104 M. Girard on Navigable Canals. 
from the lower locks to the upper ones, by means of the 
steam engine, the water which has been expended by the 
passage of the boats. 
It would then be rendering an eminent service, and hasten 
the developement of a general system of inland navigation 
in France, if we could point out any means by which the 
expense of water could be diminished, without changing the 
common mode of construction of the locks, which is found- 
ed on so simple a law of Hydrostatics that we must perhaps 
despair of ever being able to substitute any thing more per- 
fect in its stead. 
From the first period of the invention of locks and gates, 
it was easy to calculate the quantity of water necessary to be 
drawn from an upper level or reservoir, to raise or lower a 
boat, when once the difference of levels between two con- 
tiguous locks or basins was given. 
Subsequently, the French engineers agitated the question 
of determining in what manner the expense of water from the 
reservoir of distribution was modified, when several locks were 
placed in immediate succession one after another. ‘The dif- 
ferent suppositions that were made, by changing the state 
of the question, gave rise to many different opinions, of 
which Mr. Gauthey first rendered an account, in a memoir 
published in 1783, among the memoirs of the Academy of 
Dijon, and which is also inserted in the 3d Vol. of his 
works. 
The engineers of the canal of Languedoc, who were 
deeply interested in the exact appreciation of the expence 
of the dividing reservoirs of thatcanal, and who had every . 
facility for repeating the experiments, in the two hypotheses 
of single locks, and of several locks contiguous to each oth- 
er, occupied themselves specially with the subject, and gave 
divers solutions of the problems, as may be seen in a me- 
moir of Mr. Ducros, inspector general of Civil Engineering 
(Ponts et Chaussees,) published in the year IX. After 
having pointed out, as Mr. Gauthey had done before him, 
the order in which the boats which ascend and descend a 
canal, should succeed each other in order to occasion no 
useless waste of water, Mr. Ducros gave some formule to 
express the expense of water on the passage of a boat, ei- 
ther in ascending or descending through any number of ad- 
joining locks ; General Andréossy, author of the History of 
