M. P. S. Girard on Navigable Canals. 314 
evaporation and the filtrations absorb one fifth part of this 
reserve, there will remain 4,864,000 tons of water for the 
purposes of navigation alone, 
By the application of our principles to the lift of the 
locks, and the draft of water of the boats, we found that the 
expense of water necessary for that same navigation, may be 
reduced to 200,000 tons; whence it appears that at least 
37 of the water specially reserved forthe use of this canal are 
consumed in pure loss, and yet, the navigation on this canal 
is ofien interrupted for several months in the year for thé 
want of water. 
This imperfection of the canal de Briare, inevitable 
consequence of the excessive lift of its locks, compared 
with the small draft of water of the boats which frequent 
it, is also common. to some other canals of more recent 
construction. “~ sik dics E af 
The relation between the lift of the locks of a navigable 
canal, and the draft of water of the boats which navigate it 
ascending and descending through those locks, constitutes 
as it were the regime of that canal ; and, this regime is es- 
sentially variable. It depends not only on the disposable 
volume of water in different localities, but also on the terri- 
torial or manufacturing resources of the countries th h 
which it passes, and on the nature of importations into 
these countries. : sre sores? add earl )-2 
Thus, in passing a canal in a direction where it could re- 
