CANAL LOCKS. S49 



the top edges of these are hollowed into a curve, as shown improvement 

 in the figures. B A^ is a carriage loaded with two heavy tcnave water 

 leaden weights, and resting on four low brass wheels, 

 having grooves in their circumferences like sash pullies, 

 to receive the iron bars upon the frames b and a, so that 

 the carriage can be drawn along upon them ; the distance 

 of the axles of their wheels is such, that when the wheels 

 at B rest on the frame over two of the posts c, c, the 

 wheels at A shall at the same time rest over the other two 

 posts c, c, as shown in Fig. 1 ; and when the wheels at B 

 rest over two of the standards e, e, the wheels at A shall 

 at the same time rest over the other two standards e, e, in 

 Fig. 2. In order to work the model, the carriage must 

 be brought into the position shown in Fig, 1, and this 

 can readily be done by stops, which are provided in the 

 proper places on the curved bars, for preventing the 

 wheels from rolling too far; as much water must then be 

 poured into the lock C, as will fill it exactly to the black 

 line c?, «/, withinside the same ; and if the table on which 

 the model stands be not level, small wedges or chips 

 must be put under the model where necessary, until the 

 surface of the water exactly corresponds, all round the 

 lock, with the top water-mark or line above-mentioned ; 

 it must likewise be observed, to place the model across ^ 

 the table, so that the weight A, wJien hung over the puU 

 ley/ or g*, may be at liberty to descend. Then hang 

 the two-pound weight h^ Fig. 1, by the line over the pul- 

 ley/, at the upper end of the lock ; and the carriage, or 

 load B, A, will, be drawn forward into the position shown 

 at Fig. 2, and the water in the lock C will pass through 

 the shuttle, to buoy up tlie caisson D, and its surface in 

 the lock will descend to the lower level. Again, by 

 shifting the weight to the lower end g^ the load will 

 again be brought back, the caisson depressed, and th« 

 water forced through the shuttle, again, raised to th« 

 higher level d, d, in the lock, as in Fig. 1. 



Hence it is evidenf that the water in the lock, with or 

 without a boat therein, may be raised or lowered, by th9 

 application of any force to move the carriage or load, 

 horizontally on wheels. That when it is intended to pass 

 a boat from the upper to the lower canal, the water in 



Vol. XV.— SwpLEMENT. Bib th» 



