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 be
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.

We are now fully prepared for a result which, without such
preparation, might appear incredible. Water is, to some extent, a
volatile body, and our atmosphere, resting as it does upon the surface
of the ocean, receives from it a continual supply of aqueous vapour.
It would be an error to confound clouds or fog or any visible mist
with the vapour of water, which is a perfectly impalpable gas,
diffused, even on the clearest days, throughout the atmosphere.
Compared with the great body of the air, the aqueous vapour it
contains is of almost infinitesimal amount, 99.5 out of every 100
parts of the atmosphere being composed of oxygen and nitrogen. In the
absence of experiment, we should never think of ascribing to this
scant and varying constituent any important influence on terrestrial
radiation; and yet its influence is far more potent than that of the
great body of the air.