of Ventilating and Warming Buildings, 28S 
l)y heat, we must either take a greater quantity into the lungs 
at once, or breathe oftener in the same time, to obtain that quan- 
tity of oxygen our system has been accustomed to absorb. But 
the diminished proportion of oxygen, in a given bulk of air, is 
not the only cause of our feeling oppressed in heated air ; for, 
by heating air we increase its power of abstracting moisture from, 
us. If a r(X)m be warmed by radiant heat alone, the solid mat- 
ters in the room are warmed, without heating the air to the same 
degree, because radiant heat, passing through the air, does not 
materially increase its temperature. 
The impressions of radiant heat diminish as the squares of 
the distance from the fire, and consequently extend, so as to be 
effective, to a small distance only. This suggests the expedient 
of employing a moTeable screen, to receive the impressions of 
heat, and protect the family circle from the influx of cold air, 
from the distant parts of the. room. Such a screen may be con- 
tracted or expanded, according as the weather is more or less 
severe, and entirely removed in summer. The Chinese or Ja- 
penese screen is partially used for this purpose, but the taste of 
our countrywomen is capable of giving it more appropriate or- 
naments, and of rendering it as interesting as it is useful. 
The lively and cheerful blaze, and genial beat, of an open 
fire, is not, however, to be obtained at a small expence; and, 
by other methods, the same room may be warmed by one-third 
of the fuel required by an open fire, These methods I shall 
proceed to explain, noticing every variety that is not objection- 
able, by being injurious to health. 
In the methods I am about to describe, warmth is communi- 
cated by contact ; and, since the heat is ultimately communi- 
cate to the air of the place which it is the object to warm, it 
is of the utmost importance that that air should not be injured 
by the hotness of the surface from which it obtains heat The 
fact that air receives no injury from a surface of the tempera- 
ture of boiling water, is very well ascertained ; and, perhaps,' it 
may pass over a surface, heated to S00°, without material in- “ 
j-ury, but not when the temperature is higher. Air which has 
passed over red-hot iron, or red-hot brick, acquires a disagree- 
able odour, and, in respiration, produces a harsh dry sensation 
in the. organs, and a tendency to coughs* Air which has passed. 
s 2 
