98 
STRUCTURE OF WOOD, &C. 
Quantities of From a comparison of these results it appears, that these 
^ahle'matfer W00( ^ s > w ^en exposed to the air at a temperature of 45° F. 
in wood. contain twice the quantity of water, that they do when the 
temperature of the air is at 60° F. But it is necessary that 
the wood be cut into very thin shavings, to enable it to become 
suddenly in equilibrio with the air, conformably to its quality of 
an hygrometric body ; otherwise the state of the air may 
change, and that very frequently, before its humidity or dry- 
ness can have had sufficient opportunity to produce all its effect 
upon the wood. 
To discover what is termed the medium dryness of any species 
of wood, in our climate, it is requisite that we be acquainted 
with the quantity of water contained in the wood, every day of 
the year, and even in every hour and every minute, which is 
obviously impossible : but there is another method to be pur- 
sued in this enquiry, much less laborious, and which will lead to 
results as satisfactory as the nature of the subject will admit. 
As a very large piece of wood, a large beam for instance, 
dries so very gradually in the air, as not to attain a state of per- 
fect dryness in less than 50 or 60 years, it is sufficient to exa- 
mine the interior of such a beam, after having been sheltered 
for 80 or 100 years from the rain, to discover the state of such 
part of the wood as may still be considered sound. 
In pulling down old houses, we meet with beams proper for 
the present enquiry. 
An old castle in my neighbourhood being pulled down, I had 
an opportunity of examining the interior of a large oaken beam, 
which had, without doubt, been there more than 150 years, and 
as it formed part of the timbers of the edifice, had been secured 
from the rains. 
A piece of this wood, in a bigli state of preservation, after it 
had been planed by tbe workman, was accurately vyeighed, and 
then plunged into water, to ascertain its specific gravity. It 
weighed 75 '05 grammes, and displaced ! LO grammes of water, 
at rhe temperature of 6l° F. $ its specific gravity, therefore, 
was 68227, and a cubic inch weighed 13*53 grammes. 
Forty shavings of this wood weighed 1 ] '4 grammes, which 
were reduced to 10 2 grammes, when they had been tho- 
roughly dried in the stove. 
Hence 
