ON StPHONS AND JETS OF WATER, 



fluid in the longer leg, which is not counterbalanced by the fluid in 

 the shorter; that is, to the height of the surface of the upper 

 vessel above that of the lower one, or above the end of the siphon, 

 when it is no longer immersed; for the height of the pipe is in all 

 cases to be considered as constituting a part of that height which 

 produces the pressure. Thus the discharge of a pipe, descending 

 from the side or bottom of a vessel, is nearly the same as from a 

 similar horizontal pipe, inserted into a reservoir of the whole height 

 of the descending pipe and of the fluid above it ; and this is true 

 even when the depth of the vessel is inconsiderable, in comparison 

 with the length of the pipe, if its capacity is sufficient to keep the 

 pipe running full. It appears at first sight extremely paradoxical, 

 that the whole water discharged, each particle of which is subjected 

 to the action of gravitation in a pipe 16* feet long, for hair a second 

 only, should acquire the velocity of 32 feet in a second, which 

 would require, in common circumstances, the action of the same 

 force of gravitation for a whole second, and this fact may be con- 

 sidered as favourable to the opinion of those, who wish to estimate 

 the magnitude of a force, rather by the space through which it is 

 continued, than by the time during which it acts; but if we attend 

 to the nature of hydrostatical pressure, we shall find that the effect 

 of the column on the atmosphere is such, as to produce, or to 

 tlevelope, a portion of accelerating force which is actually greater 

 than the weight of the particles immediately concerned. If a doubt 

 could be entertained of the truth of this theory, it might easily be 

 removed by recurving to the general la\v of ascending force, since 

 it follows from that law, that each panicle, which descends in any 

 manner through the space of l6 feet, must acquire, either for itself 

 or some other particles, a power of ascending to the same height ; 

 and on the other hand, the event of the experiment confirms the 

 general law. For if we fix a shallow funnel on a vertical pipe, and 

 pour water into it, so as to keep it constantly full, while the pipe 

 discharges itself into a reservoir, out of which the water runs 

 through a second pipe, placed horizontally, of exactly the same 

 dimensions with the first, the height, at which the water in the 

 reservoir becomes stationary, will be very nearly equal to the height 

 of the funnel above its surface, so that the same height produces 

 the same velocity in both cases. 



We may understand the action of the forces immediately con. 



