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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 practice.
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.
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