180 HYDRAULICS. 



And, to observe how small an inclination will 

 answer this purpose, one need only take a couple 

 of jars full of water, and hang a small syphon, 

 whose legs are of equal lengths, upon the edge of 

 one ; the external leg whereof will, from the slop- 

 ing of the jar, naturally incline a little, and the 

 syphon will soon begin to act ; then taking it on 

 the edge of the other jar, the like will immediately 

 happen ; and thus reciprocally the effect may be 

 produced as often and as suddenly as you please. 



It is evident from what has been said, that when 

 the two legs of the syphon are of equal length, 

 they are equally pressed by the atmosphere, and 

 consequently no motion ensues ; but when the 

 syphon is inclined, the perpendicular height of the 

 one is made greater than that of the other, and the 

 weight of the water in the one overbalances that 

 in the other, and begins to flow. On this account, 

 in practice, one of the legs of the syphon is made 

 longer than the other, that the effect may take 

 place without inclining the instrument. 



In order to make a syphon act, it is necessary, 

 first, to fill both legs quite full of the fluid, and 

 then the shorter leg must be placed in the vessel 

 to be emptied. Immediately upon withdrawing 

 the finger from the longer leg, the liquor will flow. 

 If the perpendicular height of a syphon, from the 

 surface of the water to its bended top, be more 

 than S3 feet, it will draw no water, even though 

 the other leg were much longer, and the syphon 

 quite empied of air ; because the weight of a 

 column of water 33 feet high, is equal to the 

 weight of a column of air reaching from the sur- 

 face of the earth to the top of the atmosphere. 

 Mercury may be drawn through a syphon, in the 



