Page:Science vol. 5.djvu/369

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��Inportance, for the quantity of light emitted by a glowing mibatance rises Iti a niore rapid proportion tb«n the teinperatUK of lliat substiince.

In 1S33 we find Professor Jobard of Bnissela say- ing Dial " a ainail atrip of carlHiii In a racunni, used ki a conductor of ft current of electricity, wouJd emit «n Intense, fixed, and durable light." DeChangy, a former pupil of Jnbard, seems to have tjilien these word:) as adrice, for be commenced hi* experiments Ln that line almost Immeillately afterwanls. About this time au Englishman named Moie^nB also made an incandescent lump by using platinum. De- Changy'a Bxperinienla failed because ihe strips of gas-carbon whlcii lie usmI became dUlulegrated by the current, and, as his globes were not perfectly ex- hausted or sealed, the carbon gradually consumed

At>out the year 1S48, J. W. Starr of Cincinnati entered upon a thordy a mnnillcent promoter of his plana. After helping Starr in every way, Teabody sent liim to England W exhibit his invention. Before start- Ing on hla voy>igt>, Starr procured himself a compan- ion named King, a shrewd man of busine.'^s. who Immediately had a ta:^ chandelier constructed with twenty-six electric glow-lnnips, which were to sym- bolize the stall's of the Union. The novel spectacle WIS gated upon by large crowds; and Parad&y, after witnessing the extierlments, f-igniSed to his American brother electrician his great satisfaction with the result.

Siarr died on Ihe return voya^ie, and King patented the lamp In his own name. This patent was granted on the 4lh of November, 19JS. and refers to ' a glow- ing carbon strip in a vacuum.' But with the death of Starr the necessary funds ceased to How, and in a short time the promising glow-lamp was consigned to oblivion.

A very similar fate befell the inventions of the Englishmen Greener and Staite, who patented, in 1848, another carbon-lamp. Siarr formed the neces- sary vacuum by using a tube th I rty-slz Inches long, filled with mercury; but the generation of electricity wa4 at that time far too expensive, although as re- gards the clearness of the light, and the durability of the carbon, the lamp was a success.

In 1S48 Petrie proposed to patent Ihe use of Iridi- um, but the scarcity of that metal rendere<i It out of the question. In 1835 DeChangy resumed his stud- ies with renewed xeai, occupying himself with the construction of a lamp in which platinum formed the conductor, and In IS-'iS patented a current r^- ulator which enabled bim to use his lamps for the illumination of mines, submerged for flshing-pur- poaes, and in a nautical telegraph aystem by which signals were displayed from the niast-lieads of vessels. The plulinum was submitted to a preparing process of separation, being maintained heated fur some time at a moderate degree oF redness, and then gradually raised to Lhat d^ree of heat to which it would be afterwards subjected in the lamp.

At intervals of ten and Rfteen years after the in- ventions of Starr and of DeChangy, Ihe incandescent

��Itttnp WM rsTived, with partial success; but It was not until Edison and Swan put their shoulders to the wheel that a perfect an<l practical lamp was con- structed.

In the year 1878 Edison was journeying In the Rocky Uountains, when a companion awakened within him the desire of occupying himself with electric lighting, and on his return to Menln Park he furnished himself with the necessary apparatus. Like DeChangy, he imagined ilmt it would be easier to use metal than carbon; and. wltli the abundant funds furnished bim by the Edison electric-lighting company, be was enabled to reach aiinoat every sub- stance which his fertile bruin might surest. For instance: It Is said that his attention was called to thorium, — a metal particularly difficult lo fuse; and, when a mineralogist informed him that lliere was not a half-ounce of thorium in the whole lerrilory of the United Slates, Edlann called up one of his assist- ants, and, telling him that in one of the goUi-mlnes of the north-west a qnaniliy of monarlie crystals (from which thorium Isextrncledl had been found, gave hUn a letter of credit, with Instnictlons lo bring him ill the shortest possible time a hundred pounds of monarite. In a few weeks Edi<nn had the uiona- rite, and forthwith began his cxperiraeula. But thorium also failed; and pialimim was again tried, this time with a certain amount of snccesi'.

Meanwhile the dynamo-machine and Ihe Sprengei air-pumphad been perfected. An Englishman named J, W. Swan now obtained fair results with a fliament of charred cardboard, and found that the rapid con- sumption and consequent breaking of the glowing carbon was an almost Insuperable Impediment to his success, and he also found that the Inner walls of his lamp became darkened by a deposit of some kind. These troubles must have been of a most alarming character. But Swan went on, and obtained the co- operation of a Mr. Steam, who was considered a great authority as regards perfect vacuum. Evidently he also fully understood that thi^ carbon must be pre- viously lieated to whlteoess in a good vacuum; and Id 1877 he sent to Mr. Steam a quantity of carbon- ized cardboard strips.requestiiig that they be mounted In glass bulbs, subsequently to be exhausted as per- fectly as possible. This st'ems to have been done with rare ability by raising Ihe carbon to a very high degree of heat by means of an electric current, which set free thegasi's It contained, and after tranls removed them. The ends of the dlaments were also made thicker; and when the connections were made good, and the vacuum sufficient, the glass bulb containing the glowing carbon did not blacken, and the con- sumption of the filament was Infinilesimally small. There only remained to make the lamp mechanically perfect; and In 1978 Swan publicly exhibited his glow- lamp, which possessed all the essential characteristica of that in use at present. In the same year Bdlaon discarded metals, and followed In the footsteps of Ihe carbon men. Being forestalled by Swan, Mr. Edison could not use cotton thread In his lamp, and, after a lu:'7 series of experiments, decided u|H)n the use of fiiaraenta made out of a species of bamboo.

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