62 FRAGMENTS OF SCIENCE 



are the absorptions effected by a series of vapors at a 

 pressure of &th of an atmosphere: 



Name of vapor Absorption 



Bisulphide of carbon ....... 47 



Iodide of methyl . f '- J ... ..... 115 



Benzol 136 



Amylene . . . 321 



Sulphuric ether 440 



Formic ether 548 



Acetic ether . .612 



Bisulphide of carbon is the most transparent vapor in 

 this list; and acetic ether the most opaque; i&th of an at- 

 mosphere of the former, however, produces 47 times the 

 effect of a whole atmosphere of air, while ?foth of an atmos- 

 phere of the latter produces 612 times the effect of a whole 

 atmosphere of air. Reducing dry air to the pressure of the 

 acetic ether here employed, and comparing them then to- 

 gether, the quantity of wave-motion intercepted by the 

 ether would be many thousand times that intercepted by 

 the air. 



Any one of these vapors discharged into the free 

 atmosphere, in front of a body emitting obscure rays, 

 intercepts more or less of the radiation. A similar effect 

 is produced by perfumes diffused in the air, though their 

 attenuation is known to be almost infinite. Carrying, 

 for example, a current of dry air over bibulous paper, 

 moistened by patchouli, the scent taken up by the cur- 

 rent absorbs 30 times the quantity of heat intercepted 

 by the air which carries it; and yet patchouli acts more 

 feebly on radiant heat than any other perfume yet ex- 

 amined. Here follow the results obtained with various 

 essential oils, the odor, in each case, being carried by 



