The Invention Of The Incandescent Lamp - 9

The Invention Of The Incandescent Lamp - 9

In obtaining this perfection of vacuum apparatus, Edison realized that he was

approaching much nearer to a solution of the problem. In his experiments with the

platinum-iridium lamps, he had been working all the time toward the proposition of high

resistance and small radiating surface, until he had made a lamp having thirty feet of fine

platinum wire wound upon a small bobbin of infusible material; but the desired economy,

simplicity, and durability were not obtained in this manner, although at all times the

burner was maintained at a critically high temperature. After attaining a high degree of

perfection with these lamps, he recognized their impracticable character, and his mind

reverted to the opinion he had formed in his early experiments two years before --viz.,

that carbon had the requisite resistance to permit a very simple conductor to accomplish

the object if it could be used in the form of a hair-like "filament," provided the filament

itself could be made sufficiently homogeneous. As we have already seen, he could not

use carbon successfully in his earlier experiments, for the strips of carbon he then

employed, although they were much larger than "filaments," would not stand, but were

consumed in a few minutes under the imperfect conditions then at his command.

Now, however, that he had found means for obtaining and maintaining high vacua,

Edison immediately went back to carbon, which from the first he had conceived of as the

ideal substance for a burner. His next step proved conclusively the correctness of his old

deductions. On October 21, 1879, after many patient trials, he carbonized a piece of

cotton sewing- thread bent into a loop or horseshoe form, and had it sealed into a glass

globe from which he exhausted the air until a vacuum up to one-millionth of an

atmosphere was produced. This lamp, when put on the circuit, lighted up brightly to

incandescence and maintained its integrity for over forty hours, and lo! the practical

incandescent lamp was born. The impossible, so called, had been attained; subdivision of

the electric- light current was made practicable; the goal had been reached; and one of the

greatest inventions of the century was completed. Up to this time Edison had spent over

$40,000 in his electric-light experiments, but the results far more than justified the

expenditure, for with this lamp he made the discovery that the FILAMENT of carbon,

under the conditions of high vacuum, was commercially stable and would stand high

temperatures without the disintegration and oxidation that took place in all previous

attempts that he knew of for making an incandescent burner out of carbon. Besides, this

lamp possessed the characteristics of high resistance and small radiating surface,

permitting economy in the outlay for conductors, and requiring only a small current for

each unit of light--conditions that were absolutely necessary of fulfilment in order to

accomplish commercially the subdivision of the electric-light current.

This slender, fragile, tenuous thread of brittle carbon, glowing steadily and continuously

with a soft light agreeable to the eyes, was the tiny key that opened the door to a world

revolutionized in its interior illumination. It was a triumphant vindication of Edison's

reasoning powers, his clear perceptions, his insight into possibilities, and his inventive

faculty, all of which had already been productive of so many startling, practical, and

epoch-making inventions. And now he had stepped over the threshold of a new art which

has since become so world-wide in its application as to be an integral part of modern

human experience.[9]

[9] The following extract from Walker on Patents (4th edition) will probably be of

interest to the reader:

"Sec. 31a. A meritorious exception, to the rule of the last section, is involved in the

adjudicated validity of the Edison incandescent-light patent. The carbon filament, which

constitutes the only new part of the combination of the second claim of that patent, differs

from the earlier carbon burners of Sawyer and Man, only in having a diameter of onesixty-

fourth of an inch or less, whereas the burners of Sawyer and Man had a diameter of

one-thirty-second of an inch or more. But that reduction of one-half in diameter increased

the resistance of the burner FOURFOLD, and reduced its radiating surface TWOFOLD,

and thus increased eightfold, its ratio of resistance to radiating surface. That eightfold

increase of proportion enabled the resistance of the conductor of electricity from the

generator to the burner to be increased eightfold, without any increase of percentage of

loss of energy in that conductor, or decrease of percentage of development of heat in the

burner; and thus enabled the area of the cross-section of that conductor to be reduced

eightfold, and thus to be made with one-eighth of the amount of copper or other metal,

which would be required if the reduction of diameter of the burner from one-thirtysecond

to one-sixty- fourth of an inch had not been made. And that great reduction in the

size and cost of conductors, involved also a great difference in the composition of the

electric energy employed in the system; that difference consisting in generating the

necessary amount of electrical energy with comparatively high electromotive force, and

comparatively low current, instead of contrariwise. For this reason, the use of carbon

filaments, one-sixty-fourth of an inch in diameter or less, instead of carbon burners onethirty-

second of an inch in diameter or more, not only worked an enormous economy in

conductors, but also necessitated a great change in generators, and did both according to a

philosophy, which Edison was the first to know, and which is stated in this paragraph in

its simplest form and aspect, and which lies at the foundation of the incandescent electric

lighting of the world."

No sooner had the truth of this new principle been established than the work to establish

it firmly and commercially was carried on more assiduously than ever. The next

immediate step was a further investigation of the possibilities of improving the quality of

the carbon filament. Edison had previously made a vast number of experiments with

carbonized paper for various electrical purposes, with such good results that he once

more turned to it and now made fine filament-like loops of this material which were put

into other lamps. These proved even more successful (commercially considered) than the

carbonized thread--so much so that after a number of such lamps had been made and put

through severe tests, the manufacture of lamps from these paper carbons was begun and

carried on continuously. This necessitated first the devising and making of a large

number of special tools for cutting the carbon filaments and for making and putting

together the various parts of the lamps. Meantime, great excitement had been caused in

this country and in Europe by the announcement of Edison's success. In the Old World,

scientists generally still declared the impossibility of subdividing the electric-light

current, and in the public press Mr. Edison was denounced as a dreamer. Other names of

a less complimentary nature were applied to him, even though his lamp were actually in

use, and the principle of commercial incandescent lighting had been established.