RADIATION. 



57 



wave-motion intercepted by the ether would be many 

 thousand times that intercepted by the air. 



Any one of these vapours discharged into the free 

 atmosphere, in front of a body emitting obscure rays, 

 intercepts more or less of the radiation. A similar ef- 

 fect is produced by perfumes diffused in the air, though 

 their attenuation is known to be almost infinite. Car- 

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

 paper, moistened by patchouli, the scent takn up by 

 the current absorbs 30 times the quantity of heat inter- 

 cepted by the air which carries it; and yet patchouli 

 acts more feebly on radiant heat than any other per- 

 fume yet examined. Here follow the results obtained 

 with various essential oils, the odour, in each case, being 

 carried by a current of dry air into the tube already em- 

 ployed for gases and vapours: 



Name of perfume 

 Patchouli 

 Sandal wood . 

 Geranium 

 Oil of cloves 

 Otto of roses . 



Absorption 



Bergamot 44 



Neroli 47 



Lavender . . 60 



Lemon ... .65 



Portugal . 67 



Thyme ... 68 



Rosemary . . 74 



Oil of laurel . 80 



Camomile flowers . 87 



Cassia ... 109 



Spikenard .... . ..856 



Aniseed ........ 872 



Thus the absorption by a tube full of dry air being 

 1, that of the odour of patchouli diffused in it is 30, 

 that of lavender 60, that of rosemary 74, whilst that of 

 aniseed amounts to 372. It would be idle to speculate 

 on the quantities of matter concerned in these actions. 



