270 Mr. Knight upon the extent of the 
and contraction of timber, when divided in different directions 
relative to the medulla of the tree, and I was not in posses- 
sion 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 pre- 
sence 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 experiments were made upon tim- 
ber 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 above men- 
tioned species of trees, the ash and the beech, were cut in oppo- 
site directions 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 compa- 
rative 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 
