PNEUMATICS. 257 



if the air in the tube be sucked out, or otherwise 

 extracted, the water will flow through the tube in 

 a continued stream, providing the height from the 

 surface of the water, to the top of the bending, 

 does not exceed 32! or 33 feet. 



A bent tube of this kind is called a syplion. If the 

 syphon, instead of having the air extracted by suc- 

 tion, be filled with water, and the ends stopped till 

 it is inverted, with the shorter leg immersed in wa- 

 ter, the same effect will follow. 



It is the greater weight of the water in the longer leg 

 of the tube, that determines the fluid to descend on 

 that side, and the pressure of the air continues the 

 supply. 



The syphon may be employed to raise water over a 

 height less than 33 feet, if it is to descend below 

 the level of the fountain on the opposite side. It 

 could not, however, be conveniently applied, if the 

 height was near to 33 feet; because the velocity 

 with which the water in the shorter leg is made to 

 ascend, depending on the difference between that 

 height and 33 feet, the length of the column which 

 the air is just able to sustain, might not afford a suf- 

 ficient supply for the stream descending in the longer 

 leg. 



The syphon is properly a pneumatico-hydraulic ma- 

 chine, the action of water and of air being both ne- 

 cessary to its effect. It is, however, the simplest 

 of all the instruments employed in raising water. 



VOL. I. R 348. 



