60 THE ATMOSPHERE. 



This instrument is very useful for drawing off liquids 

 without disturbing their sediment. And it may be em- 



floyed for emptying vessels of any size, or even a lake, 

 t would be an invaluable means of removing water 

 from certain lands which could not otherwise be im- 

 proved. A tube formed of bored logs, may be laid from 

 the place to be drained, even over a hill, if it do not 

 exceed thirtytwo feet in height, and down its side so far 

 as to make that the longer limb. Both ends must then 

 be plugged, that the syphon may be filled with water, 

 when the plugs may be removed, and the pressure of 

 the air will force out all the water reached by the end 

 of the log. 



The syphon will continue to act until all the fluid 

 has been consumed, or that discharged shall have at- 

 tained a height equal to that from which it came. 



There is a pretty toy made on this principle, called 

 the cup of Tantalus, from the mythological fable of the 

 being who was condemned to stand in water up to his 

 neck, and yet to die of thirst. The glass exhibits the 

 figure of a human being standing in the centre. When 

 water is poured into it, it rises until it reaches the neck 

 of the image, and immediately begins to pass off through 

 a concealed syphon, and continues till the whole is 

 discharged. 



This instrument also explains the cause of intermitting 

 springs, or those which run for a time and suddenly 

 stop, and then resume their discharge after a certain 

 period. They are produced by the channels through 

 which the water flows, being formed like syphons. 



In some places there are springs which run freely in 

 summer or in dry weather, but discharge no water in 

 the winter, or in wet weather. This is caused by a 

 hollow in the hill being fed by runners, but having, be- 

 side the vent through which the spring flows, a waste- 

 pipe like a syphon, which carries off the fluid another 

 way, as soon as it is sufficiently high. 



Superstitious circumstances are often associated with 

 such springs, but by understanding the principle of the 

 syphon, their marvellous character is easily explained. 



