414 FRAGMENTS OF SCIENCE 



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 oscillat- 

 ing 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 68 per cent of the radiation from the 

 hydrogen flame; but when the flame and spiral are em- 

 ployed, 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 platinum 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 flame. 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 carbon, as first proved by Melloni, 

 is in some measure transparent to the ultra-red rays, and 

 I have myself succeeded in transmitting between 40 and 



* This was soon afterward accomplished. See pp. 63-66. 



