314 M. P. S. Girard onMnvigable Canals', 



this volume of water from the River Loing to the dividing 

 level ; which would have augmented in so much the quan- 

 tity of water in the reservoir of the culminating level which 

 is destined to supply the navigation of the other branch of 

 the canal, from that level to the Loire. 



Supposing, as we now do, an importation from that river to 

 the Seine, without reciprocity, it is indispensable to provide 

 for the expense of water in the ascending navigation of that 

 branch of the canal. 



Its whole length is 32231 metres (6407t^'o- rods, or verj 

 nearly 20 miles,) the whole fall is SSyVo metres, (124//^ 

 feet,) and is overcome by 12 locks of different lifts. 



By augmenting the number of its locks so that the lift of 

 each should be no more than 75 centimetres (2yYo feet,) 

 equal to what we have supposed them on the other part of 

 the canal, there would be expended, to raise the 170,000 

 tons of merchandize : 



1st. — 85,000 tons of water, equivalent to filling the ba- 

 sins of the locks ; 



2ndly. — 170,000 tons of water, representing the volume 

 of water displaced by the whole of the cargoes. 



The ascending navigation from the Loire to the culmina- 

 ting point of the canal de Briare, would therefore require 

 an expense of 255,000 tons of water, which would necessa- 

 rily descend from the reservoir on the summit level to the 

 Loire. 



But we have seen that the descent of the same mer- 

 chandize, on the opposite side, elevated to the reservoir 

 85,000 tons of water drawn from the river Loing ; there 

 would therefore only require to be furnished from the 

 ponds and feeders, 170.000 to 200,000 tons of water, or 

 thereabouts; so that abstracting the absorptions and evap- 

 orations, that is the minimum quantity of water, indispensa- 

 ble for the annual supply of the navigation of the canal de 

 Briare, and the volume of which it would be necessary to 

 be able to dispose, on the dividing level. 



Let us now examine the quantity of water annually ex- 

 pended to maintain that navigation. 



The ponds indicated in the work of M. de Lalande, con- 

 tain G,080,000 tons of water, and are reserved for the sup- 

 ply of the canal de Briare. 



If we suppose, according to an evaluation generally admit- 

 ted, and which would perhaps be here too high, that the 



