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and this I have done by showing that the jet would pro- 
duce no effect on the ball unless actually touching it. 
Secondly, I wished to show that the horizontal equilibrium 
of the ball was due to its rotation; and thirdly, to find the 
limiting positions of that point on the ball in which it might 
be struck and remain in equilibrium, and moreover the 
nature of the equilibrium. 
The apparatus employed in these experiments consisted 
of a wheel three inches in diameter and half an inch broad 
at the rim, made of painted wood, capable 
of turning very freely about its axis, and 
suspended by two wires with its axis 
horizontal, so that it could swing like a 
pendulum. A vertical jet of water was 
so arranged that it could be made to 
strike the reel at any point from below, 
or to miss it altogether. This was done 
by bringing the jet out of a horizontal 
pipe which would slide backwards and 
forwards in the same direction as the wheel could swing. 
This pipe was furnished with a cock, so that the force of 
the jet might be altered. 
In experiment No. 1, the pipe from which the jet issues 
was pushed so forward that the jet missed the reel by about 
an inch, and the jet was turned on to rise about six feet 
above the reel ; the pipe was then brought back until the 
water passed as near as possible to the reel without touching 
it — but there was no apparent effect produced on the reel. 
The tap was turned so as to increase and then diminish the 
height to which the jet rose — still, without any effect. 
Experiment No. 2 was made with the same apparatus as 
No. 1. The reel was then changed for one six inches in 
diameter and the same experiment repeated. 
The jet was placed so that it missed the reel (when hang- 
ing freely) by about two inches, and the water was turned 
