188 S. Webber on Ventilation. 
spare steam for the purpose’ of warming such portions of the 
building as it can readily be conveyed to without much expense, 
the necessary purification of the air being otherwise provided for. 
Such are the principal modes that have been employed for im- 
partin gwarmth to dwelling-houses, with their advantages and 
disadvantages, both as to warming, and as to preserving the purity 
of the air while diffusing heat, with the means necessary for so 
doing while the increase or maintenance of warmth is desirable. 
t this warmth so artificially procured, may become excessive. 
From too large a fire, the presence of too many persons in a room 
where the fire is, and the burning of numerous lights, the air 
may become too warm and impure, and additional ventilation 
and with cooler air may be required. In this case a ventilating 
aperture in the upper part of the chimney is wanted, to permit 
the escape of the warm air from the upper part of the room and 
with it such of the gaseous exhalations, engendered in such cases, 
as are of a light specific gravity. Rooms thérefore used for the 
bearing down with it to the lower part of the room, the impurl- 
ties it might meet with, conveying grateful. refreshment: to the 
lungs, and checking the ascent of impurities from below the 
mouth and nostrils. The very coolness applied to the head is 
one of the best means of preventing the bad effects of the inha- 
lation of air impure from an undue mixture of carbonic acid, 
