E SES A

twenty-five or thirty tons burthen, at each end thereof is a door-way, which the boat,&c. is to be floated through into or out of the caiſſon, and being received therein, and the

door then ſhut, with a given quantity of wäter to float the boat, and counterpoiſe the caiſlon, ſo as to make it the ſame ſpecifick gravity with the water in which it is immerſed; if may then be eafily raiſed or lowered at pleaſure, either by deſtroying the equilibrium, by admitting a ſmall quantity of water into the caiſſon through a valve conſtru&ed for that purpoſe, or by diſcharging a ſimilar quantity through ano-

ther valve, or by chains and rollers, as in the drawing an- nexed, from one level to another, and the boat be floated from the caiſſon into the canal; the water in the caiſſon and that in the canal having both the ſame level whilſt the con- veyance is effected.

B. is one ſide the bottom, and one end of the lock or ciſtern in which the caiſſon is immerſed, which is built of

free-ſtone, and of the following dimenſions, viz. from the foundation to the top of the wall ſixty-ſix feet, length from out to out eighty-ecight feet, width in the middle twenty feet, ditto at each end eleven feet and half, and the perpen- dicular height from the ſurface of the lower canal to that of the upper canal forty-ſix feet.

C. The door at each end of the caiſſon, which ſhuts into a rabbet, the frame proje&ing about three inches beyond the door when ſhut.

D. An aperture at each end of the ciſtern or lock, com- municating with the upper and lower canal, with a fliding door or gate, which are counterpoiſed like a common ſaſh, and wound up by wheel and pinion, to receive the end of the caiſlon, to which it is cloſely fitted at the time the boat 1s received or delivered,|

R. VW ELDON,