“U. Girard on Navigable Canals. 119 
stantly, pice # be the degree of activity of navigation, 
the lift of each lock must be proportioned to the sum of the 
volumes of water furnished by the summit level and by all 
the collateral feeders above the lock in question, after de- 
ducting therefrom the sum of the losses by evaporation and 
filtration throughout the same extent; now as the quanti- 
ues of water acquired and lost in a given length of canal, 
are exceedingly variable according to the localities (and the 
seasons °) it follows that the equality of lift recommended to 
be established in all the locks of a canal, is reduced toa 
simple rule of practice that is not justified by any theory, 
and which can find no reasonable application armies under 
a concurrence of circumstances rarely to be met wi 
e have just oh to what laws the lis of the 
fae 2 a navigable canal should. be made to vary in a given 
case, abstracting, as. we have the consideration of a 
difference in the draft of water of the boats. It would. be 
easy, taking that difference into account, to deduce from 
our formule the law of variability of those lifts in similar 
circumstances. The simplicity of these calculations ren- 
ders their application here unnecessary. 
The quantity of dynamical action, or active force expend- 
ed in in ps the lect has not yet fixed the attention 
Enero ooh ap I shall now proceed to demonstrate in 
RS oe EA SME e may lead 
xp to 
+ ak ne PES EE ick: os 
the em 
I shall begin by recalling this inpantestable- Bye “that 
active forces and dynamical actions, from whatever source 
derived, and in whatever manner they are disposed of, can 
always represent the useful effect of some machine. The 
economy of these forces, by the adoption oFsve vet meting 
eal s; will therefore leave a greater 
be disposed of; for example, if we regulate in a proper 
manner the rise and. on “the locks of a i CaN See 
the riaant: 
the use of mills on the banks of the cael, orto ay ee 
useful purpose. pe Pag 
Int 
> second ana, = 
expense of active force, indisp i : 
sage of a lock, in raising | one. boat and lowe ng 2 er, is 
alas: proporlipnaal to se raquaee ab ote f Bech, lock, 
