M. Girard on Navigable Canals. 103 
. Of that which is ie rb filtration through the bot- 
we er sides of the canal ; 
3dly. Of that which is neces expended at the locks 
in raising or lowering the 
vaporation is a ae, effect, and which no art can 
counteract : the loss arising from this cause is therefore in- 
evitable. 
Whatever be the nature of the ground through which a 
canal is intended to pass, the loss by filtration may always 
be greatly diminished, or even entirely prevented, by re- 
course to suitable mean 
There remains then Ki expense occasioned by the move- 
‘ments at the locks, and this portion is generally greater than 
the bees by evaporation and filtration together: therefore 
in the -suffici 
water on the most ted point of its direction, 
to supply the uses of that navigation to which it is destined. 
The tmmpossibility of fulfilling “this first condition has often 
prevented the execution of canals, which, could they have 
existed, would have contributed powerfully to the advance- 
ment of agriculture and the prosperity of commerce in cer- 
tain provinces. We have seen o canals which answer 
but imperfectly the object for which they were intended, 
because the water collected for their use could suffice for” 
their wants only during a few months of the year. For this 
reason many engineers and -mechanicians, both i in France 
and England, ‘oi endeavoured to discover some means 
obviating the difficulty of a deficiency of water in navigable 
eanals. Thus the moveable locks of So/ages, the inclined 
lanes of Fulton, the wheel boats of Chapman, the floating 
ecluses 4 flotteur) of Bettancourt, and more recently 
Pnet locks of Congreve, have been successively 
im ed ; but, however Ingenious. these means may ate 
pear in theory, they require in practice, the application 
force with which we may pinay dispense, wherever 
boats can be kept naturally a t, and can circulate aed 
canal without any other sara aed that of passing the 
locks as they were first invented. _ 
On the other hand, eens inventions are practicable taly 
acts canals ; and, where fuel is plenty, the least ex- 
pensive mode of atin a dektiency” of water, is to raise 
