294 
MOVING FORCE. 
Cases of diffi- solution of this question; and many valuable experiments 
docnines'of have since been made on effluent water ; yet I cannot find that 
moving force. results of any direct experiments have been published which 
go to determine the precise amount of this reaction. 
Sir Isaac Newton suggested (Principia, first edit. p. 332) a 
method by which the reaction may be easily measured. If the 
vessel be suspended like a pendulum, he observes, it will recede 
from the perpendicular in the opposite direction to the jet.— I 
have made some experiments on a vessel suspended in that 
manner, and in order to ascertain the reaction as accurately as 
possible, I made use of a balance beam furnished with a per- 
pendicular arm of the same length as the horizontal arms, as 
represented at fig. IS. The scales were exactly balanced, and 
the end of the rod D made just to touch the side of the vessel, 
—The orifice was then opened, and the water in the vessel was 
kept uniformly at the same height by a steam falling gently on 
the plate E. The scale F having been raised by the reaction of 
the jet, weights were put into it till itUvas brought exactly to 
the position in which it was before the orifice was opened. The 
diameter of the vessel was 7 inches, and the height B C exactly 
3 feet. I tried orifices of various diameters from ,35 to .7 of 
an inch. Their exact diameters were ascertained by a micro- 
meter, and the time carefully observed in which 30lbs. of water 
were discharged through each orifice. 
When the orifice was made in a thin plate (srV of an inch in 
thickness,) I found the re-action to be greater than Sir Isaac 
Newton’s first conclusion, in the ratio of 1-14 to 1. There 
was some variation in the results of the experiments. The 
greatest reaction, how'ever, was as l'l6 to 1, and the least as 
1‘09 to 1, which fall far short of Sir Isaac Newton’s last 
inference. The velocity of the water at the orifice (ascertained 
by observing the time in which 30lbs. were discharged) was 
less than that which a body would acquire in falling freely from 
B to C, in the ratio of '6 to 1 . 
I found no constant ratio to subsist between the diameter of 
the contracted vein and that of the orifice j and observing con- 
siderable opacity in the jot at the contracted vein, I concluded 
it 
