HYDROSTATICS. 



CHAPTER VII. 

 The Syphon Intermitting Springs. 



IF a bent tube with equal branches, 

 like the letter U, be filled with water, 

 and placing; the thumbs upon its two 

 openings, you turn it upside down, and 

 place it in a basin of water, the liquid 

 will stand in it. Let one of the branches 



fig- 22. 



AB (jig. 22.) be brought out of the 

 water, and over the edge of the vessel: 

 the pressure upon the mouth of the 

 branch at B is equal to the pressure on 

 the mouth at G ; for it is in both cases 

 the weight of the air which presses on 

 the surface of the water I K, and makes 

 the water remain in the tube AG, and 

 which also presses against the water 

 in the tube A B ; and the weight of 

 the air meets with the same weight of 

 water to balance it in both branches, 

 because the height of both is equal. 

 Therefore the water will not run through 

 the tube. But if the branch A B be 

 lengthened to L, then there being 

 a greater weight of water in ABL 

 than in G A, it will overcome the pres- 



sure of the air at L ; the water will 

 flow out of the tube, and the water in 

 the basin will be forced up through 

 A G until the basin is emptied, if the 

 arm AG is held to the bottom, and 

 the bottom is higher than the mouth 

 L of the tube. This kind of tube is 

 called a Syphon, and is very conveni- 

 ently used for decanting liquors from 

 casks or other vessels, when it is wished 

 to draw them off without shaking, or 

 when there is a sediment at the bottom 

 which it is wished to leave. 



The strange appearance of inter- 

 mitting springs, or springs which run 

 for a time, and then stop altogether, and 

 after a time run again, and then stop, 

 is entirely occasioned by the channels 

 in which the water flows being formed 

 like syphons. Thus if A B C (Jig. 23.) 

 represents a hill or mountain, in which 

 there is a hollow E F G, and a channel 

 bent like a syphon F H B leading out 

 of it. The water collected from the 

 rills d, will fill the hollow, and as soon 

 as it rises to the line O P, of the same 

 height with H, it will rise to H in the 

 channel, and then flow out through B, 

 till the whole runs off to the level of F. 

 It will then cease to flow until the hol- 

 low is again filled to the level OP, 

 when it will flow again, and so on. 

 Some springs, called variable or re- 

 ciprocating, do not cease to flow, 

 but only discharge a much smaller 

 quantity of water for a certain time, 

 and then give out a greater quan- 

 tity. This is owing to the hollow 

 being supplied from another hollow, 

 which is situated higher up, and has 

 a common runner going to join the 

 stream below the bend H ; for this 

 runner keeps the stream always sup- 

 plied to a certain degree, and when the 

 lower hollow, which feeds the syphon 

 runner F H, is filled up to H, both 



