SUSPENSION OF A BALL BY A JET OF WATER. 279 



XXII] . On the Suspension of a Ball by a Jet of Water. 

 By Osborne Reynolds, M.A., Professor of Engineer- 

 ing, Owens College, and Fellow of Queens' College, 

 Cambridge. 



Eead March 8th, 1870. 



When a ball made of cork, or any very light material, is 

 placed in a concave basin, from the middle of which a jet 

 of water rises to the height of four or five feet, the jet 

 maintains the ball in suspension ; that is to say, it takes 

 and keeps it out of the basin. The ball is not kept in one 

 position, it oscillates up and down the jet; nor is its centre 

 kept exactly in a line with the jet, it often remains for a 

 long time on one side of it. In fact, the ball appears to 

 be in equilibrium when it is struck by the jet in a point 

 about 45° below the horizontal circle. In this way, for 

 some seconds at a time, the ball appears as though it were 

 hanging to the jet, and then oscillates in an irregular 

 manner about this position. If its oscillations become so 

 great that it leaves the jet, it instantly drops, but in de- 

 scending it generally comes back into the jet before it 

 reaches the basin. The friction of the water causes the 

 ball to spin rapidly ; and as it moves about the jet, it spins 

 sometimes in one direction, sometimes in another, always 

 about a horizontal axis. Of the water which strikes the 

 ball, part is immediately splashed off in all directions, part 

 is deflected off at the tangent, and part adheres to the ball, 

 and is carried round with it, until it is thrown off by cen- 

 trifugal force. 



The only explanations of this that appear to have been 

 offered are based on one or the other of the following assump- 

 tions, viz. that the centre of gravity of the ball remains 

 directly over the jet, or that the jet is accompanied by a 

 current of air which tends to carry the ball into it. With 



