34 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



tube with a force-pump. The piston p of this pump receives the 

 pressure to be transmitted, and acts like the smaller piston of the 

 theoretical machine; 



Let us now see, by the help of the figure, how these various parts 

 are arranged and worked. 



A B is the force-pump worked by a lever ; the piston p presses the 

 water of the reservoir m into the cylinder M. The pressure exerted 

 by the liquid is transmitted to the piston P, and afterwards to the 

 substances placed upon the plate c. 



FIG 14. Section of a Hydraulic 1 Pump. 



To prevent the escape of water through the cracks of the joints 

 of the piston P and from the cylinders, Bramali conceived the idea of 

 reserving in the walls of the cylinder an annular space, a 1), and of 

 filling this space with a piece of leather cut first into the form of a 

 flat ring and then bent over that is to say, it took the form of an 

 U reversed, as seen in Fig. 14. The water which penetrates below 

 this ring in the annular space exerts its pressure on the lower 

 surfacs of the leather; and the greater the pressure, the more 

 forcibly is the ring applied both against the upper surface of the 



