. Electrical world. they would last but an hour or two. We tried a great manyexperiments with paper carbons, wood carbons and some made fromcarbonized broom corn. What we desired at that date, and hadsettled our minds upon as the only possible solution of the subdivi-sion of the electric light, was that the lamps must have a high re-sistance and small radiating surface. About December, 1878, I engaged as my mathematician Mr. Francis R. Upton, who hadlately studied under Helmholtz, in Germany, and he helped megreatly in calculations of the multiple arc problem. Our figuresproved that the lamp m
. Electrical world. they would last but an hour or two. We tried a great manyexperiments with paper carbons, wood carbons and some made fromcarbonized broom corn. What we desired at that date, and hadsettled our minds upon as the only possible solution of the subdivi-sion of the electric light, was that the lamps must have a high re-sistance and small radiating surface. About December, 1878, I engaged as my mathematician Mr. Francis R. Upton, who hadlately studied under Helmholtz, in Germany, and he helped megreatly in calculations of the multiple arc problem. Our figuresproved that the lamp must have at lea^t 100 ohms resistance tocompete successfully with gas; for if the lamps were of low re-sistance the cost of the copper main conductors would be so greatas to render the system uneconomical and commercially imprac-ticable. In this direction we tried platinum also; and when workingon incandescent platinum we had procured a Sprengel mercurypump and had ascertained that we could thus get exceedingly high. FIG. I.—FIRST PHOTOGRAPH TAKEN BY INCANDESCENT LIGHT. (Reproduction of Photograph taken by Mr. Edison at his Menlo[ark Laboratory at midnight about Dec. 20, 1879, by the light of threeof his first electric lamps. The portrait is that of .Mr. CharlesBatchelor.) vacua. It occurred to me that perhaps a filament of carbon couldbe made to stand in the sealed glass vessels or bulbs, which we wereusing, exhausted to a high vacuum. Separate lamps were madein this way independent of the air pump, and in October, 1879, ^^^made lamps of paper carbon, and with carbons of common sewingthread, placed in a receiver or bulb made entirely of glass, with theleading-in wires sealed in by fusion. The whole thing was exhaustedby the Sprengel pump to nearly one-millionth of an filaments of carbon, although naturally quite fragile owing totheir length and small mass, had a smaller radiating surface and
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
