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LVI. A proposed Hydraulic Experiment. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



IN the issue of this Journal for October 1918 (p. 315) 

 Lord Payleigh has proposed an experiment on the flow 

 of a liquid between two cylinders, standing side by side, and on 

 the influence of a rotation of these cylinders on the form of the 

 stream-lines. May I draw your attention to a remark by 

 Prof. F. Prandtl of Grottingen, put forward in a discussion at 

 a meeting of November 1911 and published in the Zeitschrift 

 fur Flugtechnik und Motorluftschiffahrt, iii. p. 32 (1912), on 

 an experiment which is only slightly different from that 

 proposed by Lord Rayleigh? It is stated there that no 

 vortices (eddies) arise if care has been taken that everywhere 

 the parts of the walls go faster than the adjacent fluid. If 

 two cylinders, standing side by side, very near to each other, 



rotate in opposite directions, it is possible to make the stream- 

 lines close perfectly behind the cylinders. The arrangement 

 differs from that as proposed by Lord Rayleigh only as 

 far as the flow is directed along the exterior sides of the 

 cylinders, and not between them. Photographs seem to have 

 been taken of the form of the stream-lines ; however, they 

 have not been published. 



Yours truly, 



Delft (Holland), 



4 Dec. 1918. 



J. M. Burgers. 



