C 351 ] 



L. On the Application of Screw-Blades as Floats for Paddle- 

 wheels. By W. G. Adams, M.A ., F. G.S., Fellow of St. John's 

 College, Cambridge, Professor of Natural Philosophy in King's 

 College, London*. 



SINCE my former paper on this subject was communicated 

 to the Philosophical Magazine, experiments {an account of 

 which appeared in the ' Times ' of the 5th of April) have been 

 made at Portsmouth with Dr. Croft's new wheel, on Her Ma- 

 jesty's private yacht ( Elfin/ with very satisfactory results, show- 

 ing in the very first trial that the new wheel is superior to the 

 wheel with ordinary flat floats, and very nearly comes up to the 

 wheel with feathering floats, even with a much smaller surface 

 exposed to the pressure of the water. 



One of the points especially worthy of notice is the fact that 

 "no vibration whatever was experienced on board" \ so that it is 

 no longer a mere matter of theory, but also true in practice, that 

 with the new wheel the sudden jerking and quivering motion 

 have no existence. In my former paper it is stated that if the 



number of revolutions be such that v is greater than — , then 



the part of the float nearest to the axis will tend to stop rather 

 than to propel the boat. This must certainly be the case where 

 the radius of the paddle-wheel is small, as in the case of the 

 ' Elfin/ and may also be the case in a larger vessel. This diffi- 

 culty may be obviated by cutting away the part of the float near- 

 est to the axis ; and I propose to consider the effect of such a 

 change on the resistance and moment about the axis, in order 

 to determine whether the float is rendered thereby more or less 

 efficient. I also propose to investigate the expressions for the 

 resistance and moment on a screw-blade whose pitch is different 

 from 45°, and to determine the efficiency when the pitch is what 

 is practically considered most advantageous. The equations 

 giving the resistance and moment on one float are these : — 



R = i ftcoVJ J ^ -^-± dp d6 



-i P,vcor 3 \ J J|^ g; dp dd 

 -i Pl v{2coa-vy \y^-—dpdO 



* Communicated by the Author. 



