381 
On Preventing the Decay of Wood . 
consequence to know, that the bark of such timber contains 
much less tan than that of the younger and more succu- 
lent wood; and that this principle, together with the pro- 
per extractive matter, is considerably more abundant in 
the bark of the Leicester or Huntingdon willow, than in 
that of any oak* According to the experiments of Mr. 
Davy, seven pounds and a half of the former will go as 
far in tanning leather as nine or ten pounds of the latter. 
It has however been asserted, that if an oak, or any other 
tree, which is stripped of its bark, be suffered to stand 
two or three years before it is felled, the wood will have 
acquired a very great degree of strength and durability* 
Next, where it is practicable, a current of air should 
be frequently made to pass along the surface of the wood. 
This expedient seems to have been particularly attended 
to by the ingenious architects of our Gothic churches, 
who are said with that view to have left various openings 
in the walls between the two roofs of those edifices. In 
order also to promote evaporation, a certain degree of 
heat, such as that of air heated by the sun or fire, should, 
if possible, be from time to time applied. Cellars them- 
selves ought to have some communication with the out- 
ward air by means of windows and shutters, or trap- 
doors. And that these may be for a short time opened 
in proper weather, so as to have a draught of air, and 
that no very low degree of temperature is necessary for 
the preservation of fermented liquors, provided that tem- 
perature be uniform, is evident from the practicability of 
keeping wine extremely well in cellars which are not 
damp, and in which, therefore, one or both of these cir- 
cumstances must have taken place. 
The destruction of wainscotting may be long deferred 
by keeping in the apartment suitable fires. 
Lastly, the dry-rot may in all cases be infallibly pre- 
vented where it is practicable to cover the surface of the 
