OF CONVEYING BOATS OR BARGES ON CANALS. £39 



2d. Whilft the machinery in other contrivances above al- not liable to 

 luded to, is either wholly or in part liable to injury from water, J^/j ™ 

 the machinery in this (the two fluices as before excepted) is 

 wholly exempt from this difadvantage. 



3d. Whilft caiflbons, coffers, &c. require not only the open* nor requiring 

 ing of one or more fluices, but alio a previous fitting or ad- coe ttln S s » 

 jufting of their ends to the mouth of the canal to prevent the 

 lofs of water, before the boat can enter the lock ; according 

 to this plan, on the opening of a fingle fluice the boat floats 

 at once into the Lock without lofs of water, and Arithout any No lofs of water, 

 fuch delay or difficulty : when I fay without lofs of water, it 

 muft be underftood with this allowance, that if a boat goes 

 down laden, and returns (or another goes up) unladen, the 

 upper level gains a body of water equal to the weight of the 

 cargo, e contra the lower canal gains fimilarly if a boat goes 

 down unladen and returns laden. 



4th. If the water in the upper canal at any time be ever fo If water be 

 abundant, no boat can pafs through the former locks but fy macMnwy need 

 zvorking the machinery ; whereas according to this plan the ma- not be ufed, 

 chinery may be at reft, and the boats pafs on as through the 

 common gate locks, whenever the upper canal can afford the 

 neceflary expence of water. 



Laftly. If at any time the machinery of any one lock of and therefore 

 the former kind (out of the many that may be neceflary in a ^ ™£ B £?^ 

 given length of canal) (hould happen to be difordered, the peded by any 

 whole navigation is at a ft and, whereas in a lock of this con- ine *itable dif- 

 firuction in cafe of fuch an accident, the boats may ftill pafs 

 and repafs as through a common gate lock. 



Let us fuppofe a boat (or barge) to be 20 feet long, and fix Particular fore- 

 feet wide, and to draw three feet water. The folid content " lenC oi * d "nen- 

 will be 360 cubic feet, each of which weighing about 62 * 

 pounds, the burthen will be nearly 10 tons. 



Is it propofed to raife (or fink) this boat eight feet, by means 

 of a plunger of equal area or horizontal fuperflcies with that 

 of the boat. 



The defcent of the plunger muft in this cafe be equal to the 

 afcent of the boat, viz. eight feet, and the height of the 

 plunger muft (as in all cafes) be equal to the fum of both, viz. 

 16 feet; the folid content of the plunger therefore will be 

 1,920 cubic feet, amounting in weight to nearly 53 tons. 



v Let 



