Bisulphide of carbon is the most transparent vapour in this list; and acetic ether the most opaque; 1/60th of an atmosphere of the former, however, produces 47 times the effect of a whole atmosphere of air, while 1/60th 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 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 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 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 32 Geranium 33 Oil of cloves 34 Otto 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 odour of patchouli diffused in it is 30, at of lavender 60, that of rosemary 74, whilst that of aniseed amounts to 372. It would be idle to speculate the quantities of matter concerned in these actions. ******************** 12. Aqueous Vapour in relation to the Terrestrial Temperatures.