50 
have been anticipated that at high temperatures the most 
dense and refractory substances would vaporise while re- 
taining their solid form. 
The conditions necessary for observing the behaviour of 
solids at high temperatures are well brought about in the 
modern form of incandescent electric lamp. This lamp con- 
sists of a bulb of glass from which the air is exhausted to 
the highest degree attainable, and a filament of metal or 
carbon is mounted in the bulb, and rendered incandescent 
by the action of the electric current. 
Platinum, from its high degree of infusibility, was con- 
sidered by some the most suitable substance for the luminous 
filament, and great expectations were formed, that by its 
use the problem of incandescent lighting would be solved. 
It was, however, found that an atmosphere of platinum 
vapour was formed in the interior of the bulb, which, after 
the lamp had been in action a lengthened number of hours, 
condensed on the surface of the glass and formed a bright 
reflecting surface like a mirror. 
This property of the platinum, while affording a remark- 
able illustration of the vaporisation of a dense body while 
retaining its solid form, was fatal to its use as an illuminant, 
as the density of the film of platinum on the surface of the 
glass ultimately obstructed the greater portion of the light 
from the filament itself. 
Chemists, I believe, are not unanimous in opinion as to 
whether elementary carbon ever passes from the solid to 
the liquid form. 
Some years ago, I frequently made the experiment of 
concentrating upon a small pencil of carbon, two inches long 
and three twentieths of an inch in diameter, an amount of 
electric force sufficient to fuse a rod of platinum two feet 
long and a quarter of an inch in diameter. 
The light from the pencil was of intense whiteness, but 
the carbon showed no signs of fusion, and rapidly diminished 
in thickness by combination with the oxygen of the air. 
