IM'KF/S CANAL To Till-; MK1ISKY. 



875 



On the <lav following Brindlrv's examination before 

 the ( 1 ninniittee nn the Duke's hill, that is, on the 18th 



;is a means (A carrying navigations 

 through an uneven country, and 

 raising the boats I'ruin one water level 

 to a not her, or rice v<-rsfi. The lock 

 is a ehainlx-r formed of masonry, 

 occupying the bed of the canal Avhere 

 the diU'erenee of level is to be over- 

 eoine. It is provided with two pairs 

 of gates, one at each end ; and the 

 chamber is so contrived that the level 

 of the water which it contains may be 

 made to coincide with either the 

 higher level above, or the lower level 

 below it. The following diagrams 

 will explain the form and construction 

 of the luck. A represents what is 

 called the upper pond, B the lower, C 

 is the left wall, and DD side culverts. 

 When the gates at the lower end of 

 the chamber (F) are opened, and those 

 at the upper end (F) are closed, the 

 water in the chamber will stand at 

 the lower level of the canal; but 

 when the lower gates are closed, and 

 the upper gates are opened, the water 

 will naturally coincide with that in 

 the upper part of the canal. In the 

 tirst case, a boat may be floated into 

 the lock from the lower part, and 

 then, if the lower gates be closed and 



water is admitted from the upper 

 level, the canal-boat is raised, by the 

 depth of water thus added to the 

 lock, to the upper level, and on the 

 complete opening of the gates it is 

 thus floated onward. By reversing 

 the process, it will readily be under- 

 stood how the boat may, in like 

 manner, be lowered from the higher 

 to the lower level. The greater the 

 lift or the lowering, the more water is 

 consumed in the process of exchange 

 from one level to another; and where 

 the traffic of the canal is great, a 

 large supply of water is required to 

 carry it on, which is usually provided 

 by capacious reservoirs situated above 

 the summit level. Various expedients 

 are adopted for economising water : 

 thus, when the width of the canal 

 will admit of it, the lock is made in 

 two compartments, communicating 

 with each other by a valve, which 

 can be opened and shut at pleasure ; 

 and by this means one-half of the 

 water which it Avould otherwise be 

 necessary to discharge to the lower 

 level may be transferred to the other 

 compartment. 



.LAN OF LOCK. 



