ON SIPHONS AND JETS OF WATER. 



ever, are of different specific gravities, and hence the weight and 

 pressure of the atmosphere cannot raise them all to an equal height. 

 Tims quicksilver will ascend in an exhaused tube to the height of 

 about thirty inches on the level of the sea, though as the air is 

 lighter or perhaps less elastic at some times than at others, the 

 height of the column will vary tttween the limits of 27 and 31 

 iiicues : and we hence obtain the useful and well known instrument 

 denominated a barometer, concerning which we s>hall have occasion 

 to speak more at large hereafter. From the greater levity of water, 

 a column of this liquid may be sustained in the tube 'or pipe of a 

 pump to a height of from 30 to 35 feet, the pipe, by means of its 

 valve or sucker, possessing a vacuum on its upper extremity like 

 that of the upper extremity of the barometrical tube. 



It is from this curious fact that we are able, without any addi- 

 tional machinery, to have the water conveyed by pipes supplied 

 from a reservoir or fountain of equal elevation to the upper stories 

 of our houses whose height does not exceed from thirty to thirty- 

 five feet. And hence the origin of natural or artificial jets tfsaux, 

 jets of water or .spouting fountains; the jet being supplied from an 

 elevated head or reservoir by means of artificial tubes or natural 

 channels or conductors. These tubes or conductors, whether 

 natural or artificial, are sometimes bent, and are then called siphon?, 

 and according to the nature and complexity of the curvature, pro. 

 duce a variety of striking and amusing phenomena. 



When a siphon, or bent tube, observes Dr. Young, is filled with 

 a fluid, and its extremities are immersed in fluids of the same kind, 

 contained in different vessels, if both their surfaces are on the same 

 level, the whole remains at rest; but if otherwise, the longer 

 column in the siphon preponderates, and the pressure of the at- 

 mosphere forces up the fluid from the higher vessel, until the equi- 

 librium is restored ; provided, however, that this pressure be suffi- 

 ciently powerful: for if the height of the tube were more than 3i 

 feet lor water, or than thirty inches for mercury, the pressure of 

 the atmosphere would be incapable of forcing up the fluid to it* 

 highest part, and this part remaining empty, the fluid could no 

 longer continue to run. 



If the lower vessel be allowed to empty itself, the siphon will 

 continue ruuuing a* long as it is supplied from the upper, with u 

 velocity neatly corresponding to the height of tliul portion of the 



