ox HTDROSTATIC INSTRUMENTS, AND HYDRAULIC ARCHITECTURE. 31J 



If the side of a canal gives way, it is sometimes of consequence to prevent, 

 as much as possible, theescape of the water. For this purpose it is usual to 

 have doors or valves in various parts of the canal, which, when the water is 

 at rest, lie nearly flat at the bottom ; but when it begins to run over them, 

 with a considerable velocity, they are raised by its force, and put a stop to 

 its motion. 



The utility of the introduction of canals into a commercial country may 

 be estimated in some measure by the effect of the same labour, employed in. 

 removing weights by land carriage and by water. Thus, a single horse can 

 scarcely dra\r more than a ton weight on the best road, but on a canal, the 

 same horse can draw a boat of 30 tons at the same rate. , 



The construction of piers and quays, and the management of harbours, are 

 also important departments of hydraulic architecture ; it often happens that 

 besides the application of the general principles of mechanics and hydrostatics 

 to tliese purposes, the peculiar circumstances of the case may indicate to an 

 ingenious artist a mode of performing the required work in an effectual and 

 economical manner. We may find a good example of such an arrangement, in 

 the account given, by Mr. Smeaton, of the method which he adopted for the 

 improvement of the port of Ramsgate, and which indeed resembles some that 

 had been before employed in similar cases : by forming a larg-e excavation, 

 which is furnished with flood gates, and is constantly filled at high water, 

 he has procured a number of artificial torrents, which escape through the 

 sluices, and become powerful agents for carrying away the matter deposited by 

 the sea, and tending to impede the navigation of the harbour. 



