aa_— 
M. Girard on Navigable Canals. 115 
ing the lift of the locks. The principles on which this con- 
clusion is founded are evident ; the calculations which jus- 
tify it are simple and easily verified. And yet it appears to 
ve hitherto escaped the attention of engineers who have 
occupied themselves in projecting or in constructing canals. 
It is in the natural progress of our mind, and in the slowness 
with which certain branches of knowledge are propagated, 
that we must look for the cause of the seeming abandon- 
ment in which the questions which form the object of the 
present memoir have remained. 
The first inventors of canal locks, as well as those who 
first constructed them, captivated as they must have been 
by the effectof this i ingenious eseseemeradie attributed to it so 
much the more merit greater diffi 
culty = a osts: step. 
vieweasansd; hie iat Mocks: were constructed in 
the Venetian States, ona aah derived from thé > Brenta, 
no apprehensions need have been entertained of a want of 
wider, since the canal was supplied by a river; besides, to 
make any exact calculations of the expense of water at the 
ero of the locks, it was necessary that the Jeti sci- 
s should have progressed farther than they had done 
before the days of Galileo, and cciene imperfect notions then 
of those sciences should have been more gene 
It is easier to i what has bee Pulriedy- oneris’ hy: 
draulic: ‘constructions, “Aliens to imptove them, or even to ac- 
count for certain practices which usage seems to” eine al 
proved and consecrated. yt te 
Every one knows that one of rhepeiatapks obutaelés:to 
the execation of the canal of Languedoc, was the difficulty 
¢ on the summit level a quantity of water sufli- 
cient forthe se service of the locks, and the navigation of the 
mise the water that could” be procured. = Ea eases 
gi ie we 
mA 
da Gane (0: too much 
