488 Upon the Extent of the Expansion and Contraction 
directions relative to the medulla of the tree, and I was not 
in possession of any fact which enabled me to prove the existence 
of any such power, in a state of action, in the living tree. But 
experiments, which I have made at different subsequent periods, 
have afforded very satisfactory evidence of the presence of this 
power in a state of action in living trees, and have also enabled 
me to ascertain some facts, which appear interesting, and likely 
to prove useful in directing the proper mode of application of 
wood for various purposes, in which it is important that it should 
permanently retain its primary extent and form, These expe- 
riments were made upon timber of many different kinds; but as 
the results were all very nearly the same, I shall confine myself to 
those made upon the oak, the ash, the beech, and poplar. 
Some thin boards of the wood of two of the abovementioned 
species of trees, the ash and the beech, were cut in opposite di- 
rections relative to their medulla, so that the convergent cellular. 
processes crossed the centre of the surfaces of some of them at 
right angles, and lay parallel with the surfaces of others; by 
which means I became enabled to mark the comparative extent 
of their expansion and contraction when they were subjected to 
various degrees of heat and moisture. Both were placed under 
perfectly similar circumstances in a warm room, where those 
which had been formed by cutting across the convergent cellular 
processes soon changed their form very considerably, the one 
side becoming hollow, and the other raised; and, in drying, these 
contracted nearly fourteen per cent. relative to their breadth. 
The others retained, with very little variation, their primary 
form, and did not contract more than three and a half per cent, 
in drying. Both were, subsequently, several times subjected to 
various degrees of temperature and moisture, gad each expanded 
nearly in the same degree that it had contracted, the form of the 
one remaining very nearly permanent, and that of the other con- 
stantly changing. 
_ A beech and an ash tree, each somewhat exceeding twenty 
inches in diameter, were felled in the end of January, (at which 
time the buds of beth had become sensibly enlarged,) and a trans- 
verse section of about an inch in thickness, and necessarily of a 
circular form, was immediately cut off from the trunk of each, 
near its base. An incision was then attempted to be made with 
a saw from the bark to the medulla, directly in the line of the 
convergent cellular processes, with the expectation that these, on 
each side, would expand, and impede the . ction of the saw. The 
result was just what I had anticipated, and long before the saw 
approached near the medulla, it became so strongly compressed 
that my assistant could scarcely move it. A much thinner saw, 
which I had in readiness, was then employed ; and the incision, 
which 
