lassitude felt in warm climates is, that the air expanding with the
heat, while the lungs remain of the same capacity, they must take in a
smaller quantity by _weight_, though the same by _measure_, of oxygen,
the supporter of life; but if, in addition to the air being rarefied,
it be also still further distended by the vapour of water being mixed
with it, it is evident that a certain number of cubic inches by
measure, or the lungs full, will contain a less weight of oxygen than
ever; so little, indeed, that life can barely be supported; and we
need not wonder at persons lying down almost powerless in the hot and
damp atmosphere, and gasping for breath. Hence we see that any method
of cooling the air for Indians, instead of adding moisture, should
rather take it out of the air, so as to make oxygen predominate as
much as possible in the combined draught of oxygen, azote, and a
certain quantity of the vapour of water, which will always be present;
and hardly any plan could be more pernicious than the favourite though
dreaded one by those who have watched its results--of the wet mats.
Cold air--that is, air in which the thermometer actually stands at a
low reading--by reason of its density, gives us oxygen, the food of
the lungs, in a compressed and concentrated form; and men can
accordingly do much work upon it. But air which is merely cold to the
feelings--air in which the thermometer stands high, but which merely
gives us one of the external sensations of coolness--on being made by
a punkah, or any other mere blowing machine, to move rapidly over our
skin--or on being charged with watery vapour, or on being contrasted
with previous excessive heat--such air must, nevertheless, be rarefied
to the full extent indicated by the mercurial thermometer, and give
us, therefore, our supply of vital oxygen in a very diluted form, and
of a meagre, unsupporting, and unsatisfying consistence.... The _sine
quâ non_, therefore, for healthy and robust life in tropical
countries, is air cold and dry--cold to the thermometer and dry to the