M. P. S. Girard on Navigable Canals. 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 eifecting this double pas- 

 sage. 



From that equation I deduced the immediate conse- 

 quence that the expenditure of water, at the passage of a 

 lock, 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, oj equal 

 to that difference ; whence it is easy to conclude, not only 

 that the expenditure of water maj' 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 level. 



It is true that to produce the latter 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 transport, and 

 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 difficulty of collecting a large vol- 

 ume of water in the culminating point, will no longer he 

 an obstacle to their undertaking. 



The consequences of our new theory are, as we see, 

 highly important ; and if, in order to render all their im- 

 portance, as it were palpable, we were permitted to bor- 

 row the expressions which have been elsewhere urged as 

 arguments against it, we should say : "'that it is question of 

 nothing less than to change the rules laid down for canals, to 

 proscribe the present dimensions of locks, and to prove that 

 the practice hitherto adopted has tended to deprive com- 

 merce of a portion of its natural activity, and to prevent, in 

 many countries, an augmentation of national wealth." 



A system of internal navigation susceptible of extending 

 its ramifications through many parts of countries which na- 

 ture seemed not to have destined to enjoy the advantages 

 of this species of communicatio.'i, is an object wort[iy of 

 the most profound meditation, and discussion. Generally 

 received ideas, and deep rooted prejudices may oppose its 



