M. P. S. Girard on Navigable Canals. 305 
Whatever may be the rise of water in each of the consec- 
utive levels of a navigable canal, it is evident thatthe whole 
body of water which constitutes this augmentation, and is 
spread throughout the extent of them all, is taken from the 
lower level, or rather, from the river in which the canal ter- 
minates. ¢ 
If, by the effect of a first double passage through all the 
locks of a canal, the surfaces of its different levels become 
elevated, the primitive falls of its locks will be altered, 
and we must calculate, assuming the falls as thus modified, 
what will be the effect of a second double passage; and so 
of a third, a fourth &c. whence we see that after a certain 
number of passages of boats the rise of water on any given 
level will depend not only on the rise of water on all the 
levels above the one under consideration ; but also on the 
number of double passages which shall already have taken 
Se So that the expression of the rise om any gi 
evel, becomes so much the more complicated as that level 
is farther removed from the reservoir of the summit level, 
and as the number of boats which have already passed be- 
of the ground where the canal is made, and according to 
extent of its levels, it follows that the rise of water on 
each level should be made to vary to suit the permeability 
of the ground, or such other considerations as experience 
water in each level equally, or, which comes to the same 
thing, that the water raised from the lower level should be 
divided among the higher levels in proportion to their re- 
spective lengths. ; 
Our formula, applied to this particular case, shew that 
the same relation exists between the length of a level and 
Vou. VII.—No. 2. 39 . 
