on the Light emitted from various Bodies . 421 
light gradually returned. The experiment was thrice repeated, 
and with the same result. 
OBSERVATION. 
This species of gas, we observe to have totally prevented the 
emission of light, and to have quickly extinguished that which 
had been emitted : likewise that the luminous objects which had 
been under its influence, (except the glow-worm) did not expe- 
rience a revival of their light, when taken out, and kept for some 
time in common air. 
§ VIII. 
The Effects of a Vacuum on spontaneous Light . 
EXPERIMENTS. 
Exper. 1 . A piece of shining wood, of a moderate size, was 
put under the receiver of an air-pump, in a dark room ; in 
proportion as the air was extracted, the light was gradually ex- 
tinguished, and at last reduced to a mere point, just visible, 
owing most probably to a small residuum of air, which is always 
left, even in the most perfect machine. Fresh air was then 
leisurely admitted, and the light was immediately revived in 
a very beautiful manner. This experiment was frequently 
repeated, and always with the like effect. 
Exper. 2. Some luminous matter of a herring, uncommonly 
bright, was smeared upon a piece of red blotting paper, and 
then submitted to the operation of the air-pump. The light be- 
came fainter and fainter, as the inclosed air was withdrawn, and 
at last nearly vanished; but brightened up as before, on the 
