%28 On Preventing the Decay of Wood . 
The same process obtains in all other cases. When 
ever the wood is cooler than the air which it touches, the 
vapour is condensed upon it; and being exposed to no 
new heat or current of air sufficient again to evaporate it, 
remains till another tit of condensation affords a new 
supply. 
Thus the process of corrosion and decomposition is 
continually supported till the wood moulders away. 
The term dry-rot is, therefore, so far from being ex^ 
pressive of the real fact, that decay proceeds under these 
circumstances more quickly than in the open air, precise- 
ly because the wood is more constantly and uniformly 
wet; just as the lower parts of posts and rails, and any 
cavities in timber exposed to the weather, rot sooner than 
those parts which readily and speedily dry. 
The smell which we perceive on going into vaults or 
cellars, where this process is going on, arises partly from 
the extrication of certain gases, mingled perhaps with 
some volatile oil, and partly from the effluvia of those ve- 
getable substances, which have already been said to grow 
on it ; and which, though they begin merely because the 
decayed wood is their proper soil, yet afterward tend 
probably to the more speedy decomposition of the wood 
itself. They cannot, however, with more propriety be 
said to be the cause of the dry-rot, than the white clover, 
which appears on certain lands after a top-dressing of 
coal-ashes, can be said to have produced the soil on 
which it flourished. 
I have remarked above, that sometimes only a parti- 
cular sort or sample of timber has in certain situations 
rotted, while another piece has continued for a great 
length of time perfectly sound. Hence persons have 
been deceived, and been disposed to attribute the dry-rot 
solely and universally to some original peculiarity in the 
wood itself. Hr. Darwin explains this fact by telling us, 
