Water-pipes and Syphons Jrom disengaged Air, Sfc. 103 



^lass cemented into its side at the height of 32 feet from the 

 open end, be filled with water and inverted in a reservoir, the 

 water will be seen to sink to the height of 32 feet, leaving a va- 

 cuum above, which may be proved in the same way as in the 

 mercurial column. Speedily, however, minute bubbles of air 

 will appear in the water ; and, rising to the surface, will, as in 

 the former case, occupy, in a high state of rarefaction, the va- 

 cant portion of the tube. 



The same phenomenon is exhibited in the action of the sy- 

 phon ; and the description of it in this form brings us nearer to 

 our purpose. Suppose, then, a leaden pipe of 70 feet long bent 

 into the form of a syphon, having the shorter limb, of 34 feet 

 in length, plunged into a deep tank or reservoir to the depth of 

 30 feet, and the end of the longer limb immersed in a small 

 vessel of water (see fig. 2.) attached to, and moveable along with 

 it, in order to prevent the admission of air during the varying 

 action of the syphon. If the air be now exhausted from the 

 syphon by a syringe applied to the end of the longer limb, the 

 atmospherical pressure on the surface of the water in the reser- 

 voir will force it to rise in the syphon, and, descending the lon- 

 ger limb, it will issue in a full stream. If the syphon be then 

 gradually elevated, the water will continue to flow from it, but 

 with less and less velocity ; because, while the atmospherical 

 pressure which forces it to rise in the syphon is constant and 

 uniform, the gravity of the ascending column goes on augment- 

 ing with its increasing length, until, at the height of 32 feet, the 

 two forces come into equilibrium, and the water consequently 

 ceases to flow. The syphun will, however, still continue full, 

 because, both ends being immersed in water, no air can enter to 

 displace the fluid contained in it ; and if the syphon is again 

 lowered, the water, obedient to the renewed atmospherical pres- 

 sure, will again begin to flow. But if, in place of being lowered^ 

 the syphon is raised to the height of 33 or 34 feet, the two 

 columns will separate at the summit, and each will fall in its 

 own limb to the height of 32 feet above the surface of the water 

 in which its lower end is immersed, leaving a perfect vacuum in 

 the upper part of the syphon. If the syphon be immediately 

 depressed to its former position, the columns will again unite 

 and begin to flow; but if retained, in its elevated j^tation, tlie 



