184 WELLS'S NATURAL PHILOSOPHY. 



ing the water up, equal to ono atmosphere: consequcntlj^, a column of water 

 will be sustained, or projected to a height of 34 feet. When the air is con- 

 densed into ono third of its bulk, its elastic force will be increased three- 

 fold, and it will then not only counterbalance the ordinary atmospheric 

 pressure, but will force the Avater upward with a pressure equal to two at- 

 mospheres, or 64 feet, and so on. The ordinary fire-engine is simply a conve- 

 nient arrangement of two forcing-pumps, furnished with a strong air-chamber, 

 and which are worked successively by the elevation and depression of two 

 long levers called brakes. 



What is a 395. The Syphon is an apparatus by which 

 Syphon? g^ liquid can be transferred from one vessel to 

 another without inverting, or otherwise disturbing the 

 l^osition of the vessel from which the liquid is to be re- 

 moved. 



In its simplest form, the syphon consists of a bent 

 tube, A B C, Fig. 179, having one of its branches 

 longer than the other. If we immerse the short arm 

 in a vessel of water, and by applying the mouth to 

 the long arm, as at C, exhaust the air in the tube, 

 the water will bo pressed over by atmospheric pres- 

 sure, and continue to flow so long as the end of the 

 lower arm is below the level of the water in the vessel 

 „ The action of the syphon is readily 



principle does explained: the column of liquid in 

 the syphon act? ^j,^ ^^^^^^ ^^^^ ^^^ ^,,3^ reaching in 



the shorter arm from the top of the curve or bend to the surflice of the liquid 

 in the vessel, have both a tendency to obey the attraction of gravity and fall 

 out of the tube. This tendency is opposed, however, on both sides, by 

 atmospheric pressure, acting on one side at the opening C, and upon tho 

 other upon the surface of the liquid in the vessel, thus preventing, in tlie 

 interior of the tube, tho formation of a vacuum, wliich would take place at 

 tho curve, if the two columns ran down on both sides. But tho column 

 on one side being longer than upon the other, the weight of the long 

 column overbalances the short one, and determines the direction of tho 

 flow; and in proportion as the liquid escapes from the long arm, a fresh 

 portion is forced into the short arm on the other side by the pressure of 

 tho air. The syphon is, therefore, kept full by the pressure of the atmos- 

 phere, and kept running by the irregularity of the lengths of tho columns in 

 its branches. 



A SMction-tubo is sometimes attached to the syphon to make it more use- 

 ful and efficient, as is represented in Fig. 180. By this means we may fill 

 the whole syphon without the liquid entering the mouth, by sucking at 

 the end of the suction-tube, and temporarily closing the end of the longer 

 arm. 



In order that tho discharge of a liquid by means of the syphon should bo 



