Ifi'DRAULICS. i;<) 



of tlic water in the reservoir ; but it will not rise 

 quite so high, owing to the resistance of the air and 

 the friction in the ajutage. 



THE SYPHON. 



A syphon, generally used for decanting liquors, 

 is a bended pipe, whose legs are of unequal lengths, 

 as A B (Plate 8. fig. 14.) If a small bent tube, 

 whose legs are of equal lengths, be filled with 

 water, and turned downwards, the fluid will not 

 run off) but remain suspended therein, so long as 

 it is held exactly level ; but when an inclination is 

 given to either leg, whereby the perpendicular alti- 

 tude of one is in effect made shorter than the other, 

 the water will flow from the lowest leg, and will 

 continue to run till the vessel is emptied. 



The theory of this is as follows : the air is a 

 fluid, whose density near the surface of the earth 

 is experimentally found to be to that of water, at 

 a medium, as to 1 to 850 ; so. that 850 gallons of 

 air, near the earth, weigh as much as one gallon 

 of water. Now, according to the nature of all 

 other fluid bodies, the air presses the surface of all 

 things exposed to it every way equally. When, 

 therefore, the legs of the syphon, equal in length, 

 are turned down, the weight of the atmosphere 

 above being kept off by the machine, the under 

 air, bearing against and repressing the water which 

 tends to fall out of both of them with equal force, 

 keeps it in suspense, and prevents its motion ; but 

 when, by inclining it to either side, we in effect 

 shorten one of its legs, and lengthen the other in 

 perpendicular altitude, the balance is destroyed, 

 and the longest will preponderate. 



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