for elevating and depressing Water. 327 



forced into the upper canal. And again, when it is floated 

 into the lower canal, as much is again from that canal dis- 

 placed, and forced into the lock. 



On the same principle that water is gained by a descend- 

 ing boai, as above described, it will be observed that no 

 waste ensues in an alternate passage ; and that in an ascend- 

 ing passage a loss of water equal to the boat and its load 

 only takes place. 



It should be understood that as canals are sometimes more 

 or less full of water, locks on this principle must be con- 

 structed to raise and depress, to the greatest extremes that 

 ever happen, from the highest high-water to the lowest low- 

 water mark, and that being so constructed, they will apply 

 to any intermediate heights; the curved plane a being formed 

 to adjust and counterbalance the inclination of the wheels 

 on the other plane I, thereby maintaining an equilibrium, 

 at any intermediate height, which the water in the canal 

 may happen to be at. 



Having described its manner of operating, I shall explain 

 and compare cause and effect; for which purpose it may be 

 requisite first to state, that the load of the carriage B, A, is 

 fifty- six pounds, which weight, when advanced, presses di- 

 rectly over the parts c, c, c, c, with all its gravity bearing on 

 the caisson; but when the load is drawn forwards, it rests 

 entirely on the fixed standards e, e } e, e, and by this change 

 the whole effect is produced. 



Now, if the model be set properly to work, it will be 

 found, that a two-pound weight suspended over the pulley 

 at either end will put the carriage in motion, and thereby 

 raise or depress the water in the lock, and that to do so, 

 the two-pound weight will descend sixteen inches. Hence, 

 two pounds descending sixteen inches may be denoted the 

 cause or power to produce the effect. Further, it follows, 

 that this two-pound weight descending sixteen inches pro- 

 duces the same operation as fifty-six pounds laid in the cais- 

 son would perform, and this sinking of the caisson D may 

 be denoted the direct effect produced by the two-p >und 

 weight. The indirect and requisite effeel being that of de- 

 pressing or elevating the water in the luck C, and the coin- 

 y 4 parison 



