A complete handbook for the sanitary troops of the U S army and navy . mportant agent is gravity. Equal volumes of air of thesame temperature and under the same pressure have equal weights;now if one of the volumes is heated it expands and becomes lighter,and being surrounded by heavier air, rises, or rather is forced up, AIR AND VENTILATION 345 by the sinking of the heavier air, and thus currents are the air in a room is heated by fire, hghts, or even the humanbody, it becomes Hghter, and the heavier outside air forces itself inthrough all the openings and crevices, at the same
A complete handbook for the sanitary troops of the U S army and navy . mportant agent is gravity. Equal volumes of air of thesame temperature and under the same pressure have equal weights;now if one of the volumes is heated it expands and becomes lighter,and being surrounded by heavier air, rises, or rather is forced up, AIR AND VENTILATION 345 by the sinking of the heavier air, and thus currents are the air in a room is heated by fire, hghts, or even the humanbody, it becomes Hghter, and the heavier outside air forces itself inthrough all the openings and crevices, at the same time forcing thelighter air out, thus effecting a certain amount of ventilation. Unequal temperatures in masses of air outside dwellings give riseto winds, and winds aid ventilation in two ways: First, by perflation,or blowing through a room when the windows are open, and second,by aspiration when it blows across chimneys or flues. Ventilation of a dwelling is said to be either natural or mechanical;natural when we trust to the forces of nature, merely providing the. ?Flo. 225. —Heating and Wntilation by Jacketed Stove. necessary entrance and exit openings, together with heat if required :mechanical when the air is forced in or drawn out by fans or othermechanical means. In any system it is to remember that it requires twoopenings to secure ventilation; if only one opening is provided, theincoming and outgoing currents interfere with each other and venti-lation fails. This is well illustrated by the familiar experiment ofburning a candle inside of an unstoppered bottle; if the openinginto the bottle is divided into two parts by a partition, the candlewill burn, because the air currents pass up one side of the partition 346 HYGIENE. POST AxND CAMP SANITATION and down the other without interference; if the partition is removedthe hght goes out. Ventilation in in hot chmates is largely a matter of theaction of winds, because the temperature of inside and out
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