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 115 



Benzol 136 



Amylene 

 Sulphuric ether 

 Formic ether 

 Acetic ether 



321 



440 

 548 

 612 



Bisulphide of carbon is the most transparent vapor in 

 this list; and acetic ether the most opaque; ifoth of an at- 

 mosphere of the former, however, produces 47 times the 

 effect of a whole atmosphere of air, while &th 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 80 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 



