440 FRAGMENTS OF SCIENCE. 



mits 57 per cent, of the same radiation ; alcohol absorbs 

 67 and transmits 33 per cent., and alcohol, as an absorber 

 of radiant heat, stands at the head of all liquids except 

 one. The exception is water. A layer of this sub- 

 stance, of the thickness above given, absorbs 81 per 

 cent., and permits only 19 per cent, of the radiation to 

 pass through it. Had no single experiment ever been 

 made upon the vapour of water, its vigorous action upon 

 radiant heat might be inferred from the deportment of 

 the liquid. 



The relation of absorption and radiation to the 

 chemical constitution of the radiating and absorbing 

 substances was next briefly considered. For the first 

 six substances in the list of liquids examined, the radiant 

 and absorbent powers augment as the number of atoms 

 in the compound molecule augments. Thus, bisulphide 

 of carbon has 3 atoms, chloroform 5, iodide of ethyl 8, 

 benzol 12, and amylene 15 atoms in their respective 

 molecules. The order of their power as radiants and 

 absorbents is that here indicated, bisulphide of carbon 

 being the feeblest, and amylene the strongest of the six. 

 Alcohol, however, excels benzol as an absorber, though 

 it has but 9 atoms in its molecule ; but, on the other 

 hand, its molecule is rendered more complex by the 

 introduction of a new element. Benzol contains car- 

 bon and hydrogen, while alcohol contains carbon, 

 hydrogen and oxygen. Thus, not only does atomic 

 multitude come into play in absorption and radiation 

 atomic complexity must also be taken into account. 

 I would recommend to the particular attention of 

 chemists the molecule of water ; the deportment of this 

 substance towards radiant heat being perfectly anoma- 

 lous, if the chemical formula at present ascribed to it 

 be correct. 



Sir William Herschel made the important discovery 



