314 M. P. S. Girard on Navigable Canals, 
this volume of water from the River Loing to the dividing 
level ; which would have augmented in so mach 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. 
upposing, 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 (6407;'5 rods, or very 
nearly 20 miles,) the whole fall is 38.,3, metres, (1247s 
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 (2,4,%5 feet;) 
equal to what we have supposed them on the other part 
the canal, there would be expended, to raise the 170,000 
tons of merchandize* 
I1st.—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 
ire. - 
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, oF 
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 t0 _ 
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 6,080,000 tons of water, and are reserved for the sup- 
Ps the canal de Briare. 
we ccordi 
ppose, g to an evaluation generally admit- 
ted, and which would perhaps be here too high, that the 
