122 M. Girard on Navigable Canals. 
return, but are broken up in Paris, and the materials of 
which they are constructed sold under the name of boat 
wood, 
It would be superfluous to adduce any further proofs in 
support of this opinion. It is easy to conceive that the 
boats which should arrive at Paris from the most elevated 
points of the department of the Ardennes, or of the depart- 
ment of the Cote-d’Or would not return with so weighty 
cargoes as those they should have brought. We may there- 
fore consider it as an established principle that, in a well 
regulated system of internal navigation, the total weight of 
articles which descend the canals will always be much 
. greater than that of the objects which ascend them. 
This principle once admitted, the volume of water neces- 
sary for the navigation of canals will be greatly reduced ; 
and the difficulty of accumulating it in sufficient quantity on 
the summit levels of those canals, will be no longer an 
obstacle to their execution, since, according to our formu- 
le, the lifts of the locks may always be regulated in such 
manner as toexpend but a given quantity of water by the 
passage of boats, and even in case of need, they may be 
nade to raise a certain volume from the lowest to the high- 
est level of the canal. 
To give an example of this manner of proceeding, let us 
suppose that the draft of water of the boats which descend 
a canal be 1" 20°=(3 feet 101 inches nearly,) and that of 
the boats which ascend 30 centimeters (11 4 inches) only. 
Let us suppose further, that the expenditure of water in 
the canal cannot exceed } of the weight of the boats which 
pass the locks in both directions ; substituting these numer- 
ical quantities in our general formula we shall find the prop- 
er weight of the lifts to be 1”, 275¢ (4 feet 21 inches.) 
If, instead of drawing this volume of water from the up- 
yer level, it were necessary to raise the same quantity from 
the lower level to the upper one, the proper lift of the locks 
will be found 0™ 675 (2 feet 2,5 inches.) 
Finally to render the expenditure null, the height of the 
lift would require to be 90 centimetres (2 feet 114 inches.) 
I proposed, in this memoir, to indicate the meansiof sup- 
plying a deficiency of water which might in some instances 
prevent the opening of useful canals; but other, and not 
less Important advantages will naturally accrue from the es- 
