*338 



LECTURE XXVIII. 



The passage of the pipe being stopped by a valve, which is raised by the 

 stream, as soon as its motion becomes sufficiently rapid, the whole column of 

 fluid must necessarily concentrate its action almost instantaneously on the 

 valve ; and in this manner it loses, as we have before observed, the character- 

 istic property of hydraulic pressure, and acts as if it were a single solid ; so 

 that, supposing the pipe to be perfectly elastic, and inextensible, the impulse 

 must overcome any pressure, however great, that might be opposed to it, 

 and if the valve open into a pipe leading to an air vessel, a certain quantity 

 of the water will be forced in, so as to condense the air, more or less rapidly, 

 to the degree that may be required, for raising a portion of the water 

 contained in it, to any given height. Mr. Whitehurst appears to have 

 been the first that employed this method: it was afterwards improved by 

 Mr. Boulton ; and the same machine has lately attracted much attention in 

 France under the denomination of the hydraulic ram of Mr. Montgolfier. 

 (Plate XXIII. Fig. 323.) 



