488 



SCIENCE 



[N. S. Vol. XLI. No. 1057 



chemical means for "self-curing" any- 

 weak spots in the filament of his lamp. 

 The remedy was as ingenious as simple. In 

 preparing his filament, he passed the cur- 

 rent through it while the filament was 

 placed in an atmosphere of hydrocarbon 

 gas, so that in every spot where the tem- 

 perature rose highest on account of greater 

 resistance, brought about by the irregular 

 structure of the material, the hydrocarbon 

 gas was dissociated and carbon was depos- 

 ited automatically until the defect was 

 cured, with the result that the filament ac- 

 quired the same electric resistance over its 

 whole length. But this invention, however 

 brilliant, did not limit his efforts. He had 

 become imbued with the idea that the ideal 

 filament would be an absolutely structure- 

 less, homogeneous filament, with exactly 

 the same composition and the same section 

 throughout its whole length. He reasoned 

 that such a filament could not be obtained 

 from any natural products, neither from 

 paper nor bamboo, but that it had to be 

 produced artificially in the laboratory from 

 an absolutely uniform, structureless chem- 

 ical substance. After various unsuccessful 

 attempts, he finally secured this result by 

 applying his old knowledge of the days 

 when he used to make collodion. He pro- 

 duced a homogeneous, structureless trans- 

 parent film of nitrocellulose by evaporating 

 a solution of this material in suitable sol- 

 vents. As he could not carbonize this film 

 on account of the well-known explosive 

 properties of so-called "gun-cotton," he 

 obviated this difficulty by eliminating the 

 nitrate group of the molecule of cellulose- 

 nitrate by means of ammonium-sulphy- 

 drate. This gave him a flexible, transpar- 

 ent sheet, very similar in appearance to 

 gelatine; this material he called "Tami- 

 dine." Such films could be cut automat- 

 ically with utmost exactitude, producing 

 filaments of uniform section, which then 



could be submitted to carbonization, before 

 fastening them to the inside of the glass 

 bulb of the incandescent lamp. 



It is interesting to note here that the 

 modern Tungsten lamp, in all its perfec- 

 tion, made of ductile tungsten, is after all, 

 the fullest development of the principle 

 of an entirely structureless homogeneous 

 chemical filament. The Tungsten-filament 

 can stand much higher temperatures than 

 carbon and this property gives it higher 

 lighting efficiency, but the former tungsten 

 filaments of a few years ago, which had a 

 granular structure, had the same defect as 

 the earlier carbon lamps, namely, a non- 

 homogeneous texture and correspondent 

 short life. 



While Weston was wrestling with all his 

 electrical problems, and more particiilarly 

 with the construction of dynamos and 

 motors, he was handicapped continuously 

 by the clumsy and time-consuming meth- 

 ods of electrical measurements which were 

 the best existing at that period. Up till 

 then, these methods had been found good 

 enough for physical laboratories, where the 

 lack of accuracy did not result disas- 

 trously in hitting the pocket of the manu- 

 facturer, or where time — abundant time for 

 observations and calculations — was always 

 available. But progress in the electrical in- 

 dustries lagged behind the delay aud un- 

 certainties caused by electrical measure- 

 ments. So Weston was compelled to invent 

 for his own use a set of practical electrical 

 measuring instruments. It was not long 

 before some of his friends wanted very 

 badly duplicates of his instruments; be- 

 fore he knew it, he was giving considerable 

 attention to the construction and further 

 development of these instruments. Just 

 about this time, the electric light and dy- 

 namo construction enterprise entered into 

 a new period, where they began to develop 

 in large unwieldy commercial organiza- 



