M. P. S. Girard on Navigable Canals. 313 



serious inconveniencies into which men have been led from 

 an ignorance of the true principles. 



These inconveniences exist in the canal de Briare, the 

 oldest canal in France and the most general!}' known. 



The number of boats which descended this canal in 1819 

 was 3380. These boats were of different dimensions ; but 

 we can suppose as a mean term that, loaded, their draft of 

 water was 0.66 metres (26^ inches ;) thej are 24 metres 

 (79 feet) long, and 3.50 metres (1 1| feet) wide. 



The mean cargo of one of these boats, is consequently 

 about fifty tons. 



The whole weight of articles brought to Paris, on this 

 canal, during the year 1819, was, therefore, about 170,000 

 tons. 



The far greater portion of these boats were demolished 

 at Paris, and those that ascend the canal go empty. At all 

 events it is certain that the goods transported from the 

 Seine to the Loire, do not weigh one hundredth part so 

 much as those which come from the Loire to the Seine. 



The whole length of the canal de Briare, from the di- 

 viding pomt to the River Loing, is 34582 metres (6934. J 

 rods, or 21.67 miles) ; its descent, which is 78.74 metres 

 (258. i feet,) is surmounted by 27 locks, the lift of some of 

 which is near 4 metres (13y/o feet). 



It is a long time since it has been observed that there 

 was a great loss of water, occasioned by the passage 

 through the locks where the lift and fall was so considera- 

 ble, and so disproportionate to the draft of water of the 

 boats destined to pass through them. Rut, such is the state 

 ■of things : in order to appreciate the consequences, let us 

 first determine what quantity of water would be absolutely 

 necessary for the circulation of 170,000 tons of merchan- 

 dize on the canal de Briare. 



Now it isevideut thatif the numberof locks had been quad- 

 rupled, their mean lift would have been reduced to about 75 

 centimetres, (2yVo ^eet ;) and if the draft of water of the 

 loaded boats had been carried to 1//^ metres (4,yVo ^eet,) 

 it is also evident that in consequence of the diminution in- 

 the lift, and the augmentation of the draft of the boats, the 

 1350 boats, which together would carry as much as the 

 3380 boats which descended to the Seine in 1819, that is 

 to say, which would displace the same quantity of 170.000 

 tons of water, would elevate, by their descent, the half of 



VoL.VII.— No. 2. 40 



