42 FRAGMENTS OF SCIENCE. 



Bisulphide of carbon is the most transparent vapor in 

 this list; and acetic ether the most opaque; one-sixtieth of an 

 atmosphere of the former, however, produces 47 times the 

 effect of a whole atmosphere of air, while one-sixtieth of an 

 atmosphere 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 together, 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 atmos- 

 phere, 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 current 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 examined. Here follow 

 the results obtained with various essential oils, the odor, 

 in each case, being carried by a current of dry air into the 

 tube already employed for gases and vapors: 



Name of perfume. Absorption. 



Patchouli 30 



Sandal wood 32 



Geranium 33 



Oil of cloves : 34 



Attar of roses 37 



Bergamot 44 



Neroli 47 



Lavender 60 



Lemon 65 



Portugal 67 



Thyme 68 



Rosemary 74 



Oil of laurel 80 



Camomile flowers 87 



Cassia 109 



Spikenard 355 



Aniseed 372 



Thus the absorption by a tube full of dry air being 1, 

 that of the odor of patchouli diffused in it is 30, that of 

 lavender 60, that of rosemary 74, while that of aniseed 



