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

Part 15 out of 17

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instrument depends is a strip of some material extremely
sensitive to heat, such as vulcanite. shown at A, and firmly
clamped at B. Its lower end fits into a slot in a metal plate,
C, which in turn rests upon a carbon button. This latter
and the metal plate are connected in an electric circuit which
includes a battery and a sensitive galvanometer. A vulcanite
or other strip is easily affected by differences of
temperature, expanding and contracting by reason of the
minutest changes. Thus, an infinitesimal variation in its
length through expansion or contraction changes the press-
ure on the carbon and affects the resistance of the circuit
to a corresponding degree, thereby causing a deflection of
the galvanometer; a movement of the needle in one direction
denoting expansion, and in the other contraction. The
strip, A, is first put under a slight pressure, deflecting the
needle a few degrees from zero. Any subsequent expansion
or contraction of the strip may readily be noted by further
movements of the needle. In practice, and for measurements
of a very delicate nature, the tasimeter is inserted in
one arm of a Wheatstone bridge, as shown at A in the
diagram (Fig. 2). The galvanometer is shown at B in the
bridge wire, and at C, D, and E there are shown the resistances
in the other arms of the bridge, which are adjusted to
equal the resistance of the tasimeter circuit. The battery
is shown at F. This arrangement tends to obviate any misleading
deflections that might arise through changes in the battery.

The dial on the front of the instrument is intended to indicate
the exact amount of physical expansion or contraction
of the strip. This is ascertained by means of a micrometer
screw, S, which moves a needle, T, in front of the dial.
This screw engages with a second and similar screw which
is so arranged as to move the strip of vulcanite up or down.
After a galvanometer deflection has been obtained through
the expansion or contraction of the strip by reason of a
change of temperature, a similar deflection is obtained
mechanically by turning the screw, S, one way or the other.
This causes the vulcanite strip to press more or less upon
the carbon button, and thus produces the desired change
in the resistance of the circuit. When the galvanometer
shows the desired deflection, the needle, T, will indicate upon
the dial, in decimal fractions of an inch, the exact distance
through which the strip has been moved.

With such an instrument as the above, Edison demonstrated
the existence of heat in the corona at the above-
mentioned total eclipse of the sun, but exact determinations
could not be made at that time, because the tasimeter adjustment
was too delicate, and at the best the galvanometer
deflections were so marked that they could not be kept
within the limits of the
scale. The sensitiveness
of the instrument may
be easily comprehended
when it is stated that
the heat of the hand
thirty feet away from
the cone-like funnel of
the tasimeter will so
affect the galvanometer
as to cause the spot of
light to leave the scale.

This instrument can also be used to indicate minute changes of
moisture in the air by substituting a strip of gelatine in
place of the vulcanite. When so arranged a moistened
piece of paper held several feet away will cause a minute
expansion of the gelatine strip, which effects a pressure
on the carbon, and causes a variation in the circuit sufficient
to throw the spot of light from the galvanometer mirror off
the scale.

The tasimeter has been used to demonstrate heat from
remote stars (suns), such as Arcturus.



THE first patent that was ever granted on a device for
permanently recording the human voice and other sounds, and
for reproducing the same audibly at any future time, was
United States Patent No. 200,251, issued to Thomas A.
Edison on February 19, 1878, the application having been
filed December 24, 1877. It is worthy of note that no references
whatever were cited against the application while
under examination in the Patent Office. This invention
therefore, marked the very beginning of an entirely new
art, which, with the new industries attendant upon its
development, has since grown to occupy a position of worldwide

That the invention was of a truly fundamental character
is also evident from the fact that although all "talking-
machines" of to-day differ very widely in refinement from
the first crude but successful phonograph of Edison, their
performance is absolutely dependent upon the employment
of the principles stated by him in his Patent No. 200,251.
Quoting from the specification attached to this patent, we
find that Edison said:

"The invention consists in arranging a plate, diaphragm
or other flexible body capable of being vibrated by the
human voice or other sounds, in conjunction with a material
capable of registering the movements of such vibrating
body by embossing or indenting or altering such material,
in such a manner that such register marks will be sufficient to
cause a second vibrating plate or body to be set in motion
by them, and thus reproduce the motions of the first vibrating

It will be at once obvious that these words describe perfectly
the basic principle of every modern phonograph or
other talking-machine, irrespective of its manufacture or
trade name.

Edison's first model of the phonograph is shown in the
following illustration.

It consisted of a metallic cylinder having a helical indenting
groove cut upon it from end to end. This cylinder was
mounted on a shaft supported on two standards. This
shaft at one end was fitted with a handle, by means of which
the cylinder was rotated. There were two diaphragms, one
on each side of the cylinder, one being for recording and the
other for reproducing speech or other sounds. Each diaphragm
had attached to it a needle. By means of the needle
attached to the recording diaphragm, indentations were
made in a sheet of tin-foil stretched over the peripheral sur-
face of the cylinder when the diaphragm was vibrated by
reason of speech or other sounds. The needle on the other
diaphragm subsequently followed these indentations, thus
reproducing the original sounds.

Crude as this first model appears in comparison with
machines of later development and refinement, it embodied
their fundamental essentials, and was in fact a complete,
practical phonograph from the first moment of its operation.

The next step toward the evolution of the improved phono-
graph of to-day was another form of tin-foil machine, as seen
in the illustration.

It will be noted that this was merely an elaborated form
of the first model, and embodied several mechanical
modifications, among which was the employment of only one
diaphragm for recording and reproducing. Such was the
general type of phonograph used for exhibition purposes in
America and other countries in the three or four years
immediately succeeding the date of this invention.

In operating the machine the recording diaphragm was
advanced nearly to the cylinder, so that as the diaphragm
was vibrated by the voice the needle would prick or indent a
wave-like record in the tin-foil that was on the cylinder. The
cylinder was constantly turned during the recording, and
in turning, was simultaneously moved forward. Thus the
record would be formed on the tin-foil in a continuous spiral
line. To reproduce this record it was only necessary to
again start at the beginning and cause the needle to retrace
its path in the spiral line. The needle, in passing rapidly
in contact with the recorded waves, was vibrated up and
down, causing corresponding vibrations of the diaphragm.
In this way sound-waves similar to those caused by the
original sounds would be set up in the air, thus reproducing
the original speech.

The modern phonograph operates in a precisely similar
way, the only difference being in details of refinement. In-
stead of tin-foil, a wax cylinder is employed, the record being
cut thereon by a cutting-tool attached to a diaphragm, while
the reproduction is effected by means of a blunt stylus
similarly attached.

The cutting-tool and stylus are devices made of sapphire,
a gem next in hardness to a diamond, and they have to be
cut and formed to an exact nicety by means of diamond dust,
most of the work being performed under high-powered
microscopes. The minute proportions of these devices will be
apparent by a glance at the accompanying illustrations, in
which the object on the left represents a
common pin, and the objects on the right
the cutting-tool and reproducing stylus,
all actual sizes.

In the next illustration (Fig. 4) there is
shown in the upper sketch, greatly magnified,
the cutting or recording tool in the
act of forming the record, being vibrated
rapidly by the diaphragm; and in the
lower sketch, similarly enlarged, a representation
of the stylus travelling over the
record thus made, in the act of effecting
a reproduction.

From the late summer of 1878 and to the fall of 1887
Edison was intensely busy on the electric light, electric railway,
and other problems, and virtually gave no attention to
the phonograph. Hence, just
prior to the latter-named period
the instrument was still
in its tin-foil age; but he
then began to devote serious
attention to the development
of an improved type that
should be of greater commercial
importance. The practical
results are too well known
to call for further comment.
That his efforts were not limited
in extent may be inferred
from the fact that since the fall of 1887 to the present
writing he has been granted in the United States one hun-
dred and four patents relating to the phonograph and its

Interesting as the numerous inventions are, it would be
a work of supererogation to digest all these patents in the
present pages, as they represent not only the inception but
also the gradual development and growth of the wax-record
type of phonograph from its infancy to the present perfected
machine and records now so widely known all over the world.
From among these many inventions, however, we will select
two or three as examples of ingenuity and importance in their
bearing upon present perfection of results

One of the difficulties of reproduction for many years was
the trouble experienced in keeping the stylus in perfect en-
gagement with the wave-like record, so that every minute
vibration would be reproduced. It should be remembered
that the deepest cut of the recording tool is only about one-
third the thickness of tissue-paper. Hence, it will be quite
apparent that the slightest inequality in the surface of the
wax would be sufficient to cause false vibration, and thus
give rise to distorted effects in such music or other sounds
as were being reproduced. To remedy this, Edison added
an attachment which is called a "floating weight," and is
shown at A in the illustration above.

The function of the floating weight is to automatically keep
the stylus in close engagement with the record, thus insuring
accuracy of reproduction. The weight presses the stylus to
its work, but because of its mass it cannot respond to the
extremely rapid vibrations of the stylus. They are therefore
communicated to the diaphragm.

Some of Edison's most remarkable inventions are revealed
in a number of interesting patents relating to the duplication
of phonograph records. It would be obviously impossible,
from a commercial standpoint, to obtain a musical record
from a high-class artist and sell such an original to the public,
as its cost might be from one hundred to several thousand
dollars. Consequently, it is necessary to provide some way
by which duplicates may be made cheaply enough to permit
their purchase by the public at a reasonable price.

The making of a perfect original musical or other record
is a matter of no small difficulty, as it requires special technical
knowledge and skill gathered from many years of actual
experience; but in the exact copying, or duplication, of such
a record, with its many millions of microscopic waves and
sub-waves, the difficulties are enormously increased. The
duplicates must be microscopically identical with the original,
they must be free from false vibrations or other defects,
although both original and duplicates are of such easily
defacable material as wax; and the process must be cheap and
commercial not a scientific laboratory possibility.

For making duplicates it was obviously necessary to first
secure a mold carrying the record in negative or reversed
form. From this could be molded, or cast, positive copies
which would be identical with the original. While the art
of electroplating would naturally suggest itself as the means
of making such a mold, an apparently insurmountable
obstacle appeared on the very threshold. Wax, being a non-
conductor, cannot be electroplated unless a conducting surface
be first applied. The coatings ordinarily used in electro-
deposition were entirely out of the question on account of
coarseness, the deepest waves of the record being less than
one-thousandth of an inch in depth, and many of them probably
ten to one hundred times as shallow. Edison finally
decided to apply a preliminary metallic coating of infinitesimal
thinness, and accomplished this object by a remarkable
process known as the vacuous deposit. With this he ap-
plied to the original record a film of gold probably no thicker
than one three-hundred-thousandth of an inch, or several
hundred times less than the depth of an average wave.
Three hundred such layers placed one on top of the other
would make a sheet no thicker than tissue-paper.

The process consists in placing in a vacuum two leaves,
or electrodes, of gold, and between them the original record.
A constant discharge of electricity of high tension between
the electrodes is effected by means of an induction-coil. The
metal is vaporized by this discharge, and is carried by it
directly toward and deposited upon the original record, thus
forming the minute film of gold above mentioned. The
record is constantly rotated until its entire surface is coated.
A sectional diagram of the apparatus (Fig. 6.) will aid to a
clearer understanding of this ingenious process.

After the gold film is formed in the manner described
above, a heavy backing of baser metal is electroplated upon
it, thus forming a substantial mold, from which the original
record is extracted by breakage or shrinkage.

Duplicate records in any quantity may now be made from
this mold by surrounding it with a cold-water jacket and
dipping it in a molten wax-like material. This congeals on
the record surface just as melted butter would collect on a
cold knife, and when the mold is removed the surplus wax
falls out, leaving a heavy deposit of the material which forms
the duplicate record. Numerous ingenious inventions have
been made by Edison providing for a variety of rapid and
economical methods of duplication, including methods of
shrinking a newly made copy to facilitate its quick removal
from the mold; methods of reaming, of forming ribs on the
interior, and for many other important and essential details,
which limits of space will not permit of elaboration. Those
mentioned above are but fair examples of the persistent and
effective work he has done to bring the phonograph to its
present state of perfection.

In perusing Chapter X of the foregoing narrative, the
reader undoubtedly noted Edison's clear apprehension of
the practical uses of the phonograph, as evidenced by his
prophetic utterances in the article written by him for the
North American Review in June, 1878. In view of the
crudity of the instrument at that time, it must be acknowl-
edged that Edison's foresight, as vindicated by later events
was most remarkable. No less remarkable was his intensely
practical grasp of mechanical possibilities of future types of
the machine, for we find in one of his early English patents
(No. 1644 of 1878) the disk form of phonograph which, some
ten to fifteen years later, was supposed to be a new development
in the art. This disk form was also covered by Edison's
application for a United States patent, filed in 1879.
This application met with some merely minor technical objections
in the Patent Office, and seems to have passed into
the "abandoned" class for want of prosecution, probably
because of being overlooked in the tremendous pressure
arising from his development of his electric-lighting system.



ALTHOUGH Edison's contributions to human comfort and
progress are extensive in number and extraordinarily vast
and comprehensive in scope and variety, the universal verdict
of the world points to his incandescent lamp and system
of distribution of electrical current as the central and crowning
achievements of his life up to this time. This view
would seem entirely justifiable when we consider the wonderful
changes in the conditions of modern life that have
been brought about by the wide-spread employment of these
inventions, and the gigantic industries that have grown up
and been nourished by their world-wide application. That
he was in this instance a true pioneer and creator is
evident as we consider the subject, for the United States
Patent No. 223,898, issued to Edison on January 27, 1880,
for an incandescent lamp, was of such fundamental character
that it opened up an entirely new and tremendously important
art--the art of incandescent electric lighting. This
statement cannot be successfully controverted, for it has
been abundantly verified after many years of costly litigation.
If further proof were desired, it is only necessary to
point to the fact that, after thirty years of most strenuous
and practical application in the art by the keenest intellects
of the world, every incandescent lamp that has ever since
been made, including those of modern days, is still dependent
upon the employment of the essentials disclosed in the
above-named patent--namely, a filament of high resistance
enclosed in a sealed glass globe exhausted of air, with conducting
wires passing through the glass.

An incandescent lamp is such a simple-appearing article--
merely a filament sealed into a glass globe--that its intrinsic
relation to the art of electric lighting is far from being ap-
parent at sight. To the lay mind it would seem that this
must have been THE obvious device to make in order to obtain
electric light by incandescence of carbon or other material.
But the reader has already learned from the preceding
narrative that prior to its invention by Edison such a device
was NOT obvious, even to the most highly trained experts of
the world at that period; indeed, it was so far from being
obvious that, for some time after he had completed practical
lamps and was actually lighting them up twenty-four
hours a day, such a device and such a result were declared
by these same experts to be an utter impossibility. For a
short while the world outside of Menlo Park held Edison's
claims in derision. His lamp was pronounced a fake, a
myth, possibly a momentary success magnified to the dignity
of a permanent device by an overenthusiastic inventor.

Such criticism, however, did not disturb Edison. He
KNEW that he had reached the goal. Long ago, by a close
process of reasoning, he had clearly seen that the only road
to it was through the path he had travelled, and which was
now embodied in the philosophy of his incandescent lamp--
namely, a filament, or carbon, of high resistance and small
radiating surface, sealed into a glass globe exhausted of air
to a high degree of vacuum. In originally committing himself
to this line of investigation he was well aware that he
was going in a direction diametrically opposite to that followed
by previous investigators. Their efforts had been confined
to low-resistance burners of large radiating surface for
their lamps, but he realized the utter futility of such devices.
The tremendous problems of heat and the prohibitive quantities
of copper that would be required for conductors for
such lamps would be absolutely out of the question in commercial

He was convinced from the first that the true solution of
the problem lay in a lamp which should have as its illuminating
body a strip of material which would offer such a resistance
to the flow of electric current that it could be raised
to a high temperature--incandescence--and be of such small
cross-section that it would radiate but little heat. At the
same time such a lamp must require a relatively small amount
of current, in order that comparatively small conductors
could be used, and its burner must be capable of withstand-
ing the necessarily high temperatures without disintegration.

It is interesting to note that these conceptions were in
Edison's mind at an early period of his investigations, when
the best expert opinion was that the subdivision of the electric
current was an ignis fatuus. Hence we quote the following
notes he made, November 15, 1878, in one of the
laboratory note-books:

"A given straight wire having 1 ohm resistance and certain
length is brought to a given degree of temperature by
given battery. If the same wire be coiled in such a manner
that but one-quarter of its surface radiates, its temperature
will be increased four times with the same battery, or, one-
quarter of this battery will bring it to the temperature of
straight wire. Or the same given battery will bring a wire
whose total resistance is 4 ohms to the same temperature as
straight wire.

"This was actually determined by trial.

"The amount of heat lost by a body is in proportion to
the radiating surface of that body. If one square inch of
platina be heated to 100 degrees it will fall to, say, zero in one second,
whereas, if it was at 200 degrees it would require two seconds.

"Hence, in the case of incandescent conductors, if the
radiating surface be twelve inches and the temperature on
each inch be 100, or 1200 for all, if it is so coiled or arranged
that there is but one-quarter, or three inches, of radiating
surface, then the temperature on each inch will be 400. If
reduced to three-quarters of an inch it will have on that three-
quarters of an inch 1600 degrees Fahr., notwithstanding the original
total amount was but 1200, because the radiation has been reduced
to three-quarters, or 75 units; hence, the effect of the
lessening of the radiation is to raise the temperature of each
remaining inch not radiating to 125 degrees. If the radiating surface
should be reduced to three-thirty-seconds of an inch, the
temperature would reach 6400 degrees Fahr. To carry out this law
to the best advantage in regard to platina, etc., then with a
given length of wire to quadruple the heat we must lessen the
radiating surface to one-quarter, and to do this in a spiral,
three-quarters must be within the spiral and one-quarter
outside for radiating; hence, a square wire or other means,
such as a spiral within a spiral, must be used. These results
account for the enormous temperature of the Electric Arc
with one horse-power; as, for instance, if one horse-power
will heat twelve inches of wire to 1000 degrees Fahr., and this is
concentrated to have one-quarter of the radiating surface,
it would reach a temperature of 4000 degrees or sufficient to melt it;
but, supposing it infusible, the further concentration to one-
eighth its surface, it would reach a temperature of 16,000 degrees,
and to one-thirty-second its surface, which would be about
the radiating surface of the Electric Arc, it would reach
64,000 degrees Fahr. Of course, when Light is radiated in great
quantities not quite these temperatures would be reached.

"Another curious law is this: It will require a greater
initial battery to bring an iron wire of the same size and
resistance to a given temperature than it will a platina wire
in proportion to their specific heats, and in the case of Carbon,
a piece of Carbon three inches long and one-eighth diameter,
with a resistance of 1 ohm, will require a greater battery
power to bring it to a given temperature than a cylinder
of thin platina foil of the same length, diameter, and resistance,
because the specific heat of Carbon is many times greater;
besides, if I am not mistaken, the radiation of a roughened
body for heat is greater than a polished one like platina."

Proceeding logically upon these lines of thought and
following them out through many ramifications, we have seen
how he at length made a filament of carbon of high resistance
and small radiating surface, and through a concurrent
investigation of the phenomena of high vacua and occluded
gases was able to produce a true incandescent lamp. Not
only was it a lamp as a mere article--a device to give light--
but it was also an integral part of his great and complete
system of lighting, to every part of which it bore a fixed and
definite ratio, and in relation to which it was the keystone
that held the structure firmly in place.

The work of Edison on incandescent lamps did not stop
at this fundamental invention, but extended through more
than eighteen years of a most intense portion of his busy
life. During that period he was granted one hundred and
forty-nine other patents on the lamp and its manufacture.
Although very many of these inventions were of the utmost
importance and value, we cannot attempt to offer a detailed
exposition of them in this necessarily brief article, but must
refer the reader, if interested, to the patents themselves, a
full list being given at the end of this Appendix.
The outline sketch will indicate the principal patents
covering the basic features of the lamp.

The litigation on the Edison lamp patents was one of the
most determined and stubbornly fought contests in the
history of modern jurisprudence. Vast interests were at
stake. All of the technical, expert, and professional skill
and knowledge that money could procure or experience devise
were availed of in the bitter fights that raged in the
courts for many years. And although the Edison interests
had spent from first to last nearly $2,000,000, and had only
about three years left in the life of the fundamental patent,
Edison was thoroughly sustained as to priority by the decisions
in the various suits. We shall offer a few brief extracts
from some of these decisions.

In a suit against the United States Electric Lighting Company,
United States Circuit Court for the Southern District
of New York, July 14, 1891, Judge Wallace said, in his opinion:
"The futility of hoping to maintain a burner in vacuo
with any permanency had discouraged prior inventors, and
Mr. Edison is entitled to the credit of obviating the mechanical
difficulties which disheartened them.... He was
the first to make a carbon of materials, and by a process
which was especially designed to impart high specific resistance
to it; the first to make a carbon in the special form
for the special purpose of imparting to it high total resistance;
and the first to combine such a burner with the necessary adjuncts
of lamp construction to prevent its disintegration and
give it sufficiently long life. By doing these things he made
a lamp which was practically operative and successful, the
embryo of the best lamps now in commercial use, and but
for which the subdivision of the electric light by incandescence
would still be nothing but the ignis fatuus which it
was proclaimed to be in 1879 by some of the reamed experts
who are now witnesses to belittle his achievement and show
that it did not rise to the dignity of an invention.... It is
impossible to resist the conclusion that the invention of the
slender thread of carbon as a substitute for the burners
previously employed opened the path to the practical subdivision
of the electric light."

An appeal was taken in the above suit to the United States
Circuit Court of Appeals, and on October 4, 1892, the decree
of the lower court was affirmed. The judges (Lacombe and
Shipman), in a long opinion reviewed the facts and the art,
and said, inter alia: "Edison's invention was practically
made when he ascertained the theretofore unknown fact that
carbon would stand high temperature, even when very at-
tenuated, if operated in a high vacuum, without the phenomenon
of disintegration. This fact he utilized by the means
which he has described, a lamp having a filamentary carbon
burner in a nearly perfect vacuum."

In a suit against the Boston Incandescent Lamp Company
et al., in the United States Circuit Court for the District
of Massachusetts, decided in favor of Edison on June 11,
1894, Judge Colt, in his opinion, said, among other things:
"Edison made an important invention; he produced the
first practical incandescent electric lamp; the patent is a
pioneer in the sense of the patent law; it may be said that
his invention created the art of incandescent electric lighting."

Opinions of other courts, similar in tenor to the foregoing,
might be cited, but it would be merely in the nature of
reiteration. The above are sufficient to illustrate the direct
clearness of judicial decision on Edison's position as the
founder of the art of electric lighting by incandescence.


AT the present writing, when, after the phenomenally
rapid electrical development of thirty years, we find on the
market a great variety of modern forms of efficient current
generators advertised under the names of different inventors
(none, however, bearing the name of Edison), a young electrical
engineer of the present generation might well inquire
whether the great inventor had ever contributed anything
to the art beyond a mere TYPE of machine formerly made and
bearing his name, but not now marketed except second hand.

For adequate information he might search in vain the
books usually regarded as authorities on the subject of
dynamo-electric machinery, for with slight exceptions there
has been a singular unanimity in the omission of writers to
give Edison credit for his great and basic contributions to
heavy-current technics, although they have been universally
acknowledged by scientific and practical men to have laid
the foundation for the efficiency of, and to be embodied in
all modern generators of current.

It might naturally be expected that the essential facts of
Edison's work would appear on the face of his numerous
patents on dynamo-electric machinery, but such is not
necessarily the case, unless they are carefully studied in the
light of the state of the art as it existed at the time. While
some of these patents (especially the earlier ones) cover
specific devices embodying fundamental principles that not
only survive to the present day, but actually lie at the foundation
of the art as it now exists, there is no revelation
therein of Edison's preceding studies of magnets, which extended
over many years, nor of his later systematic investigations
and deductions.

Dynamo-electric machines of a primitive kind had been
invented and were in use to a very limited extent for arc
lighting and electroplating for some years prior to the summer
of 1819, when Edison, with an embryonic lighting SYSTEM
in mind, cast about for a type of machine technically and
commercially suitable for the successful carrying out of his
plans. He found absolutely none. On the contrary, all of
the few types then obtainable were uneconomical, indeed
wasteful, in regard to efficiency. The art, if indeed there
can be said to have been an art at that time, was in chaotic
confusion, and only because of Edison's many years' study
of the magnet was he enabled to conclude that insufficiency
in quantity of iron in the magnets of such machines, together
with poor surface contacts, rendered the cost of magnetization
abnormally high. The heating of solid armatures, the
only kind then known, and poor insulation in the commutators,
also gave rise to serious losses. But perhaps the most
serious drawback lay in the high-resistance armature, based
upon the highest scientific dictum of the time that in order
to obtain the maximum amount of work from a machine,
the internal resistance of the armature must equal the resistance
of the exterior circuit, although the application of
this principle entailed the useless expenditure of at least
50 per cent. of the applied energy.

It seems almost incredible that only a little over thirty
years ago the sum of scientific knowledge in regard to dynamo-
electric machines was so meagre that the experts of the
period should settle upon such a dictum as this, but such
was the fact, as will presently appear. Mechanical generators
of electricity were comparatively new at that time;
their theory and practice were very imperfectly understood;
indeed, it is quite within the bounds of truth to say that the
correct principles were befogged by reason of the lack of
practical knowledge of their actual use. Electricians and
scientists of the period had been accustomed for many years
past to look to the chemical battery as the source from
which to obtain electrical energy; and in the practical
application of such energy to telegraphy and kindred uses,
much thought and ingenuity had been expended in studying
combinations of connecting such cells so as to get the
best results. In the text-books of the period it was stated
as a settled principle that, in order to obtain the maximum
work out of a set of batteries, the internal resistance must
approximately equal the resistance of the exterior circuit.
This principle and its application in practice were quite correct
as regards chemical batteries, but not as regards dynamo
machines. Both were generators of electrical current, but
so different in construction and operation, that rules applicable
to the practical use of the one did not apply with
proper commercial efficiency to the other. At the period
under consideration, which may be said to have been just
before dawn of the day of electric light, the philosophy of
the dynamo was seen only in mysterious, hazy outlines--
just emerging from the darkness of departing night. Perhaps
it is not surprising, then, that the dynamo was loosely
regarded by electricians as the practical equivalent of a
chemical battery; that many of the characteristics of performance
of the chemical cell were also attributed to it, and
that if the maximum work could be gotten out of a set of
batteries when the internal and external resistances were
equal (and this was commercially the best thing to do), so
must it be also with a dynamo.

It was by no miracle that Edison was far and away ahead
of his time when he undertook to improve the dynamo. He
was possessed of absolute KNOWLEDGE far beyond that of his
contemporaries. This he ad acquired by the hardest kind
of work and incessant experiment with magnets of all kinds
during several years preceding, particularly in connection
with his study of automatic telegraphy. His knowledge of
magnets was tremendous. He had studied and experimented
with electromagnets in enormous variety, and
knew their peculiarities in charge and discharge, lag, self-
induction, static effects, condenser effects, and the various
other phenomena connected therewith. He had also made
collateral studies of iron, steel, and copper, insulation, winding,
etc. Hence, by reason of this extensive work and knowledge,
Edison was naturally in a position to realize the utter
commercial impossibility of the then best dynamo machine
in existence, which had an efficiency of only about 40 per
cent., and was constructed on the "cut-and-try" principle.

He was also naturally in a position to assume the task he
set out to accomplish, of undertaking to plan and-build an
improved type of machine that should be commercial in hav-
ing an efficiency of at least 90 per cent. Truly a prodigious
undertaking in those dark days, when from the standpoint
of Edison's large experience the most practical and correct
electrical treatise was contained in the Encyclopaedia Britannica,
and in a German publication which Mr. Upton had
brought with him after he had finished his studies with the
illustrious Helmholtz. It was at this period that Mr. Upton
commenced his association with Edison, bringing to the great
work the very latest scientific views and the assistance of
the higher mathematics, to which he had devoted his attention
for several years previously.

As some account of Edison's investigations in this connection
has already been given in Chapter XII of the narrative,
we shall not enlarge upon them here, but quote from
An Historical Review, by Charles L. Clarke, Laboratory
Assistant at Menlo Park, 1880-81; Chief Engineer of the
Edison Electric Light Company, 1881-84:

"In June, 1879, was published the account of the Edison
dynamo-electric machine that survived in the art. This
machine went into extensive commercial use, and was notable
for its very massive and powerful field-magnets and
armature of extremely low resistance as compared with the
combined external resistance of the supply-mains and lamps.
By means of the large masses of iron in the field-magnets,
and closely fitted joints between the several parts thereof,
the magnetic resistance (reluctance) of the iron parts of the
magnetic circuit was reduced to a minimum, and the required
magnetization effected with the maximum economy.
At the same time Mr. Edison announced the commercial
necessity of having the armature of the dynamo of low resistance,
as compared with the external resistance, in order
that a large percentage of the electrical energy developed
should be utilized in the lamps, and only a small percentage
lost in the armature, albeit this procedure reduced the total
generating capacity of the machine. He also proposed to
make the resistance of the supply-mains small, as compared
with the combined resistance of the lamps in multiple arc,
in order to still further increase the percentage of energy
utilized in the lamps. And likewise to this end the combined
resistance of the generator armatures in multiple arc
was kept relatively small by adjusting the number of generators
operating in multiple at any time to the number of lamps
then in use. The field-magnet circuits of the dynamos were
connected in multiple with a separate energizing source;
and the field-current; and strength of field, were regulated
to maintain the required amount of electromotive force
upon the supply-mains under all conditions of load from the
maximum to the minimum number of lamps in use, and to
keep the electromotive force of all machines alike."

Among the earliest of Edison's dynamo experiments were
those relating to the core of the armature. He realized at
once that the heat generated in a solid core was a prolific
source of loss. He experimented with bundles of iron wires
variously insulated, also with sheet-iron rolled cylindrically
and covered with iron wire wound concentrically. These
experiments and many others were tried in a great variety
of ways, until, as the result of all this work, Edison arrived
at the principle which has remained in the art to this day.
He split up the iron core of the armature into thin laminations,
separated by paper, thus practically suppressing Foucault
currents therein and resulting heating effect. It was
in his machine also that mica was used for the first time as
an insulating medium in a commutator.[27]

[27] The commercial manufacture of built-up sheets of mica for electrical
purposes was first established at the Edison Machine Works, Goerck Street,
New York, in 1881.

Elementary as these principles will appear to the modern
student or engineer, they were denounced as nothing short
of absurdity at the time of their promulgation--especially
so with regard to Edison's proposal to upset the then settled
dictum that the armature resistance should be equal to the
external resistance. His proposition was derided in the
technical press of the period, both at home and abroad. As
public opinion can be best illustrated by actual quotation,
we shall present a characteristic instance.

In the Scientific American of October 18, 1879, there appeared
an illustrated article by Mr. Upton on Edison's
dynamo machine, in which Edison's views and claims were
set forth. A subsequent issue contained a somewhat acri-
monious letter of criticism by a well-known maker of dynamo
machines. At the risk of being lengthy, we must quote
nearly all this letter: "I can scarcely conceive it as possible
that the article on the above subject "(Edison's Electric
Generator)" in last week's Scientific American could have
been written from statements derived from Mr. Edison himself,
inasmuch as so many of the advantages claimed for
the machine described and statements of the results obtained
are so manifestly absurd as to indicate on the part of both
writer and prompter a positive want of knowledge of the
electric circuit and the principles governing the construction
and operation of electric machines.

"It is not my intention to criticise the design or construction
of the machine (not because they are not open to
criticism), as I am now and have been for many years engaged
in the manufacture of electric machines, but rather
to call attention to the impossibility of obtaining the described
results without destroying the doctrine of the conservation
and correlation of forces.

. . . . .

"It is stated that `the internal resistance of the armature'
of this machine `is only 1/2 ohm.' On this fact and the
disproportion between this resistance and that of the external
circuit, the theory of the alleged efficiency of the
machine is stated to be based, for we are informed that,
`while this generator in general principle is the same as in
the best well-known forms, still there is an all-important
difference, which is that it will convert and deliver for useful
work nearly double the number of foot-pounds that any
other machine will under like conditions.' " The writer of
this critical letter then proceeds to quote Mr. Upton's statement
of this efficiency: "`Now the energy converted is distributed
over the whole resistance, hence if the resistance of
the machine be represented by 1 and the exterior circuit by
9, then of the total energy converted nine-tenths will be
useful, as it is outside of the machine, and one-tenth is lost
in the resistance of the machine.'"

After this the critic goes on to say:

"How any one acquainted with the laws of the electric
circuit can make such statements is what I cannot understand.
The statement last quoted is mathematically absurd.
It implies either that the machine is CAPABLE OF INCREASING
EXPENDITURE OF POWER, or that external resistance is
NOT resistance to the current induced in the Edison machine.

"Does Mr. Edison, or any one for him, mean to say that
r/n enables him to obtain nE, and that C IS NOT = E / (r/n + R)?
If so
Mr. Edison has discovered something MORE than perpetual
motion, and Mr. Keely had better retire from the field.

"Further on the writer (Mr. Upton) gives us another example
of this mode of reasoning when, emboldened and
satisfied with the absurd theory above exposed, he endeavors
to prove the cause of the inefficiency of the Siemens and
other machines. Couldn't the writer of the article see that
since C = E/(r + R) that by R/n or by making R = r, the machine
would, according to his theory, have returned more useful
current to the circuit than could be due to the power employed
(and in the ratio indicated), so that there would
actually be a creation of force!
. . . . . . .

"In conclusion allow me to say that if Mr Edison thinks
he has accomplished so much by the REDUCTION OF THE INTERNAL
RESISTANCE of his machine, that he has much more to do in
this direction before his machine will equal IN THIS RESPECT
others already in the market."

Another participant in the controversy on Edison's generator
was a scientific gentleman, who in a long article published
in the Scientific American, in November, 1879, gravely
undertook to instruct Edison in the A B C of electrical
principles, and then proceeded to demonstrate mathematically
critic concludes with a gentle rebuke to the inventor for ill-
timed jesting, and a suggestion to furnish AUTHENTIC information!

In the light of facts, as they were and are, this article is
so full of humor that we shall indulge in a few quotations
It commences in A B C fashion as follows: "Electric machines
convert mechanical into electrical energy.... The
ratio of yield to consumption is the expression of the efficiency
of the machine.... How many foot-pounds of elec-
tricity can be got out of 100 foot-pounds of mechanical
energy? Certainly not more than 100: certainly less....
The facts and laws of physics, with the assistance of mathematical
logic, never fail to furnish precious answers to
such questions."

The would-be critic then goes on to tabulate tests of certain
other dynamo machines by a committee of the Franklin
Institute in 1879, the results of which showed that these
machines returned about 50 per cent. of the applied mechanical
energy, ingenuously remarking: "Why is it that
when we have produced the electricity, half of it must slip
away? Some persons will be content if they are told simply
that it is a way which electricity has of behaving. But there
is a satisfactory rational explanation which I believe can be
made plain to persons of ordinary intelligence. It ought to
be known to all those who are making or using machines.
I am grieved to observe that many persons who talk and
write glibly about electricity do not understand it; some even
ignore or deny the fact to be explained."

Here follows HIS explanation, after which he goes on to
say: "At this point plausibly comes in a suggestion that the
internal part of the circuit be made very small and the external
part very large. Why not (say) make the internal
part 1 and the external 9, thus saving nine-tenths and losing
only one-tenth? Unfortunately, the suggestion is not practical;
a fallacy is concealed in it."

He then goes on to prove his case mathematically, to his
own satisfaction, following it sadly by condoling with and
a warning to Edison: "But about Edison's electric generator!
. . . No one capable of making the improvements in the
telegraph and telephone, for which we are indebted to Mr.
Edison, could be other than an accomplished electrician.
His reputation as a scientist, indeed, is smirched by the newspaper
exaggerations, and no doubt he will be more careful
in future. But there is a danger nearer home, indeed, among
his own friends and in his very household.

". . . The writer of page 242" (the original article) "is
probably a friend of Mr. Edison, but possibly, alas! a wicked
partner. Why does he say such things as these? `Mr. Edison
claims that he realizes 90 per cent. of the power applied
to this machine in external work.' . . . Perhaps the writer
is a humorist, and had in his mind Colonel Sellers, etc.,
which he could not keep out of a serious discussion; but
such jests are not good.

"Mr. Edison has built a very interesting machine, and he
has the opportunity of making a valuable contribution to
the electrical arts by furnishing authentic accounts of its

The foregoing extracts are unavoidably lengthy, but,
viewed in the light of facts, serve to illustrate most clearly
that Edison's conceptions and work were far and away ahead
of the comprehension of his contemporaries in the art, and
that his achievements in the line of efficient dynamo design
and construction were indeed truly fundamental and revolutionary
in character. Much more of similar nature to the
above could be quoted from other articles published elsewhere,
but the foregoing will serve as instances generally
representing all. In the controversy which appeared in the
columns of the Scientific American, Mr. Upton, Edison's
mathematician, took up the question on his side, and answered
the critics by further elucidations of the principles
on which Edison had founded such remarkable and radical
improvements in the art. The type of Edison's first dynamo-
electric machine, the description of which gave rise to the
above controversy, is shown in Fig. 1.

Any account of Edison's work on the dynamo would be
incomplete did it omit to relate his conception and construction
of the great direct-connected steam-driven generator
that was the prototype of the colossal units which are
used throughout the world to-day.

In the demonstrating plant installed and operated by him
at Menlo Park in 1880 ten dynamos of eight horse-power
each were driven by a slow-speed engine through a complicated
system of counter-shafting, and, to quote from Mr.
Clarke's Historical Review, "it was found that a considerable
percentage of the power of the engine was necessarily wasted
in friction by this method of driving, and to prevent this
waste and thus increase the economy of his system, Mr. Edison
conceived the idea of substituting a single large dynamo
for the several small dynamos, and directly coupling it with
the driving engine, and at the same time preserve the requisite
high armature speed by using an engine of the high-
speed type. He also expected to realize still further gains
in economy from the use of a large dynamo in place of several
small machines by a more than correspondingly lower
armature resistance, less energy for magnetizing the field,
and for other minor reasons. To the same end, he intended
to supply steam to the engine under a much higher boiler
pressure than was customary in stationary-engine driving
at that time."

The construction of the first one of these large machines
was commenced late in the year 1880. Early in 1881 it was
completed and tested, but some radical defects in armature
construction were developed, and it was also demonstrated
that a rate of engine speed too high for continuously safe
and economical operation had been chosen. The machine
was laid aside. An accurate illustration of this machine, as
it stood in the engine-room at Menlo Park, is given in Van
Nostrand's Engineering Magazine, Vol. XXV, opposite page
439, and a brief description is given on page 450.

With the experience thus gained, Edison began, in the
spring of 1881, at the Edison Machine Works, Goerck Street,
New York City, the construction of the first successful machine
of this type. This was the great machine known as
"Jumbo No. 1," which is referred to in the narrative as having
been exhibited at the Paris International Electrical Exposition,
where it was regarded as the wonder of the electrical
world. An intimation of some of the tremendous difficulties
encountered in the construction of this machine has already
been given in preceding pages, hence we shall not now enlarge
on the subject, except to note in passing that the terribly
destructive effects of the spark of self-induction and
the arcing following it were first manifested in this powerful
machine, but were finally overcome by Edison after a strenuous
application of his powers to the solution of the problem.

It may be of interest, however, to mention some of its
dimensions and electrical characteristics, quoting again from
Mr. Clarke: "The field-magnet had eight solid cylindrical
cores, 8 inches in diameter and 57 inches long, upon each of
which was wound an exciting-coil of 3.2 ohms resistance,
consisting of 2184 turns of No. 10 B. W. G. insulated copper
wire, disposed in six layers. The laminated iron core of the
armature, formed of thin iron disks, was 33 3/4 inches long,
and had an internal diameter of 12 1/2 inches, and an external
diameter of 26 7/16 inches. It was mounted on a 6-inch shaft.
The field-poles were 33 3/4 inches long, and 27 1/2 inches inside
diameter The armature winding consisted of 146 copper
bars on the face of the core, connected into a closed-coil
winding by means of 73 copper disks at each end of the core.
The cross-sectional area of each bar was 0.2 square inch
their average length was 42.7 inches, and the copper end-
disks were 0.065 inch thick. The commutator had 73 sec-
tions. The armature resistance was 0.0092 ohm,[28] of which
0.0055 ohm was in the armature bars and 0.0037 ohm in the
end-disks." An illustration of the next latest type of this
machine is presented in Fig. 2.

[28] Had Edison in Upton's Scientific American article in 1879 proposed
such an exceedingly low armature resistance for this immense generator
(although its ratio was proportionate to the original machine),
his critics might probably have been sufficiently indignant
as to be unable to express themselves coherently.

The student may find it interesting to look up Edison's
United States Patents Nos. 242,898, 263,133, 263,146, and
246,647, bearing upon the construction of the "Jumbo";
also illustrated articles in the technical journals of the time,
among which may be mentioned: Scientific American, Vol.
XLV, page 367; Engineering, London, Vol. XXXII, pages
409 and 419, The Telegraphic Journal and Electrical Review,
London, Vol. IX, pages 431-433, 436-446; La Nature, Paris,
9th year, Part II, pages 408-409; Zeitschrift fur Angewandte
Elektricitaatslehre, Munich and Leipsic, Vol. IV, pages 4-14;
and Dredge's Electric Illumination, 1882, Vol. I, page 261.

The further development of these great machines later on,
and their extensive practical use, are well known and need
no further comment, except in passing it may be noted that
subsequent machines had each a capacity of 1200 lamps of
16 candle-power, and that the armature resistance was still
further reduced to 0.0039 ohm.

Edison's clear insight into the future, as illustrated by his
persistent advocacy of large direct-connected generating
units, is abundantly vindicated by present-day practice.
His Jumbo machines, of 175 horse-power, so enormous for
their time, have served as prototypes, and have been succeeded
by generators which have constantly grown in size
and capacity until at this time (1910) it is not uncommon
to employ such generating units of a capacity of 14,000 kilowatts,
or about 18,666 horse-power.

We have not entered into specific descriptions of the
many other forms of dynamo machines invented by Edison,
such as the multipolar, the disk dynamo, and the armature
with two windings, for sub-station distribution; indeed, it is
not possible within our limited space to present even a brief
digest of Edison's great and comprehensive work on the
dynamo-electric machine, as embodied in his extensive ex-
periments and in over one hundred patents granted to him.
We have, therefore, confined ourselves to the indication of
a few salient and basic features, leaving it to the interested
student to examine the patents and the technical literature
of the long period of time over which Edison's labors
were extended.

Although he has not given any attention to the subject
of generators for many years, an interesting instance of his
incisive method of overcoming minor difficulties occurred
while the present volumes were under preparation (1909).
Carbon for commutator brushes has been superseded by
graphite in some cases, the latter material being found much
more advantageous, electrically. Trouble developed, however,
for the reason that while carbon was hard and would
wear away the mica insulation simultaneously with the
copper, graphite, being softer, would wear away only the
copper, leaving ridges of mica and thus causing sparking
through unequal contact. At this point Edison was asked
to diagnose the trouble and provide a remedy. He suggested
the cutting out of the mica pieces almost to the bottom,
leaving the commutator bars separated by air-spaces.
This scheme was objected to on the ground that particles
of graphite would fill these air-spaces and cause a short-
circuit. His answer was that the air-spaces constituted the
value of his plan, as the particles of graphite falling into them
would be thrown out by the action of centrifugal force as the
commutator revolved. And thus it occurred as a matter of
fact, and the trouble was remedied. This idea was subsequently
adopted by a great manufacturer of generators.



TO quote from the preamble of the specifications of United
States Patent No. 264,642, issued to Thomas A. Edison
September 19, 1882: "This invention relates to a method
of equalizing the tension or `pressure' of the current through
an entire system of electric lighting or other translation of
electric force, preventing what is ordinarily known as a
`drop' in those portions of the system the more remote from
the central station...."

The problem which was solved by the Edison feeder
system was that relating to the equal distribution of current
on a large scale over extended areas, in order that a constant
and uniform electrical pressure could be maintained in every
part of the distribution area without prohibitory expenditure
for copper for mains and conductors.

This problem had a twofold aspect, although each side
was inseparably bound up in the other. On the one hand
it was obviously necessary in a lighting system that each
lamp should be of standard candle-power, and capable of
interchangeable use on any part of the system, giving the
same degree of illumination at every point, whether near to
or remote from the source of electrical energy. On the other
hand, this must be accomplished by means of a system of
conductors so devised and arranged that while they would
insure the equal pressure thus demanded, their mass and
consequent cost would not exceed the bounds of practical
and commercially economical investment.

The great importance of this invention can be better understood
and appreciated by a brief glance at the state of the
art in 1878-79, when Edison was conducting the final series
of investigations which culminated in his invention of the
incandescent lamp and SYSTEM of lighting. At this time, and
for some years previously, the scientific world had been working
on the "subdivision of the electric light," as it was then
termed. Some leading authorities pronounced it absolutely
impossible of achievement on any extended scale, while a
very few others, of more optimistic mind, could see no gleam
of light through the darkness, but confidently hoped for
future developments by such workers as Edison.

The earlier investigators, including those up to the period
above named, thought of the problem as involving the subdivision
of a FIXED UNIT of current, which, being sufficient to
cause illumination by one large lamp, might be divided into
a number of small units whose aggregate light would equal
the candle-power of this large lamp. It was found, however,
in their experiments that the contrary effect was produced,
for with every additional lamp introduced in the
circuit the total candle-power decreased instead of increasing.
If they were placed in series the light varied inversely as
the SQUARE of the number of lamps in circuit; while if they
were inserted in multiple arc, the light diminished as the
CUBE of the number in circuit.[29] The idea of maintaining a
constant potential and of PROPORTIONING THE CURRENT to the
number of lamps in circuit did not occur to most of these
early investigators as a feasible method of overcoming the
supposed difficulty.

[29] M. Fontaine, in his book on Electric Lighting (1877), showed that with
the current of a battery composed of sixteen elements, one lamp gave an
illumination equal to 54 burners; whereas two similar lamps, if introduced
in parallel or multiple arc, gave the light of only 6 1/2 burners in all;
three lamps of only 2 burners in all; four lamps of only 3/4 of one burner,
and five lamps of 1/4 of a burner.

It would also seem that although the general method of
placing experimental lamps in multiple arc was known at
this period, the idea of "drop" of electrical pressure was
imperfectly understood, if, indeed, realized at all, as a most
important item to be considered in attempting the solution
of the problem. As a matter of fact, the investigators preceding
Edison do not seem to have conceived the idea of a
"system" at all; hence it is not surprising to find them far
astray from the correct theory of subdivision of the electric
current. It may easily be believed that the term "subdivision"
was a misleading one to these early experimenters.
For a very short time Edison also was thus misled, but as
soon as he perceived that the problem was one involving the
MULTIPLICATION OF CURRENT UNITS, his broad conception of a
"system" was born.

Generally speaking, all conductors of electricity offer more
or less resistance to the passage of current through them
and in the technical terminology of electrical science the
word "drop" (when used in reference to a system of distribution)
is used to indicate a fall or loss of initial electrical
pressure arising from the resistance offered by the copper
conductors leading from the source of energy to the lamps.
The result of this resistance is to convert or translate a
portion of the electrical energy into another form--namely,
heat, which in the conductors is USELESS and wasteful and to
some extent inevitable in practice, but is to be avoided and
remedied as far as possible.

It is true that in an electric-lighting system there is also
a fall or loss of electrical pressure which occurs in overcoming
the much greater resistance of the filament in an
incandescent lamp. In this case there is also a translation
of the energy, but here it accomplishes a USEFUL purpose, as
the energy is converted into the form of light through the
incandescence of the filament. Such a conversion is called
"work" as distinguished from "drop," although a fall of
initial electrical pressure is involved in each case.

The percentage of "drop" varies according to the quantity
of copper used in conductors, both as to cross-section and
length. The smaller the cross-sectional area, the greater the
percentage of drop. The practical effect of this drop would
be a loss of illumination in the lamps as we go farther away
from the source of energy. This may be illustrated by a
simple diagram in which G is a generator, or source of energy,
furnishing current at a potential or electrical pressure of
110 volts; 1 and 2 are main conductors, from which 110-volt
lamps, L, are taken in derived circuits. It will be understood
that the circuits represented in Fig. 1 are theoretically
supposed to extend over a large area. The main conductors
are sufficiently large in cross-section to offer but little
resistance in those parts which are comparatively near the
generator, but as the current traverses their extended
length there is a gradual increase of resistance to overcome,
and consequently the drop increases, as shown by the figures.
The result of the drop in such a case would be that while the
two lamps, or groups, nearest the generator would be burning
at their proper degree of illumination, those beyond would
give lower and lower candle-power, successively, until the
last lamp, or group, would be giving only about two-thirds
the light of the first two. In other words, a very slight drop
in voltage means a disproportionately great loss in illumination.
Hence, by using a primitive system of distribution,
such as that shown by Fig. 1, the initial voltage would have
to be so high, in order to obtain the proper candle-power at
the end of the circuit, that the lamps nearest the generator
would be dangerously overheated. It might be suggested
as a solution of this problem that lamps of different voltages
could be used. But, as we are considering systems of extended
distribution employing vast numbers of lamps (as in
New York City, where millions are in use), it will be seen that
such a method would lead to inextricable confusion, and
therefore be absolutely out of the question. Inasmuch as
the percentage of drop decreases in proportion to the increased
cross-section of the conductors, the only feasible plan
would seem to be to increase their size to such dimensions
as to eliminate the drop altogether, beginning with conductors
of large cross-section and tapering off as necessary.
This would, indeed, obviate the trouble, but, on the other
hand, would give rise to a much more serious difficulty--
namely, the enormous outlay for copper; an outlay so great
as to be absolutely prohibitory in considering the electric
lighting of large districts, as now practiced.

Another diagram will probably make this more clear.
The reference figures are used as before, except that the
horizontal lines extending from square marked G represent
the main conductors. As each lamp requires and takes its
own proportion of the total current generated, it is obvious
that the size of the conductors to carry the current for a
number of lamps must be as large as the sum of ALL the
separate conductors which would be required to carry the
necessary amount of current to each lamp separately.
Hence, in a primitive multiple-arc system, it was found that
the system must have conductors of a size equal to the
aggregate of the individual conductors necessary for every
lamp. Such conductors might either be separate, as shown
above (Fig. 2), or be bunched together, or made into a solid
tapering conductor, as shown in the following figure:

The enormous mass of copper needed in such a system
can be better appreciated by a concrete example. Some
years ago Mr. W. J. Jenks made a comparative calculation
which showed that such a system of conductors (known as
the "Tree" system), to supply 8640 lamps in a territory
extending over so small an area as nine city blocks, would
require 803,250 pounds of copper, which at the then price of
25 cents per pound would cost $200,812.50!

Such, in brief, was the state of the art, generally speaking,
at the period above named (1878-79). As early in the art
as the latter end of the year 1878, Edison had developed his
ideas sufficiently to determine that the problem of electric
illumination by small units could be solved by using incandescent
lamps of high resistance and small radiating surface,
and by distributing currents of constant potential
thereto in multiple arc by means of a ramification of conductors,
starting from a central source and branching therefrom
in every direction. This was an equivalent of the
method illustrated in Fig. 3, known as the "Tree" system,
and was, in fact, the system used by Edison in the first and
famous exhibition of his electric light at Menlo Park around
the Christmas period of 1879. He realized, however, that
the enormous investment for copper would militate against
the commercial adoption of electric lighting on an extended
scale. His next inventive step covered the division of a large
city district into a number of small sub-stations supplying
current through an interconnected network of conductors, thus
reducing expenditure for copper to some extent, because each
distribution unit was small and limited the drop.

His next development was the radical advancement of the
state of the art to the feeder system, covered by the patent
now under discussion. This invention swept away the tree and
other systems, and at one bound brought into being the possibility
of effectively distributing large currents over extended
areas with a commercially reasonable investment for copper.

The fundamental principles of this invention were, first,
to sever entirely any direct connection of the main conductors
with the source of energy; and, second, to feed current
at a constant potential to central points in such main
conductors by means of other conductors, called "feeders,"
which were to be connected directly with the source of energy
at the central station. This idea will be made more clear by
reference to the following simple diagram, in which the same
letters are used as before, with additions:

In further elucidation of the diagram, it may be considered
that the mains are laid in the street along a city
block, more or less distant from the station, while the feeders
are connected at one end with the source of energy at the
station, their other extremities being connected to the mains
at central points of distribution. Of course, this system
was intended to be applied in every part of a district to be
supplied with current, separate sets of feeders running out
from the station to the various centres. The distribution
mains were to be of sufficiently large size that between their
most extreme points the loss would not be more than 3 volts.
Such a slight difference would not make an appreciable
variation in the candle-power of the lamps.

By the application of these principles, the inevitable but
useless loss, or "drop," required by economy might be incurred,
but was LOCALIZED IN THE FEEDERS, where it would not
affect the uniformity of illumination of the lamps in any of
the circuits, whether near to or remote from the station,
because any variations of loss in the feeders would not give
rise to similar fluctuations in any lamp circuit. The feeders
might be operated at any desired percentage of loss that
would realize economy in copper, so long as they delivered
current to the main conductors at the potential represented
by the average voltage of the lamps.

Thus the feeders could be made comparatively small in
cross-section. It will be at once appreciated that, inasmuch
as the mains required to be laid ONLY along the blocks to be
lighted, and were not required to be run all the way to the
central station (which might be half a mile or more away),
the saving of copper by Edison's feeder system was enormous.
Indeed, the comparative calculation of Mr. Jenks,
above referred to, shows that to operate the same number
of lights in the same extended area of territory, the feeder
system would require only 128,739 pounds of copper, which,
at the then price of 25 cents per pound, would cost only
$39,185, or A SAVING of $168,627.50 for copper in this very
small district of only nine blocks.

An additional illustration, appealing to the eye, is
presented in the following sketch, in which the comparative
masses of copper of the tree and feeder systems for carrying
the same current are shown side by side:



THIS invention is covered by United States Patent No.
274,290, issued to Edison on March 20, 1883. The object
of the invention was to provide for increased economy in the
quantity of copper employed for the main conductors in
electric light and power installations of considerable extent
at the same time preserving separate and independent control
of each lamp, motor, or other translating device, upon
any one of the various distribution circuits.

Immediately prior to this invention the highest state of
the art of electrical distribution was represented by Edison's
feeder system, which has already been described as a straight
parallel or multiple-arc system wherein economy of copper
was obtained by using separate sets of conductors--minus
load--feeding current at standard potential or electrical
pressure into the mains at centres of distribution.

It should be borne in mind that the incandescent lamp
which was accepted at the time as a standard (and has so
remained to the present day) was a lamp of 110 volts or
thereabouts. In using the word "standard," therefore, it
is intended that the same shall apply to lamps of about that
voltage, as well as to electrical circuits of the approximate
potential to operate them.

Briefly stated, the principle involved in the three-wire
system is to provide main circuits of double the standard
potential, so as to operate standard lamps, or other translating
devices, in multiple series of two to each series; and
for the purpose of securing independent, individual control
of each unit, to divide each main circuit into any desired
number of derived circuits of standard potential (properly
balanced) by means of a central compensating conductor
which would be normally neutral, but designed to carry any
minor excess of current that might flow by reason of any
temporary unbalancing of either side of the main circuit.

Reference to the following diagrams will elucidate this
principle more clearly than words alone can do. For the
purpose of increased lucidity we will first show a plain
multiple-series system.

In this diagram G<1S> and G<2S> represent two generators, each
producing current at a potential of 110 volts. By connect-
ing them in series this potential is doubled, thus providing
a main circuit (P and N) of 220 volts. The figures marked
L represent eight lamps of 110 volts each, in multiple series
of two, in four derived circuits. The arrows indicate the
flow of current. By this method each pair of lamps takes,
together, only the same quantity or volume of current
required by a single lamp in a simple multiple-arc system;
and, as the cross-section of a conductor depends upon the
quantity of current carried, such an arrangement as the
above would allow the use of conductors of only one-fourth
the cross-section that would be otherwise required. From
the standpoint of economy of investment such an arrangement
would be highly desirable, but considered commercially
it is impracticable because the principle of independent
control of each unit would be lost, as the turning out of a lamp
in any series would mean the extinguishment of its
companion also. By referring to the diagram it will be seen
that each series of two forms one continuous path between
the main conductors, and if this path be broken at any one
point current will immediately cease to flow in that particular

Edison, by his invention of the three-wire system, over-
came this difficulty entirely, and at the same time conserved
approximately, the saving of copper, as will be apparent
from the following illustration of that system, in its simplest

The reference figures are similar to those in the preceding
diagram, and all conditions are also alike except that a
central compensating, or balancing, conductor, PN, is here
introduced. This is technically termed the "neutral" wire,
and in the discharge of its functions lies the solution of the
problem of economical distribution. Theoretically, a three-
wire installation is evenly balanced by wiring for an equal
number of lamps on both sides. If all these lamps were
always lighted, burned, and extinguished simultaneously the
central conductor would, in fact, remain neutral, as there
would be no current passing through it, except from lamp
to lamp. In practice, however, no such perfect conditions
can obtain, hence the necessity of the provision for balancing
in order to maintain the principle of independent control of
each unit.

It will be apparent that the arrangement shown in Fig. 2
comprises practically two circuits combined in one system,
in which the central conductor, PN, in case of emergency,
serves in two capacities--namely, as negative to generator
G<1S> or as positive to generator G<2S>, although normally neutral.
There are two sides to the system, the positive side being
represented by the conductors P and PN, and the negative
side by the conductors PN and N. Each side, if considered
separately, has a potential of about 110 volts, yet the potential
of the two outside conductors, P and N, is 220 volts.
The lamps are 110 volts.

In practical use the operation of the system is as follows:
If all the lamps were lighted the current would flow along
P and through each pair of lamps to N, and so back to the
source of energy. In this case the balance is preserved and
the central wire remains neutral, as no return current flows
through it to the source of energy. But let us suppose that
one lamp on the positive side is extinguished. None of the
other lamps is affected thereby, but the system is immediately
thrown out of balance, and on the positive side there
is an excess of current to this extent which flows along or
through the central conductor and returns to the generator,
the central conductor thus becoming the negative of that
side of the system for the time being. If the lamp extinguished
had been one of those on the negative side of the
system results of a similar nature would obtain, except that
the central conductor would for the time being become the
positive of that side, and the excess of current would flow
through the negative, N, back to the source of energy. Thus
it will be seen that a three-wire system, considered as a
whole, is elastic in that it may operate as one when in balance
and as two when unbalanced, but in either event giving independent
control of each unit.

For simplicity of illustration a limited number of circuits,
shown in Fig. 2, has been employed. In practice, however,
where great numbers of lamps are in use (as, for instance,
in New York City, where about 7,000,000 lamps are operated
from various central stations), there is constantly occurring
more or less change in the balance of many circuits extending
over considerable distances, but of course there is a net
result which is always on one side of the system or the other
for the time being, and this is met by proper adjustment at
the appropriate generator in the station.

In order to make the explanation complete, there is presented
another diagram showing a three-wire system unbalanced:

The reference figures are used as before, but in this case
the vertical lines represent branches taken from the main
conductors into buildings or other spaces to be lighted, and
the loops between these branch wires represent lamps in
operation. It will be seen from this sketch that there are
ten lamps on the positive side and twelve on the negative
side. Hence, the net result is an excess of current equal
to that required by two lamps flowing through the central
or compensating conductor, which is now acting as positive
to generator G<2S> The arrows show the assumed direction of
flow of current throughout the system, and the small figures
at the arrow-heads the volume of that current expressed in
the number of lamps which it supplies.

The commercial value of this invention may be appreciated
from the fact that by the application of its principles
there is effected a saving of 62 1/2 per cent. of the amount of
copper over that which would be required for conductors
in any previously devised two-wire system carrying the same
load. This arises from the fact that by the doubling of
potential the two outside mains are reduced to one-quarter
the cross-section otherwise necessary. A saving of 75 per
cent. would thus be assured, but the addition of a third, or
compensating, conductor of the same cross-section as one
of the outside mains reduces the total saving to 62 1/2 per cent.

The three-wire system is in universal use throughout the
world at the present day.



AS narrated in Chapter XVIII, there were two electric
railroads installed by Edison at Menlo Park--one in 1880,
originally a third of a mile long, but subsequently increased
to about a mile in length, and the other in 1882, about three
miles long. As the 1880 road was built very soon after
Edison's notable improvements in dynamo machines, and as
the art of operating them to the best advantage was then being
developed, this early road was somewhat crude as compared
with the railroad of 1882; but both were practicable and
serviceable for the purpose of hauling passengers and freight.
The scope of the present article will be confined to a
description of the technical details of these two installations.

The illustration opposite page 454 of the preceding narrative
shows the first Edison locomotive and train of 1880 at
Menlo Park.

For the locomotive a four-wheel iron truck was used, and
upon it was mounted one of the long "Z" type 110-volt
Edison dynamos, with a capacity of 75 amperes, which was
to be used as a motor. This machine was laid on its side,
its armature being horizontal and located toward the front
of the locomotive.

We now quote from an article by Mr. E. W. Hammer,
published in the Electrical World, New York, June 10, 1899,
and afterward elaborated and reprinted in a volume entitled
Edisonia, compiled and published under the auspices of a
committee of the Association of Edison Illuminating Companies,
in 1904: "The gearing originally employed consisted
of a friction-pulley upon the armature shaft, another friction-
pulley upon the driven axle, and a third friction-pulley which
could be brought in contact with the other two by a suitable
lever. Each wheel of the locomotive was made with
metallic rim and a centre portion made of wood or papier-
mache. A three-legged spider connected the metal rim of
each front wheel to a brass hub, upon which rested a collecting
brush. The other wheels were subsequently so equipped.
It was the intention, therefore, that the current should enter
the locomotive wheels at one side, and after passing through
the metal spiders, collecting brushes and motor, would pass
out through the corresponding brushes, spiders, and wheels
to the other rail."

As to the road: "The rails were light and were spiked to
ordinary sleepers, with a gauge of about three and one-half
feet. The sleepers were laid upon the natural grade, and
there was comparatively no effort made to ballast the road.
. . . No special precautions were taken to insulate the rails
from the earth or from each other."

The road started about fifty feet away from the generating
station, which in this case was the machine shop. Two
of the "Z" type dynamos were used for generating the current,
which was conveyed to the two rails of the road by
underground conductors.

On Thursday, May 13, 1880, at 4 o'clock in the afternoon,
this historic locomotive made its first trip, packed with as
many of the "boys" as could possibly find a place to hang
on. "Everything worked to a charm, until, in starting up
at one end of the road, the friction gearing was brought into
action too suddenly and it was wrecked. This accident
demonstrated that some other method of connecting the
armature with the driven axle should be arranged.

"As thus originally operated, the motor had its field circuit
in permanent connection as a shunt across the rails,
and this field circuit was protected by a safety-catch made
by turning up two bare ends of the wire in its circuit and
winding a piece of fine copper wire across from one bare
end to the other. The armature circuit had a switch in it
which permitted the locomotive to be reversed by reversing
the direction of current flow through the armature.

"After some consideration of the gearing question, it was
decided to employ belts instead of the friction-pulleys."
Accordingly, Edison installed on the locomotive a system of
belting, including an idler-pulley which was used by means
of a lever to tighten the main driving-belt, and thus power
was applied to the driven axle. This involved some slipping
and consequent burning of belts; also, if the belt were
prematurely tightened, the burning-out of the armature. This
latter event happened a number of times, "and proved to
be such a serious annoyance that resistance-boxes were
brought out from the laboratory and placed upon the locomotive
in series with the armature. This solved the difficulty.
The locomotive would be started with these resistance-boxes
in circuit, and after reaching full speed the operator could
plug the various boxes out of circuit, and in that way increase
the speed." To stop, the armature circuit was opened
by the main switch and the brake applied.

This arrangement was generally satisfactory, but the
resistance-boxes scattered about the platform and foot-rests
being in the way, Edison directed that some No. 8 B. & S.
copper wire be wound on the lower leg of the motor field-
magnet. "By doing this the resistance was put where it
would take up the least room, and where it would serve as
an additional field-coil when starting the motor, and it
replaced all the resistance-boxes which had heretofore been
in plain sight. The boxes under the seat were still retained
in service. The coil of coarse wire was in series with the
armature, just as the resistance-boxes had been, and could
be plugged in or out of circuit at the will of the locomotive
driver. The general arrangement thus secured was operated
as long as this road was in commission."

On this short stretch of road there were many sharp curves
and steep grades, and in consequence of the high speed attained
(as high as forty-two miles an hour) several derailments
took place, but fortunately without serious results.
Three cars were in service during the entire time of operating
this 1880 railroad: one a flat-car for freight; one an open
car with two benches placed back to back; and the third
a box-car, familiarly known as the "Pullman." This latter
car had an interesting adjunct in an electric braking system
(covered by Edison's Patent No. 248,430). "Each car axle had
a large iron disk mounted on and revolving with it between
the poles of a powerful horseshoe electromagnet. The pole-
pieces of the magnet were movable, and would be attracted
to the revolving disk when the magnet was energized, grasping
the same and acting to retard the revolution of the car axle."

Interesting articles on Edison's first electric railroad were
published in the technical and other papers, among which
may be mentioned the New York Herald, May 15 and July
23, 1880; the New York Graphic, July 27, 1880; and the
Scientific American, June 6, 1880.

Edison's second electric railroad of 1882 was more pretentious
as regards length, construction, and equipment. It
was about three miles long, of nearly standard gauge, and
substantially constructed. Curves were modified, and grades
eliminated where possible by the erection of numerous
trestles. This road also had some features of conventional
railroads, such as sidings, turn-tables, freight platform, and
car-house. "Current was supplied to the road by underground
feeder cables from the dynamo-room of the laboratory.
The rails were insulated from the ties by giving them
two coats of japan, baking them in the oven, and then placing
them on pads of tar-impregnated muslin laid on the ties.
The ends of the rails were not japanned, but were electroplated,
to give good contact surfaces for fish-plates and copper

The following notes of Mr. Frederick A. Scheffler, who designed
the passenger locomotive for the 1882 road, throw
an interesting light on its technical details:

"In May, 1881, I was engaged by Mr. M. F. Moore, who
was the first General Manager of the Edison Company for
Isolated Lighting, as a draftsman to undertake the work of
designing and building Edison's electric locomotive No. 2.

"Previous to that time I had been employed in the engineering
department of Grant Locomotive Works, Paterson,
New Jersey, and the Rhode Island Locomotive Works,
Providence, Rhode Island....

"It was Mr. Edison's idea, as I understood it at that time,
to build a locomotive along the general lines of steam locomotives
(at least, in outward appearance), and to combine
in that respect the framework, truck, and other parts
known to be satisfactory in steam locomotives at the same

"This naturally required the services of a draftsman accustomed
to steam-locomotive practice.... Mr. Moore was
a man of great railroad and locomotive experience, and his
knowledge in that direction was of great assistance in the
designing and building of this locomotive.

"At that time I had no knowledge of electricity.... One
could count so-called electrical engineers on his fingers then,
and have some fingers left over.

"Consequently, the ELECTRICAL equipment was designed by
Mr. Edison and his assistants. The data and parts, such as
motor, rheostat, switches, etc., were given to me, and my
work was to design the supporting frame, axles, countershafts,
driving mechanism, speed control, wheels and boxes,
cab, running board, pilot (or `cow-catcher'), buffers, and even
supports for the headlight. I believe I also designed a bell
and supports. From this it will be seen that the locomotive
had all the essential paraphernalia to make it LOOK like a
steam locomotive.

"The principal part of the outfit was the electric motor.
At that time motors were curiosities. There were no electric
motors even for stationary purposes, except freaks built for
experimental uses. This motor was made from the parts--
such as fields, armature, commutator, shaft and bearings,
etc., of an Edison "Z," or 60-light dynamo. It was the only
size of dynamo that the Edison Company had marketed at
that time.... As a motor, it was wound to run at maximum
speed to develop a torque equal to about fifteen horse-power
with 220 volts. At the generating station at Menlo Park
four Z dynamos of 110 volts were used, connected two in
series, in multiple arc, giving a line voltage of 220.

"The motor was located in the front part of the locomotive,
on its side, with the armature shaft across the frames, or
parallel with the driving axles.

"On account of the high speed of the armature shaft it
was not possible to connect with driving-axles direct, but
this was an advantage in one way, as by introducing an
intermediate counter-shaft (corresponding to the well-known
type of double-reduction motor used on trolley-cars since
1885), a fairly good arrangement was obtained to regulate
the speed of the locomotive, exclusive of resistance in the
electric circuit.

"Endless leather belting was used to transmit the power
from the motor to the counter-shaft, and from the latter to
the driving-wheels, which were the front pair. A vertical
idler-pulley was mounted in a frame over the belt from
motor to counter-shaft, terminating in a vertical screw and
hand-wheel for tightening the belt to increase speed, or the
reverse to lower speed. This hand-wheel was located in the
cab, where it was easily accessible....

"The rough outline sketched below shows the location
of motor in relation to counter-shaft, belting, driving-wheels,
idler, etc.:

"On account of both rails being used for circuits, . . . the
driving-wheels had to be split circumferentially and completely
insulated from the axles. This was accomplished by
means of heavy wood blocks well shellacked or otherwise
treated to make them water and weather proof, placed radially
on the inside of the wheels, and then substantially bolted
to the hubs and rims of the latter.

"The weight of the locomotive was distributed over the
driving-wheels in the usual locomotive practice by means
of springs and equalizers.

"The current was taken from the rims of the driving-wheels
by a three-pronged collector of brass, against which flexible
copper brushes were pressed--a simple manner of overcoming
any inequalities of the road-bed.

"The late Mr. Charles T. Hughes was in charge of the
track construction at Menlo Park.... His work was excellent
throughout, and the results were highly satisfactory so far
as they could possibly be with the arrangement originally
planned by Mr. Edison and his assistants.

"Mr. Charles L. Clarke, one of the earliest electrical
engineers employed by Mr. Edison, made a number of tests
on this 1882 railroad. I believe that the engine driving the
four Z generators at the power-house indicated as high as
seventy horse-power at the time the locomotive was actually
in service."

The electrical features of the 1882 locomotive were very
similar to those of the earlier one, already described. Shunt
and series field-windings were added to the motor, and the
series windings could be plugged in and out of circuit as
desired. The series winding was supplemented by resistance-
boxes, also capable of being plugged in or out of circuit.
These various electrical features are diagrammatically shown
in Fig. 2, which also illustrates the connection with the
generating plant.

We quote again from Mr. Hammer, who says: "The freight-
locomotive had single reduction gears, as is the modern practice,
but the power was applied through a friction-clutch
The passenger-locomotive was very speedy, and ninety
passengers have been carried at a time by it; the freight-
locomotive was not so fast, but could pull heavy trains at a
good speed. Many thousand people were carried on this
road during 1882." The general appearance of Edison's
electric locomotive of 1882 is shown in the illustration
opposite page 462 of the preceding narrative. In the picture
Mr. Edison may be seen in the cab, and Mr. Insull on the
front platform of the passenger-car.



WHILE the one-time art of telegraphing to and from moving
trains was essentially a wireless system, and allied in
some of its principles to the art of modern wireless telegraphy
through space, the two systems cannot, strictly speaking
be regarded as identical, as the practice of the former was
based entirely on the phenomenon of induction.

Briefly described in outline, the train telegraph system
consisted of an induction circuit obtained by laying strips
of metal along the top or roof of a railway-car, and the
installation of a special telegraph line running parallel with
the track and strung on poles of only medium height. The
train, and also each signalling station, was equipped with
regulation telegraph apparatus, such as battery, key, relay,
and sounder, together with induction-coil and condenser. In
addition, there was a special transmitting device in the shape
of a musical reed, or "buzzer." In practice, this buzzer was
continuously operated at a speed of about five hundred vibrations
per second by an auxiliary battery. Its vibrations were
broken by means of a telegraph key into long and short
periods, representing Morse characters, which were transmitted
inductively from the train circuit to the pole line
or vice versa, and received by the operator at the other end
through a high-resistance telephone receiver inserted in the
secondary circuit of the induction-coil.

The accompanying diagrammatic sketch of a simple form of
the system, as installed on a car, will probably serve to make
this more clear.

An insulated wire runs from the metallic layers on the
roof of the car to switch S, which is shown open in the sketch.
When a message is to be received on the car from a station
more or less remote, the switch is thrown to the left to con-
nect with a wire running to the telephone receiver, T. The
other wire from this receiver is run down to one of the axles
and there permanently connected, thus making a ground.
The operator puts the receiver to his ear and listens for the
message, which the telephone renders audible in the Morse

If a message is to be transmitted from the car to a receiving
station, near or distant, the switch, S, is thrown to the
other side, thus connecting with a wire leading to one end
of the secondary of induction-coil C. The other end of the
secondary is connected with the grounding wire. The primary
of the induction-coil is connected as shown, one end going
to key K and the other to the buzzer circuit. The other
side of the key is connected to the transmitting battery, while
the opposite pole of this battery is connected in the buzzer
circuit. The buzzer, R, is maintained in rapid vibration by
its independent auxiliary battery, B<1S>.

When the key is pressed down the circuit is closed, and
current from the transmitting battery, B, passes through
primary of the coil, C, and induces a current of greatly increased
potential in the secondary. The current as it passes
into the primary, being broken up into short impulses by
the tremendously rapid vibrations of the buzzer, induces
similarly rapid waves of high potential in the secondary, and
these in turn pass to the roof and thence through the intervening
air by induction to the telegraph wire. By a continued
lifting and depression of the key in the regular manner,
these waves are broken up into long and short periods,
and are thus transmitted to the station, via the wire, in
Morse characters, dots and dashes.

The receiving stations along the line of the railway were
similarly equipped as to apparatus, and, generally speaking
the operations of sending and receiving messages were
substantially the same as above described.

The equipment of an operator on a car was quite simple
consisting merely of a small lap-board, on which were
mounted the key, coil, and buzzer, leaving room for telegraph
blanks. To this board were also attached flexible conductors
having spring clips, by means of which connections
could be made quickly with conveniently placed terminals
of the ground, roof, and battery wires. The telephone receiver
was held on the head with a spring, the flexible connecting
wire being attached to the lap board, thus leaving the operator
with both hands free.

The system, as shown in the sketch and elucidated by
the text, represents the operation of train telegraphy in a
simple form, but combining the main essentials of the art
as it was successfully and commercially practiced for a number
of years after Edison and Gilliland entered the field.
They elaborated the system in various ways, making it more
complete; but it has not been deemed necessary to enlarge
further upon the technical minutiae of the art for the purpose
of this work.



ALTHOUGH many of the arts in which Edison has been a
pioneer have been enriched by his numerous inventions
and patents, which were subsequent to those of a fundamental
nature, the (so-called) motion-picture art is an exception,
as the following, together with three other additional patents[30]
comprise all that he has taken out on this subject:
United States Patent No. 589,168, issued August 31, 1897,
reissued in two parts--namely, No. 12,037, under date of
September 30,1902, and No. 12,192, under date of January
12, 1904. Application filed August 24, 1891.

[30] Not 491,993, issued February 21, 1893; No. 493,426,
issued March 14, 1893; No. 772,647, issued October 18, 1904.

There is nothing surprising in this, however, as the
possibility of photographing and reproducing actual scenes of
animate life are so thoroughly exemplified and rendered
practicable by the apparatus and methods disclosed in the
patents above cited, that these basic inventions in themselves
practically constitute the art--its development proceeding
mainly along the line of manufacturing details. That
such a view of his work is correct, the highest criterion--
commercial expediency--bears witness; for in spite of the
fact that the courts have somewhat narrowed the broad
claims of Edison's patents by reason of the investigations of
earlier experimenters, practically all the immense amount
of commercial work that is done in the motion-picture field
to-day is accomplished through the use of apparatus and
methods licensed under the Edison patents.

The philosophy of this invention having already been
described in Chapter XXI, it will be unnecessary to repeat
it here. Suffice it to say by way of reminder that it is
founded upon the physiological phenomenon known as the
persistence of vision, through which a series of sequential
photographic pictures of animate motion projected upon a
screen in rapid succession will reproduce to the eye all the
appearance of the original movements.

Edison's work in this direction comprised the invention
not only of a special form of camera for making original
photographic exposures from a single point of view with
very great rapidity, and of a machine adapted to effect the
reproduction of such pictures in somewhat similar manner
but also of the conception and invention of a continuous
uniform, and evenly spaced tape-like film, so absolutely
essential for both the above objects.

The mechanism of such a camera, as now used, consists of

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