Moving Force. 235 
demoustrated to be by D. Bernoulli. Sir Isaac 
Newton further observes, that he found, by 
admeasurement, the area of the orifice in a 
thin plate to be to that of the section of the 
contracted vein, at the point of its greatest 
contraction, in the ratio of y 2:1 nearly. 
He takes the re-action, therefore, to be greater 
than what he understood it to‘be when he pub- 
lished the first edition, in the ratio of v2: 1 
nearly. He refers, however, more to experi- 
ment than to theory for a solution of this 
question; ‘and many valuable experiments 
have since been made on effluent water; yet © 
I cannot find that the results of any direct 
experiments have been published which go to 
determine the precise amount of this re-action. 
Sir Isaac Newton suggested (Principia, 
first edit. p. 332) a method by which the 
reaction may be easily measured. If the 
yessel 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 perpendi- 
cular arm’ of the same length as the horizontal 
arms, as represented | at fig. 18. The scales 
were exactly balanced, and the end of the rod 
 @g2 
