Manchester Memoirs, Vol. Iv. (191 1), No. 13. 5 



Another fact which the experiments appear to indicate, 

 is that the tendency to eddy formation in the relative 

 motion of a fluid and a soh'd surface is greater, for a given 

 relative motion, when the fluid as a whole is moving past 

 a stationary surface, than Vv'hen the surface is moving 

 through still fluid. This receives indirect confirmation 

 from experiments by Stanton, Beaufoy, Froude, Dubuat, 

 and Morin, on the resistance of plane surfaces when 

 moving through still water, or when held stationary in a 

 moving stream. The results indicate that for a given 

 relative velocity of plane and water, the resistance is 

 greater in the latter case. A possible explanation of this 

 would appear to lie in the fact that in the former case, i.e., 

 with a moving plate in still water, the fluid, except in the 

 immediate vicinity of the moving surface, is in a stable 

 condition, and any eddy projected from the neighbourhood 

 of the surface will be dampfed with a minimum disturbance 

 of the surrounding fluid. On the other hand, with a body 

 of fluid in motion, even if the motion remote from the 

 centre of disturbance is stable, the balance of stability is 

 less than in the former case, and any slight disturbance 

 will have more widely reaching effects, and will lead to an 

 increased loss of energy. 



