ig6 Relation of Moisture in Air [April, 
living rooms in mid-winter ; while the American shivers with 
cold at 70°, and is not over-warmed at 7 6°, in the apartments 
of his own dwelling, although clad in the thickest of under- 
clothing. Investigation, however, shows that the deprivation 
of heat from the person is more due to evaporation from the 
lungs or throat, and from the skin, than from heat otherwise 
dispersed, whether carried off by the breath, imparted to the 
air, or radiated to surrounding objetfts. And further investi- 
gation will show that the hygrometric state of the air has so 
much effedt in inducing or retarding evaporation as to make 
56° F. in the West and South of England, in Ireland, and in 
Normandy, sensibly as warm as 8o° in Canada or Minnesota 
at the same season. A brief statement of the difference of 
climatic condition of England and of America may show 
why we cannot import English theories of ventilation and 
heating, and apply them at once, without modification, to 
American residences. The English climate affords nearly 
eight months in every year when the thermometer ranges 
between 40° and 6o° in the shade, with a dew-point so high 
that it is a pleasure to exercise in the invigorating air ; one 
month of 6o° to 8o° ; and three months from 25°to 50° ; there 
being no term, except a part of the one month of heat reaching 
to 8o°, when any person cannot, with suitable clothing, enjoy 
the open air. While in America there is scarcely one month 
(or thirty days) out of the year having an average temperature 
of 50° to 75 0 (which temperatures, from the difference of dew- 
point, correspond sensibly with 40° to 6o° in England) ; and 
there are three months of 7 5 0 to go° ; three months of 30° to 
50° ; and five months of excessive variation of temperature 
of from o° to 50°. During the three hot months, and also 
during most of the five cold, open-air exercise to those whose 
avocations are within doors is, if not impossible, at least 
very uncomfortable, however clad or covered. Anyone who 
is called upon to endure the fervid summer heat, or who can 
habituate himself to the inclemencies of our ardtic winter, 
will not suffer great discomfort, nor experience much injury 
to his health -therefrom ; but the weak and tender — the mer- 
chant from his counting-house, the student from his closet, 
the workman from the shop, the women and children of the 
house — cannot acquire the endurance or the habit, and must 
shelter and protedf themselves. 
This preamble to the subjedf has been intended to impress 
the fadt that its consideration must be on its own merits, and 
not through the light thrown upon it by general writers, that 
its investigation shall be original from physiological consider- 
ations, and not based upon authorities. 
