i879-] 
Electric Lighting. 
*57 
This drove Mr. Starr to rely upon the second part of the 
specification, viz., that of using a small stick of carbon made 
incandescent in a Torricellian vacuum. He commenced 
with plumbago, and, after trying many other forms of carbon, 
found that which lines gas-retorts that have been long in use 
was the best. 
The carbon stick of square sedtion, about one-tenth of an 
inch thick and half an inch working length, was held ver- 
tically, 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 pro- 
jected beyond ; a similar wire passed downwards from the 
lower forceps, and dipped into the mercury of the tube, 
which was so long that when arranged as a barometer the 
enlarged end containing the carbon was vacuous. 
Considerable difficulty was at first encountered in sup- 
porting 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 bril- 
liant 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 bril- 
liant radiating surface. 
Some curious phenomena accompanied this illumination 
of the carbon. The mercury column fell to about half its 
barometric height, and presently the glass opposite the 
carbon stick became slightly dimmed by the deposition of a 
thin film cf sooty deposit. 
At first the depression of the mercury was attributed to 
the formation of mercurial vapour, and is described accord- 
ingly in the specification ; but further observation refuted 
this theory, for no return of the mercury took place when 
the tube was cooled. The depression was permanent. The 
formation of vaporous carbon was suggested by one of the 
capitalists ; but neither Mr. Starr nor myself was satisfied 
with this, nor with any other surmise we were able to make 
during Mr. Starr’s lifetime, nor up to the period of final 
abandonment of the enterprise. 
When this occurred the remaining apparatus was assigned 
to me, and I retained possession of the finally arranged tube 
and carbon for many years, and have shown it in adtion 
worked by a small Grove’s battery in the Town Hall of 
