276 



PRESS. 



148. The Fire Engine. This is only a modification 

 of the forcing pump with an air 



vessel, as just described. 



Two cylinders M and M' are 

 connected with the air vessel V 

 by means of the valves D and 

 D', and the pistons are worked 

 by means of a lever GEG', the 

 ends of which are raised and de- 

 pressed alternately, so that one 

 piston is ascending while the 

 other is descending. Water is thus continually being 

 forced out of the air vessel through the vertical pipe EH, 

 which has a flexible tube of leather attached to it, by means 

 of which the stream can be thrown in any direction. 



149. Bramah's Press.* This press is a practical ap- 

 plication of the principle of the equal transmission of fluid 

 pressures (Art. 8). In the vertical 



section of this instrument (Fig. 

 78), A and C are two solid pistons 

 or cylinders fitting in air-tight col- 

 lars, and working in the strong 

 hollow cylinders L and K, which 

 are connected by a pipe BD. At 

 D is a valve opening upwards, and 

 at B is a valve opening inwards, a 

 pipe from D communicating with 

 a reservoir of water. M is a mova- 

 ble platform, supporting the substance to be pressed, and N 

 is the top of a strong frame. HOF is the lever working 

 the cylinder C, F being the fulcrum, and H the handle. 

 Action of the Press. Let C be raised ; the atmospheric 



* The principle of this press was suggested by Stevinus. It remained unfruitful 

 in practice until 1796, when Bratnnh, an English engineer, by an ingenious con- 

 trivance, overcame the only difficulty which prevented its practical application. 



Fig. 78 



