RADIATION. 57 



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 

 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 bibu- 

 lous 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 pat- 

 chouli acts more feebly on radiant heat than any other 

 perfume yet examined. Here follow the results ob- 

 tained with various essential oils, the odour, in each 

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

 tube already employed for gases and vapours : 



Name of perfume Absorption 



Patchouli 30 



Sandal wood . 

 Geranium 

 Oil of cloves , 

 Otto of roses , 



32 

 33 

 34 

 37 



Bergamot 44 



Neroli 47 



Lavender 60 



Lemon 65 



Portugal 67 



Thyme 68 



Kosemary ..... 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 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. 



