280 PROF. O. REYNOLDS ON THE SUSPENSION 



respect to these assumptions, the fact that the ball will 

 come back again into the jet when driven entirely away 

 from it must upset the truth of the first,, and at the same 

 time it appears to establish the truth of the second. How- 

 ever, some experiments, which will be subsequently de- 

 scribed, made with a view to ascertain if this current exists, 

 show that it does not. Besides w^hich, Mr. Routledge and 

 Mr. Wild have made some experiments. The former found 

 that when the jet, directed horizontally to avoid the influ- 

 ence of the falling drops, was brought very near to a light 

 ball suspended by a thread, the ball showed no tendency 

 to move towards the jet ; and Mr. Wild settled the point 

 by showing that the action of the ball is the same in a 

 vacuum as it is in air. It appears, then, that neither of 

 these assumptions is satisfactory. 



Now, of the forces which act on the ball, its weight acts 

 at its centre in a vertical line, and is the only force which 

 is not due to the action of the water. When the jet strikes 

 the ball directly underneath, it will produce a force acting 

 upwards in a vertical line, the magnitude of which depends 

 on the height, and may therefore balance the weight of the 

 ball. In this position the ball is, by the action of these 

 two forces, in equilibrium, in the same manner as if it were 

 balanced on a point. The slightest deviation in the jet will 

 upset it ; and then the jet will strike it on one side of the 

 vertical line through its centre : when so struck, the forces 

 at the point of contact may be resolved into two, of which 

 one acts along the normal to the surface, or tln'ough the 

 centre of the ball, and is due to the impulsive action of the 

 water (this is called P) , and another in the tangent plane at 

 the point of contact {p) (this is due to the friction of the 

 water, and is called R). If W be the weight of the ball, 

 then P, R, and W are the only forces which at first sight 

 appear to exist ; and the question is, can the ball be in 

 equilibrium under the action of P, R, and W ? This question 



