M. P. S. Girard on Navigable Cangl. 287 
orous equation which expresses the relation between the 
lift of any lock whatever, the draft of water of the boats 
which ascend that lock, that of those which descend, and 
the volume of water expended in effecting this double pas- 
sage. 
From that equation I deduced the immediate conse- 
quence that the expenditure of water, at the passage of a 
ock, is positive, negative, or null, according as the lift of 
that lock is greater or less than the difference of draft of 
the boats which descend and those which ascend, 04 equal 
to that difference ; whence it is easy to conclude, not only 
that the expenditure of water may be rendered as small as 
we please, but that it is possible to raise a certain. portion 
of water from an inferior to a superior contiguous | vel. 
itis true that to produce the Jatter effect the following 
condition is necessary : that the draft of water of the boats 
which descend should be greater than that of the ascending 
ones ; but it is only necessary to consider the nature of the 
productions which the canals are destined to transportyand 
the situations whence those productions are derived, and 
where they are ordinarily consumed, to be convinced that 
th:s condition is almost always fulfilled —Whence, the con- 
sumption of water in navigable canals will undergo very 
great reductions ; and the difficuity of collecting a large vol- 
ume of water in the cu/minating. point, will no longer be 
an obstacle to their undertaking. ep 
stined to enjoy the advantages 
ture seemed not to have destin enjoy aaa ot 
the most profound meditation, and discussion. Generally 
