ELECTRIC LIGHTING. 12 



ments with the large battery that I made consisting of 100 

 Daniell cells, with two square feet of working surface of each 

 element in each cell, and the copper-plates about three quarters 

 of an inch distant from the zinc satisfied all concerned that 

 neither platinum nor any available alloy of platinum and iridinm 

 could be relied upon, especially when the grand idea of sub- 

 dividing the light by interposing several platinum strips in the 

 same circuit, and working with a proportionally high power, 

 was carried out. 



This drove Mr. Starr to rely upon the second part of the 

 specification viz. that of using a small stick of carbon made in- 

 candescent in a Torricellian vacuum. He commenced with plum- 

 bago, and, after trying many other forms of carbon, found that 

 which lines gas-retorts that have been long in use to be the best. 



The carbon stick of square section, about one tenth of an 

 inch thick and half an inch working length, was held vertically, 

 by metallic forceps, at each end, in a barometer tube, the 

 upper part of which, containing the carbon, was enlarged to a 

 sort of oblong bulb. A thick platinum wire from the upper 

 forceps was sealed into the top of the tube and projected 

 beyond ; a similar wire passed downward from the lower for- 

 ceps, and dipped into the mercury of the tube, which was so 

 long that when arranged as a barometer the enlarged end con- 

 taining the carbon was vacuous. 



Considerable difficulty was at first encountered in supporting 

 this fragile stick. Metallic supports were not available, on 

 account of their expansion ; and, finally, little cylinders of 

 porcelain were used, one on each side of the carbon stick, and 

 about three eighths of an inch distant. 



By connecting the mercury cup with one terminal of the 

 battery, and the upper platinum wire with the other, a brilliant 

 and perfectly steady light was produced, not so intense as the 

 ordinary disruption arc between carbons, but equally if not 

 more effective, on account of the magnitude of brilliant radiat- 

 ing, surface. 



Some curious phenomena accompanied this illumination of 

 the carbon. The mercury column fell to about half its baro- 

 metric height, and presently the glass opposite the carbon 

 stick became slightly dimmed by the deposition of a thin film 

 of sooty deposit. 



At first the depression of the mercury was attributed to the 

 formation of mercurial vapor, and is described accordingly in 

 the specification ; but further observation refuted this theory, 



