.

The _direct_ influence of rain on man is not very marked in this country,
except by giving moisture to the air by evaporation from the ground and
from vegetable life, and by altering the level of ground water. This is a
subject almost overlooked by the public, and it is therefore as well that
it should be known that when ground water has a level persistently less
than five feet from the surface of the soil, the locality is usually
unhealthy, and should not, if possible, be selected for a residence.
Fluctuations in the level of ground water, especially if great and sudden,
generally cause ill-health among the residents. Thus, Dr. Buchanan in his
reports to the Privy Council in 1866-1867, showed that consumption (using
the word in its most extended sense) is more prevalent in damp than on dry
soils, and numerous reports of medical officers of health, and others,
which have been published since then, show that an effective drainage of
the land, and consequent carrying away of the ground water, has been
followed by a diminution of these diseases.

Varying amounts of moisture in the air materially affect the health and
comfort of man. In this country, however, it is not only the absolute but
the relative proportions of aerial moisture which materially influence
mankind. The quantity of aqueous vapor that a cubic foot of air can hold
in suspension, when it is saturated, varies very much with the
temperature. Thus at 40 degrees Fahr. it will hold 2.86 grains of water;
at 50 degrees, 4.10 grains; at 60 degrees, 5.77 grains; at 70 degrees,
8.01 grains; and at 90 degrees as much as 14.85 grains. If saturation be
represented by 100, more rapid evaporation from the skin will take place
at 70 degrees, and 75 per cent. of saturation, than at 60 degrees when
saturated, although the absolute quantity of moisture in the air is
greater at the first named temperature than at the latter. As regards the
lungs, however, the case is different, as the air breathed out is, if the
respirations be regular and fairly deep, completely saturated with
moisture at the temperature of the body. In cold climates the amount of
moisture and of the effete matters given off from the lungs in the expired
air is much greater than in hot climates, and the body is also cooled by
the evaporation of water in the form of aqueous vapor. Moist air is a
better conductor of heat than dry air, which accounts for much of the
discomfort felt in winter when a thaw takes