CONTRIBUTIONS TO MOLECULAR PHYSICS. 299 
secondly, in the circumstance that the lime is heated by 
the collision of the molecules of aqueous vapor, before 
their heat has assumed the radiant form. But it cannot 
be doubted that the same effect would be produced by 
radiant heat of the same periods, provided the motion of 
the ether could be rendered sufficiently intense.* The 
effect in principle is the same, whether we consider the 
lime to be struck by a particle of aqueous vapor oscillating 
at a certain rate, or by a particle of ether oscillating at the 
same rate. 
By plunging a platinum wire into a hydrogen flame we 
cause it to glow, and thus introduce shorter periods into 
the radiation. These, as already stated, are in discord 
with the atomic vibrations of water: hence we may infer 
that the transmission through water will be rendered more 
copious by the introduction of the wire into the flame. 
Experiment proves this conclusion to be true. Water, 
from being opaque, opens a passage to 6 per cent, of the 
radiation from the spiral. A thin plate of colorless glass, 
moreover, transmits 58 per cent, of the radiation from the 
hydrogen flame; but when the flame and spiral are 
employed, 78 per cent, of the heat is transmitted. 
For an alcohol flame Knoblauch and Melloni found glass 
to be less transparent than for the same flame with a plati- 
num spiral immersed in it; but Melloni afterward showed 
that the result was not general that black glass and black 
mica were decidedly more diathermic to the radiation from 
the pure alcohol flrime. Melloni did not explain this, but 
the reason is now obvious. The mica and glass owe their 
blackness to the carbon diffused through them. This car- 
bon, as first proved by Melloni, is in some measure trans- 
parent to the ultra-red rays, and I have myself succeeded 
in transmitting between 40 and 50 per cent, of the radia- 
tion from a hydrogen flame through a layer of carbon whioh 
intercepted the light of an intensely brilliant flame. The 
products of combustion of alcohol are carbonic acid and 
aqueous vapor, the heat of which is almost wholly ultra-red. 
For this radiation, then, the carbon is in a considerable 
degree transparent, while for the radiation from the plati- 
num spiral, it is in a great measure opaque. The platinum 
wire, therefore, which augmented the radiation through 
the pure glass, augmented the absorption of the black glass 
and mica. 
* This was soon afterward accomplished. See pp. 35, 36. 
