HYDRAULICS. 181 



same manner as water ; but then the utmost height 

 of the syphon must always be less than 30 inches, as 

 mercury is nearly 14 times heavier than water. The 

 syphon may be rilled, by pouring some of the fluid 

 into it, or by placing the shorter leg in the vessel, 

 and sucking the liquor through the longer leg. 

 Some, as Fig. 15., are made witli a sucking-pipe 

 attached to the longer leg. Syphons are extremely 

 convenient for decanting liquors of various kinds, 

 as they do not disturb the sediment. 



A syphon may be disguised in a cup, from which 

 no liquor will flow until the fluid be raised therein 

 to a certain height ; but when the efflux is once 

 begun, it will continue until the vessel be emptied. 

 For instance, fig. 16. Plate 8. is a cup, in the 

 centre of which is fixed a glass pipe, continued 

 through the bottom, over which is put another 

 glass tube, made air-tight at top by means of the 

 cork, but left so open at foot, by holes, that water 

 may freely rise between the tubes as the cup is 

 filled : until the fluid in the cup shall have gained 

 the top of the inmost pipe, no motion will take 

 place ; the air, however, from between the two 

 pipes, being in the mean time extruded, by the 

 rise of the denser fluid, and passing down the 

 inner tube, will get away at bottom ; and the 

 water, as soon as the top of the enclosed tube shall 

 be covered thereby, will very soon follow, and 

 continue to rise in this machine, as in the syphon, 

 until the whole has run off. This is called Tan- 

 talus' cup ; and to make the thought more humor- 

 ous, a hollow figure is sometimes put over the 

 inner tube, of such length, that when the fluid has 

 got nearly up to the lips of the man, the syphon 

 may begin to act, and empty the cup. It is, in 

 effect, no other than if the two legs of the syphon 



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