Company attempts were
made to influence Edison to sell this patent to an opposing
concern, but his regard for Marconi and belief in the
fundamental nature of his work were so strong that he refused
flatly, because in the hands of an enemy the patent might be
used inimically to Marconi's interests.

Edison's ideas, as expressed in the specifications of this
patent, show very clearly the close analogy of his system to
that now in vogue. As they were filed in the Patent Office
several years before the possibility of wireless telegraphy
was suspected, it will undoubtedly be of interest to give the
following extract therefrom:

"I have discovered that if sufficient elevation be obtained
to overcome the curvature of the earth's surface and to reduce
to the minimum the earth's absorption, electric telegraphing
or signalling between distant points can be carried
on by induction without the use of wires connecting such
distant points. This discovery is especially applicable to
telegraphing across bodies of water, thus avoiding the use
of submarine cables, or for communicating between vessels
at sea, or between vessels at sea and points on land, but it
is also applicable to electric communication between distant
points on land, it being necessary, however, on land (with
the exception of communication over open prairie) to increase
the elevation in order to reduce to the minimum the
induction-absorbing effect of houses, trees, and elevations in
the land itself. At sea from an elevation of one hundred
feet I can communicate electrically a great distance, and
since this elevation or one sufficiently high can be had by
utilizing the masts of ships, signals can be sent and received
between ships separated a considerable distance, and by
repeating the signals from ship to ship communication can
be established between points at any distance apart or
across the largest seas and even oceans. The collision of
ships in fogs can be prevented by this character of signalling,
by the use of which, also, the safety of a ship in approaching
a dangerous coast in foggy weather can be assured. In
communicating between points on land, poles of great height
can be used, or captive balloons. At these elevated points,
whether upon the masts of ships, upon poles or balloons,
condensing surfaces of metal or other conductor of electricity
are located. Each condensing surface is connected with
earth by an electrical conducting wire. On land this earth
connection would be one of usual character in telegraphy.
At sea the wire would run to one or more metal plates on
the bottom of the vessel, where the earth connection would
be made with the water. The high-resistance secondary
circuit of an induction coil is located in circuit between the
condensing surface and the ground. The primary circuit of
the induction coil includes a battery and a device for transmitting
signals, which may be a revolving circuit-breaker
operated continually by a motor of any suitable kind, either
electrical or mechanical, and a key normally short-circuiting
the circuit-breaker or secondary coil. For receiving signals
I locate in said circuit between the condensing surface and
the ground a diaphragm sounder, which is preferably one of
my electromotograph telephone receivers. The key normally
short-circuiting the revolving circuit-breaker, no impulses
are produced in the induction coil until the key is
depressed, when a large number of impulses are produced in
the primary, and by means of the secondary corresponding
impulses or variations in tension are produced at the elevated
condensing surface, producing thereat electrostatic impulses.
These electrostatic impulses are transmitted inductively to
the elevated condensing surface at the distant point, and are
made audible by the electromotograph connected in the
ground circuit with such distant condensing surface."

The accompanying illustrations are reduced facsimiles of
the drawings attached to the above patent, No. 465,971.



IN solving a problem that at the time was thought to be
insurmountable, and in the adaptability of its principles to
the successful overcoming of apparently insuperable difficulties
subsequently arising in other lines of work, this invention
is one of the most remarkable of the many that
Edison has made in his long career as an inventor.

The object primarily sought to be accomplished was the
repeating of telegraphic signals from a distance without the
aid of a galvanometer or an electromagnetic relay, to overcome
the claims of the Page patent referred to in the preceding
narrative. This object was achieved in the device
described in Edison's basic patent No. 158,787, issued
January 19, 1875, by the substitution of friction and anti-
friction for the presence and absence of magnetism in a
regulation relay.

It may be observed, parenthetically, for the benefit of the
lay reader, that in telegraphy the device known as the relay
is a receiving instrument containing an electromagnet
adapted to respond to the weak line-current. Its armature
moves in accordance with electrical impulses, or signals,
transmitted from a distance, and, in so responding, operates
mechanically to alternately close and open a separate local
circuit in which there is a sounder and a powerful battery.
When used for true relaying purposes the signals received
from a distance are in turn repeated over the next section
of the line, the powerful local battery furnishing current for
this purpose. As this causes a loud repetition of the original
signals, it will be seen that relaying is an economic method
of extending a telegraph circuit beyond the natural limits of
its battery power.

At the time of Edison's invention, as related in Chapter
IX of the preceding narrative, there existed no other known
method than the one just described for the repetition of
transmitted signals, thus limiting the application of
telegraphy to the pleasure of those who might own any patent
controlling the relay, except on simple circuits where a
single battery was sufficient. Edison's previous discovery
of differential friction of surfaces through electrochemical
decomposition was now adapted by him to produce motion
at the end of a circuit without the intervention of an electromagnet.
In other words, he invented a telegraph instrument
having a vibrator controlled by electrochemical
decomposition, to take the place of a vibrating armature
operated by an electromagnet, and thus opened an entirely
new and unsuspected avenue in the art.

Edison's electromotograph comprised an ingeniously
arranged apparatus in which two surfaces, normally in contact
with each other, were caused to alternately adhere by
friction or slip by reason of electrochemical decomposition.
One of these surfaces consisted of a small drum or cylinder
of chalk, which was kept in a moistened condition with a
suitable chemical solution, and adapted to revolve
continuously by clockwork. The other surface consisted of a
small pad which rested with frictional pressure on the
periphery of the drum. This pad was carried on the end of a
vibrating arm whose lateral movement was limited between
two adjustable points. Normally, the frictional pressure
between the drum and pad would carry the latter with the
former as it revolved, but if the friction were removed a
spring on the end of the vibrator arm would draw it back to
its starting-place.

In practice, the chalk drum was electrically connected
with one pole of an incoming telegraph circuit, and the
vibrating arm and pad with the other pole. When the drum
rotated, the friction of the pad carried the vibrating arm
forward, but an electrical impulse coming over the line would
decompose the chemical solution with which the drum was
moistened, causing an effect similar to lubrication, and thus
allowing the pad to slip backward freely in response to the
pull of its retractile spring. The frictional movements of
the pad with the drum were comparatively long or short,
and corresponded with the length of the impulses sent in over
the line. Thus, the transmission of Morse dots and dashes
by the distant operator resulted in movements of corresponding
length by the frictional pad and vibrating arm.

This brings us to the gist of the ingenious way in which
Edison substituted the action of electrochemical decomposition
for that of the electromagnet to operate a relay.
The actual relaying was accomplished through the medium
of two contacts making connection with the local or relay
circuit. One of these contacts was fixed, while the other
was carried by the vibrating arm; and, as the latter made
its forward and backward movements, these contacts were
alternately brought together or separated, thus throwing in
and out of circuit the battery and sounder in the local circuit
and causing a repetition of the incoming signals. The
other side of the local circuit was permanently connected to
an insulated block on the vibrator. This device not only
worked with great rapidity, but was extremely sensitive,
and would respond to currents too weak to affect the most
delicate electromagnetic relay. It should be stated that
Edison did not confine himself to the working of the electromotograph
by the slipping of surfaces through the action of
incoming current, but by varying the character of the surfaces
in contact the frictional effect might be intensified by
the electrical current. In such a case the movements would
be the reverse of those above indicated, but the end sought
--namely, the relaying of messages--would be attained with
the same certainty.

While the principal object of this invention was to accomplish
the repetition of signals without the aid of an electromagnetic
relay, the instrument devised by Edison was
capable of use as a recorder also, by employing a small wheel
inked by a fountain wheel and attached to the vibrating arm
through suitable mechanism. By means of this adjunct the
dashes and dots of the transmitted impulses could be recorded
upon a paper ribbon passing continuously over the drum.

The electromotograph is shown diagrammatically in Figs.
1 and 2, in plan and vertical section respectively. The
reference letters in each case indicate identical parts: A
being the chalk drum, B the paper tape, C the auxiliary
cylinder, D the vibrating arm, E the frictional pad, F the
spring, G and H the two contacts, I and J the two wires leading
to local circuit, K a battery, and L an ordinary telegraph
key. The two last named, K and L, are shown to make the
sketch complete but in practice would be at the transmitting
end, which might be hundreds of miles away. It
will be understood, of course, that the electromotograph is
a receiving and relaying instrument.

Another notable use of the electromotograph principle
was in its adaptation to the receiver in Edison's loud-speaking
telephone, on which United States Patent No. 221,957
was issued November 25, 1879. A chalk cylinder moistened
with a chemical solution was revolved by hand or a small
motor. Resting on the cylinder was a palladium-faced pen
or spring, which was attached to a mica diaphragm in a
resonator. The current passed from the main line through
the pen to the chalk and to the battery. The sound-waves
impinging upon the distant transmitter varied the resistance
of the carbon button therein, thus causing corresponding
variations in the strength of the battery current. These
variations, passing through the chalk cylinder produced
more or less electrochemical decomposition, which in turn
caused differences of adhesion between the pen and cylinder
and hence gave rise to mechanical vibrations of the diaphragm
by reason of which the speaker's words were reproduced.
Telephones so operated repeated speaking and
singing in very loud tones. In one instance, spoken words
and the singing of songs originating at a distance were heard
perfectly by an audience of over five thousand people.

The loud-speaking telephone is shown in section,
diagrammatically, in the sketch (Fig. 3), in which A is the chalk
cylinder mounted on a shaft, B. The palladium-faced pen
or spring, C, is connected to diaphragm D. The instrument
in its commercial form is shown in Fig. 4.



ON April 27, 1877, Edison filed in the United States Patent
Office an application for a patent on a telephone, and on
May 3, 1892, more than fifteen years afterward, Patent No.
474,230 was granted thereon. Numerous other patents have
been issued to him for improvements in telephones, but the
one above specified may be considered as the most important
of them, since it is the one that first discloses the principle
of the carbon transmitter.

This patent embodies but two claims, which are as follows:

"1. In a speaking-telegraph transmitter, the combination
of a metallic diaphragm and disk of plumbago or equivalent
material, the contiguous faces of said disk and diaphragm
being in contact, substantially as described.

"2. As a means for effecting a varying surface contact
in the circuit of a speaking-telegraph transmitter, the combination
of two electrodes, one of plumbago or similar material,
and both having broad surfaces in vibratory contact
with each other, substantially as described."

The advance that was brought about by Edison's carbon
transmitter will be more apparent if we glance first at the
state of the art of telephony prior to his invention.

Bell was undoubtedly the first inventor of the art of transmitting
speech over an electric circuit, but, with his particular
form of telephone, the field was circumscribed. Bell's
telephone is shown in the diagrammatic sectional sketch
(Fig. 1).

In the drawing M is a bar magnet contained in the rubber
case, L. A bobbin, or coil of wire, B, surrounds one end of
the magnet. A diaphragm of soft iron is shown at D, and
E is the mouthpiece. The wire terminals of the coil, B,
connect with the binding screws, C C.

The next illustration shows a pair of such telephones
connected for use, the working parts only being designated by
the above reference letters.

It will be noted that the wire terminals are here put to
their proper uses, two being joined together to form a line
of communication, and the other two being respectively connected
to "ground."

Now, if we imagine a person at each one of the instruments
(Fig. 2) we shall find that when one of them speaks
the sound vibrations impinge upon the diaphragm and cause
it to act as a vibrating armature. By reason of its vibrations,
this diaphragm induces very weak electric impulses
in the magnetic coil. These impulses, according to Bell's
theory, correspond in form to the sound-waves, and, passing
over the line, energize the magnet coil at the receiving end,
thus giving rise to corresponding variations in magnetism
by reason of which the receiving diaphragm is similarly vibrated
so as to reproduce the sounds. A single apparatus
at each end is therefore sufficient, performing the double
function of transmitter and receiver. It will be noticed that
in this arrangement no battery is used The strength of the
impulses transmitted is therefore limited to that of the
necessarily weak induction currents generated by the original
sounds minus any loss arising by reason of resistance in the

Edison's carbon transmitter overcame this vital or limiting
weakness by providing for independent power on the transmission
circuit, and by introducing the principle of varying the
resistance of that circuit with changes in the pressure. With
Edison's telephone there is used a closed circuit on which a
battery current constantly flows, and in that circuit is a
pair of electrodes, one or both of which is carbon. These
electrodes are always in contact with a certain initial pressure,
so that current will be always flowing over the circuit. One
of the electrodes is connected with the diaphragm on which
the sound-waves impinge, and the vibrations of this diaphragm
cause corresponding variations in pressure between
the electrodes, and thereby effect similar variations in the
current which is passing over the line to the receiving end.
This current, flowing around the receiving magnet, causes
corresponding impulses therein, which, acting upon its
diaphragm, effect a reproduction of the original vibrations
and hence of the original sounds.

In other words, the essential difference is that with Bell's
telephone the sound-waves themselves generate the electric
impulses, which are therefore extremely faint. With Edison's
telephone the sound-waves simply actuate an electric
valve, so to speak, and permit variations in a current of any
desired strength.

A second distinction between the two telephones is this:
With the Bell apparatus the very weak electric impulses generated
by the vibration of the transmitting diaphragm pass
over the entire line to the receiving end, and, in consequence,
the possible length of line is limited to a few miles, even
under ideal conditions. With Edison's telephone the battery
current does not flow on the main line, but passes
through the primary circuit of an induction-coil, from the
secondary of which corresponding impulses of enormously
higher potential are sent out on the main line to the receiving
end. In consequence, the line may be hundreds of miles
in length. No modern telephone system is in use to-day
that does not use these characteristic features: the varying
resistance and the induction-coil. The system inaugurated
by Edison is shown by the diagram (Fig. 3), in which the car-
bon transmitter, the induction-coil, the line, and the distant
receiver are respectively indicated.

In Fig. 4 an early form of the Edison carbon transmitter is
represented in sectional view.

The carbon disk is represented by the black portion, E,
near the diaphragm, A, placed between two platinum plates
D and G, which are connected in the battery circuit, as shown
by the lines. A small piece of rubber tubing, B, is attached
to the centre of the metallic diaphragm, and presses lightly
against an ivory piece, F, which is placed directly over one
of the platinum plates. Whenever, therefore, any motion is
given to the diaphragm, it is immediately followed by a
corresponding pressure upon the carbon, and by a change of
resistance in the latter, as described above.

It is interesting to note the position which Edison occupies
in the telephone art from a legal standpoint. To this end
the reader's attention is called to a few extracts from a
decision of Judge Brown in two suits brought in the United
States Circuit Court, District of Massachusetts, by the American
Bell Telephone Company against the National Telephone
Manufacturing Company, et al., and Century Telephone
Company, et al., reported in Federal Reporter, 109, page 976,
et seq. These suits were brought on the Berliner patent,
which, it was claimed, covered broadly the electrical transmission
of speech by variations of pressure between opposing
electrodes in constant contact. The Berliner patent was
declared invalid, and in the course of a long and exhaustive
opinion, in which the state of art and the work of Bell, Edison,
Berliner, and others was fully discussed, the learned Judge
made the following remarks: "The carbon electrode was the
invention of Edison.... Edison preceded Berliner in the transmission
of speech.... The carbon transmitter was an experimental
invention of a very high order of merit.... Edison,
by countless experiments, succeeded in advancing the art.
. . . That Edison did produce speech with solid electrodes
before Berliner is clearly proven.... The use of carbon in a
transmitter is, beyond controversy, the invention of Edison.
Edison was the first to make apparatus in which carbon was
used as one of the electrodes.... The carbon transmitter
displaced Bell's magnetic transmitter, and, under several
forms of construction, remains the only commercial
instrument.... The advance in the art was due to the carbon
electrode of Edison.... It is conceded that the Edison
transmitter as apparatus is a very important invention.... An
immense amount of painstaking and highly ingenious experiment
preceded Edison's successful result. The discovery of
the availability of carbon was unquestionably invention,
and it resulted in the `first practical success in the art.' "



THIS interesting and remarkable device is one of Edison's
many inventions not generally known to the public at large,
chiefly because the range of its application has been limited
to the higher branches of science. He never applied for a
patent on the instrument, but dedicated it to the public.

The device was primarily intended for use in detecting and
measuring infinitesimal degrees of temperature, however
remote, and its conception followed Edison's researches on
the carbon telephone transmitter. Its principle depends
upon the variable resistance of carbon in accordance with
the degree of pressure to which it is subjected. By means
of this instrument, pressures that are otherwise inappreciable
and undiscoverable may be observed and indicated.

The detection of small variations of temperatures is
brought about through the changes which heat or cold will
produce in a sensitive material placed in contact with a
carbon button, which is put in circuit with a battery and
delicate galvanometer. In the sketch (Fig. 1) there is illustrated,
partly in section, the form of tasimeter which Edison
took with him to Rawlins, Wyoming, in July, 1878, on the
expedition to observe the total eclipse of the sun.

The substance on whose expansion the working of the

Book of the day: