LIFT FOR CANALS. 339 



lower level, the narrow space between the paddle of the trough Machinery for 



and that of the canal, is first filled with water, by opening a raisi "R lind 



* - 9 . lowering boats 



valve, the situation of which is pointed out by the letter H, in upon canals 



fig. 2 and 4, Plate IX. ; the lateral pressure of the water against wltnowt the 



° * ,1,7 same ex pence 



the paddles, is thus removed : The small chain, which hangs f water as by 



down between the upright posts, the lower part of which is 'ocks. 

 double, is then linked to the hooks of both paddles, and by 

 means of the crane near the end, they are drawn up together, 

 and the boat floats into the trough j the paddles arc then drop- 

 ped, and the trough raised to the upper level, when the boat is 

 liberated by opening the paddles at the contrary end. A similar 

 operation takes place, when a boat is required to descend from 

 the upper to the lower level. 



Plate IX. Figure 1, a section of the end of the machine ; this 

 clearly shews the principle by which the weight is raised, viz. 

 that of the simple pulley, where the weight suspended on each 

 side being equal, a force sufficient to overcome the unavoidable 

 friction being applied, puts the whole in motion either way. 

 A /4 represents the section of the trough, suspended from the 

 iron beam C D C, by rods, the lower ends of which are fasten- 

 ed by screws and nuts at B B, and the upper ends are fixed in 

 the same manner at C €. 



From the centre D of the beam CDC, proceeds a very 

 strong double chain D D d E, passing over the wheel H H. 

 From the end E hangs an iron rod E FG, which passes through 

 a thick square platform of oak at G, loaded with brick- work ta 

 the weight of eight tons j this is the case with each of the 

 others j the weight, therefore, of the whole, is 64 tons, being x 

 equal to that of the trough, which they hold in equipoise. 



// H 3 a cast-iron wheel, 12 feet in diameter, one of the eight 

 which are seen in Plate I. IK, the centre wall, 30 feet high. 



From L, under the centre of the trough, is suspended a chain, 

 which is loaded at equ.il distances with blocks of iron, 1, 2, 3, 

 4, 5 ; the weight of them is equal to as much of the chain and 

 rod DdEFG, as hang in a perpendicular direction. The 

 weights F G, are provided with similar chains, so that, as in the 

 present instance, when they are at the lower level, the opposite 

 blocks are called into action, and counterbalance the force of 

 that portion of chain and rod, extending from d to G, while the 



blocks 



