The Electric Light.
An Authoritative Explanation of Edison’s Great Invention
Produced by Incandescence.
Why the Secret Has Been So Carefully Guarded.
A New Generator.
Menlo Park, N.J., Dec. 10, 1878 (source)
After a careful examination of Edison’s electric light, lasting several hours, during which all facilities were afforded me by the great inventor in person, I am enabled to give the readers of the HERALD the only authoritative description of the same thus far published. Hitherto there have appeared at intervals in journals, scientific and popular, both in Europe and America, so-called descriptions of the light, some absurd in their variance of truth, others approximating the real facts and one or two accurately hitting upon a part of Edison’s system; but none before the present have received his sanction. Yet the facts which I now present do not comprise the light in all its details, as many parts of the system, which is exceedingly complex, are not yet sufficiently protected by patents to warrant the inventor disclosing the same. The great anxiety of the thousands of other inventors all over the world who are eagerly working on the subject of electric lighting to learn his plans has made Edison unusually secretive, and, while willing to give the public at large the benefit of whatever he has accomplished, he feels it necessary to his own protection to withhold the secrets of his inventions and discoveries until such time as all are properly secured by patents. Scarcely a day passes without witnessing some anxious inquirers visiting Menlo Park in the hope of learning some of the inventor’s plans, and letters and telegrams inquiring, suggesting and proposing with reference to electric light arrive without number; but to all up to the present time that part of the laboratory containing the substance of the invention has been closed. Edison now, however, feels safe in acquainting the public with the contour of his system.
AN ERRONEOUS IMPRESSION.
First, it may be promised that the popular idea that Edison’s invention is embraced in one or two patents is exceeding erroneous. Before it is absolutely complete it will probably be covered in thirty or perhaps forty patents. Our patent laws do not permit the embracing in one set of specifications all the details of a complex plan — each distinct feature must be patented by itself. This was the case with Edison’s stock telegraph instrument, which, although not nearly so complex as the electric light, is protected by forty patents. It is also the case with his automatic system of telegraphy, the patents covering which number forty-six. His quadruplex telegraph, an apparatus a trifle in comparison with electric light so far as minute details are concerned, required for all its parts eleven patents. The various parts of the system of his electric lighting are probably as numerous and require as many patents for complete protection as did the system of lighten by gas, with its purifiers, gasometers, retorts and the hundred other appliances all going to make up the entire plan. Among the appliances of the electric light which will have to be secured before the light as an entirety can be explained are the improved dynamo machines, the regulators, condensers, switches and coolers, besides the different portions of the light proper and the various forms of conductors and lamps to meet the diversity in the wants of consumers. When all these are completed — and not a day passes without a marked advance toward their completion — the electric light of the wizard of Menlo Park will be ready for inspection, criticism and use, but not before.
IN THE LABORATORY.
I saw the Invention to-day under peculiarly favorable circumstances. The drenching rain and fierce tornado that beat against and almost rocked the laboratory had proved a boon to the inventor and his assistances affording them a day of comparative rest from the army of visitors that almost continually beset the wizard’s sanctum from Monday morning to Saturday night. Only one or two had braved the storm, and these were mild in their demands, insisting only on seeing the megaphone, tasimeter, and telephone, and graciously refraining from calling for songs and recitations from the phonograph and from asking for a detailed history of the progress of electric light from the beginning to the present time. On this account probably all the inmates were in good humor when I called. Mr. Griffin, the inventor’s private secretary, was poring over a batch of correspondence half a foot high, while he peacefully indulged in a meerschaum, filling the office with clouds of smoke. Mr. Batchelor, the chief assistant, was cheerily whistling over a lathe on which he was engaged. Edison himself was on the second floor of the laboratory, the picture of ease and content. Before him, on a table, were five or six lamps of his electric light, on which he had been recently working. The other members of the laboratory corps were engaged in various occupations. All seemed happy in the fact that they could pursue their several occupations without interruption.
“So two of your patents for the electric light have been allowed in Washington?” began your correspondent, explanatory of his visit.
“That’s what I hear,” replied the inventor, clearing away a pile of scientific books from a corner of the table to give more room to a few cells of a battery on the edge.
“Then you will soon be ready to make the secret public?”
“That don’t necessarily follow,” said Mr. Edison, still arranging the battery. “Two patents don’t amount to much when thirty or forty are necessary. I am not yet advised which claims have been allowed. My solicitor informs me that the claims allowed are numbers 156 and 162, but what particular points they cover I can’t now say.”
“Then you have other patents pending?”
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“By all means. I have at the present time eleven in the Patent Office. The system, you know, is a little complex.”
After some further preliminary conversation Edison accorded me the privilege of examining in detail the lamp and the other appliances going to make up the light, explaining the parts with a logical conciseness that brought out all in perfect clearness. I took down the points in detail and submitted the same to his inspection to insure accuracy. After revising and correcting the same, and in some places striking out parts as describing the invention too much detail, he gave his approval.
HOW THE LIGHT IS PRODUCED.
The light is produced by incandescence. The conductor, which is made incandescent by the electrical current passing through it, is a small, curiously shaped apparatus, consisting of a high alloy of platinum and iridium, which cannot be melted under 5,000 degrees Fahrenheit. A sufficient quantity of this metal is placed in each burner to give a light equal to that of a gas jet. Devices of exceeding simplicity, and, as repeated experiments have proved, of equal reliability, are connected with the lamp. The surmount the apparent impossibility of regulating the strength of the light. This lamp, when placed in the electric circuit in which a strong current circulates is absolutely independent of the strength of the current. This Edison considers one of the vital features of the invention. Thus, if the regulator is set so that the light gives only, say, ten candle power, no increase in the strength of the current will increase its brilliancy.
EACH LIGHT INDEPENDENT.
Each light is independent of all others in the circuit. A thousand may be fed from the same conductor and the extinguishing of all but one will have on that one, Edison claims, no perceptible effect. Each lamp in the circuit, by means of the regulator, a description of which latter Edison for the present withholds, is allowed to draw from the central station just sufficient current to supply itself. In lighting by incandescence the light is obtained by the resistance which the conductor in the lamp offers to the passage of electric current. Hence any other resistance exterior to the lamp used therewith to regulate it requires a current in proportion to its resistance although it gives no light. One of the main features of Edison’s invention consists in having all the resistance outside of the main conductor produce light, consequently there is maximum economy. The lamp devised by Edison is not merely a coil of incandescent metal, but a very peculiar arrangement of such metal whereby (by means of a discovery of his in connection with radiant energy) a much weaker current is made to generate a give light than if a simple spiral were used, and the considerable loss due to the division of light is compensated for.
INCANDESCENCE VS. CARBON.
It has been acknowledged by nearly all electricians that lighting by incandescence, especially incandescence of a metallic wire, offers less obstacle to the division of electric light than by any other method, and Edison believes it to be the only reliable method, because the light giving metal is an electrical “constant” whose resistance can always be known and depended upon — a condition which is exceedingly essential when many hundreds of lights must be supplied from one conductor. In the case of the electric arc between carbon rods, now so freely used, the resistance varies at every instant, not only from changes in the strength of the current, but from impurities in the carbon, from air currents and from many other causes. On this account Mr. Edison claims that factors so variable coming in play in hundreds of lamps make it impossible to calculate the strength of the current or size of the conductors. It would be as difficult as supplying gas from one main where each burner varied from excessive limits with the rapidity of lightning. Besides in the case of carbon points many hundreds reacting on each other cause such an unsteadiness in the light as to be unbearable. Lighting by incandescence Edison claims is free from any of these defects.
Since Edison undertook the problem of lighting by incandescence many attempts have been made in the same direction, but owing either to a lack of knowledge or a misconception of the cost of electricity, the devices and improvements were such that as much current had to be supplied when the lamps were not lighted as when they were. Great loss was in consequence entailed.
Edison’s electric light may be briefly summed up in saying that the lamps used give a light by incandescence of five, ten, or fifteen candle power. It gives off no deleterious gases. No consumption of material takes place and the proportion of heat to light is infinitely less than that from a gas jet.
THE SECRET ARCHIVES.
Whether he will permit to be made public the specifications of the claims for which patents have just been allowed Edison has not yet decided. Should he deem it necessary for his protection for the subsequent patents he may under the Patent laws, file the specifications in the secret archives of the Patent Office for a period sufficiently long to enable him to secure the necessary patents. Yesterday another specification for a British Patent was sent by him to his patent solicitor, making the third protecting his light in Great Britain.
LIGHT FROM ONE CELL OF BATTERY.
In the course of his experiments on the electric light Edison made the discovery that he could, by a certain combination in the form of the metal used in his lamp, secure sufficient light from the electricity generated from one cell of battery to enable him to read by. The cell used was an ordinary one of Daniels’ battery. To his surprise — for he hardly expected such a result — the thin metal soon became a dull red. By changing the form again he produced a brighter red, and, after several other changes, he succeeded in obtaining a glow which made it not at all difficult to read by the room being dark. Several of the laboratory hands examined the phenomenon with curiosity. It served to demonstrate to Mr. Edison that he had hit upon the form of metal to produce the best result.
Another new feature in the system of the light as a whole is his improvement on dynamo machine specifications, for a patent for which Mr. Edison has only just applied.
