‘ 
162 On the Production of Light by Chemical Action. 
When the coal was first taken from the fire, and was burning 
very intensely, on looking through the telescope I saw all the 
colored rays of the spectrum in their proper order. I had pre- 
viously passed through the slit a beam of the sun light, reflected 
from a mirror, that I might have a standard spectrum with fixed 
lines. Now when the coal was burning at its utmost vigor, the 
spectrum it gave did not seem to me to differ either as respects 
length or the distribution of its colors from the spectrum of sun- 
light. But as the combustion declined, and the coal burnt less 
brightly, I saw that its spectrum was becoming less and less, 
the shortening taking place at the more refrangible extremity, 
“one ray after another disappearing in due succession. First the 
violet became extinct, then the indigo, then the blue, then the 
green ; until at last the red with an ash gray light occupying the 
place of the yellow, was aloné visible, and presently this also 
went out. 
From numerous experiments of this sort, I conclude that there 
is a connexion between the refrangibility of the light which a burn- 
ing body yields, andethe intensity of the chemical action going 
on; and that the refrangibility always increases as the chemical 
action increases. It may perhaps be objected by some that in 
the form of experiment here introduced two totally different 
things are confounded ; and that the burning coal not only gives 
forth its rays as a combustible body, strictly speaking, but also 
as an incandescent mass. 
To avoid this objection as far as possible, and also to reach a 
much higher temperature than could have been otherwise obtain- 
ed, I threw a stream of oxygen gas on that portion of the an- 
thracite which was opposite the slit; but my expectations were 
disappointed, for instead of the combustion being increased, the 
coal was actually extinguished by the jet playing on it. I there- 
fore replaced the anthracite with a flat piece of well burnt char- 
fade away in succession. By merely turning the stopcock, through 
which the oxygen came, I could reéstablish the original colors 
or witness their decline. And it was very interesting to see with 
what unerring regularity as the chemical action became more in- 
tense the more refrangible colors were developed; and how as 
it declined they disappeared in due succession. ‘The final tint 
