[ 2 *7 1 



door, for I know not what other name to 

 give it. It is upon the fame principle as 

 that at the mouth of the fubterranean paf- 

 fage, in which the boats unlade in Cajile- 

 Jield. The contrivance and defign of thefe 

 doors are admirable ; but as many of them 

 will occur in this tour of the navigation, it 

 will not be improper to explain the con- 

 struction of them here. 



In the fketch, Plate V. Fig. 4. A repre- 

 fents one fide of the chanel of the canal, be- 

 ing walled; B, is the floor of it; C, C, are 

 two doors, fixed in the pofition they appear 

 in, and turning on hinges at bottom, d,d,d,d. 

 The doors have a freedom of riling, but can- 

 not fall lower ; now it is obvious from this, 

 that in cafe the bank A, breaks, and the wa- 

 ter rufhes out of the breach, the decreafe of 

 preflure on the doors C, C, will raife them 

 up at once to e, e, (where they will be fixed 

 againit projecting irons made for that pur- 

 pofe,) as the water at F, F, will then natu- 

 rally force them up. The confequence of 

 which is, the lofing no more than the wa- 

 ter contained between the doors ; and if the 

 bank fhould break at F, yet the quantity of 

 water loft would be but trifling. I have 

 thrown the doors near one another, for your 

 fully underftanding the principle on which 

 they are deligned ; but in the canal they are 

 are at a diftance from each other in divers 

 places. The flopping the lofs of water is of 



great 



