800 
On Preventing the Decay of Wood . 
built by Richard XT, in 1397; and the more extraordina^ 
ry instance quoted by Dr. Darwin, in his ingenious 
work, the Phytologia, of the gates of the old Saint Peter’s 
church, in Rome, which were said to have continued 
without rotting, from the time of the emperor Constan- 
tine to that of pope Eugene IV, a period of eleven hun- 
dred years. On the other hand, wood will remain for 
ages with little change, when continually immersed in 
water, or even when deeply buried in the earth; as in 
the piles and buttresses of bridges, and in various mo^ 
rasses. 'these latter facts seem to show, that, if the ac- 
cess of atmospherical air is not necessary to the decay of 
wood, it is, at least, highly conducive to it. 
In posts fixed in the ground and exposed to the wea- 
ther, we constantly find that part soonest decay, which is 
just above or within the ground. So also where there is 
an accidental hole in an exposed surface, or any artifi- 
cial cavity, as in a mortice and tenon, or the part where 
pales nearly touch the rails on which they are nailed, 
there the wood universally begins first to moulder away. 
The same thing happens with regard to horizontal rails 
themselves, which, when made of the same materials, 
rot much sooner than the pales which they support. 
These facts are very easily explained. They clearly show, 
that the great cause of decay is the constant action of water 
aided by air, which most affects those points, where it 
is most retained, but has less operation, where, as in the 
perpendicular pales, it chiefly runs off by its own gravity, 
so that the little which remains is easily and quickly ab- 
stracted by the co-operating power of the sun and wind. 
The change which I am describing is the consequence 
of putrefactive fermentation; a chemical operation, in 
which the component parts of the wood form new com- 
binations among themselves, and with the water which is 
essential to the process. The precise nature of these 
