823 
On Preventing the Decay of Wood . 
the inside of our windows during the heat of a sum- 
mer’s day ; nor is there any condensation of moisture on 
the outside of a glass of cold water fresh drawn from 
the well, or of a bottle out of a cellar, when either is 
brought into the open frosty air. 
These circumstances will explain many appearances, 
by which, for want of due examination, we are often 
greatly puzzled. We are frequently mortified by seeing 
in our houses, especially in the country, the walls be- 
come stained, or the paper separated and hanging down, 
and often perishing; and as this usually happens on the 
side or corner which is most exposed to the weather, we 
conclude that the damp comes through the wall, and 
tax our faculties to the utmost, in order to prevent this 
penetration. The measures which we employ some- 
times succeed. But it often happens, that casing, and 
plaistering, and painting the devoted angle fails; and 
then, as the last resource, we take off the paper and at 
tach it to canvass at the distance of one or more inches 
from the wall, and thus, for the present at least, effect 
the desired purpose. Now in this case it is just as ab- 
surd to suppose, that the wet comes through the wall, as 
that it comes through the glass window in a frosty day, 
or the glass or bottle from the well or cellar. The fact 
is, that in an exposed house, and more especially on the 
most exposed corner of a room seldom warmed by fire, 
the inner surface of the wall, by the continuance of frost, 
is become of a very low temperature, like the air within 
the room itself. So long as this state of equal tempera- 
ture between the wall and internal air continues, or if the 
wall is warmer than that air, it is obvious that the vapour 
which is mixed with the air cannot part with any heat to 
the wall, and therefore will not undergo condensation; 
just as no dampness appears on our windows during a 
hot day in summer. But if a thaw comes on, and the air 
