Rotational Oscillation of Cylinder in a Viscous Liquid. 587 



an a particle with a light atom seems to be the most likely 

 agency to promote the disruption of the latter ; for the forces 

 on the nuclei arising from such collisions appear to be greater 

 than can be produced by any other agency at present avail- 

 able. Considering the enormous intensity of the forces 

 brought into play, it is not so much a matter of surprise 

 /that the nitrogen atom should suffer disintegration as that 

 the a particle itself escapes disruption into its constituents. 

 The results as a whole suggest that, if a particles — or similar 

 projectiles — of still greater energy were available for experi- 

 ment, we might expect to break down the nucleus structure 

 of many of the lighter atoms. 



I desire to express my thanks to Mr. William Kay for his 

 invaluable assistance in counting scintillations. 



University of Manchester, 

 April 1919. 



LV. The Rotational Oscillation of a Cylinder in a 

 Viscous Liquid. By D. Costek *, 



THIS problem has been dealt with by Stokes f for the 

 purpose of numerical calculations to determine the 

 viscosity of the air. Still, I think it interesting to publish 

 another solution of the problem which gives more oppor- 

 tunity of discussing the different cases, though it is perhaps 

 less adapted to precise calculations. 



The method to be followed will be in the main the same as 

 that used by Prof. Verschaffelt in the analogous case of the 

 sphere J. We consider the rotational swings about its axis 

 of an infinitely long cylinder which executes a forced vibra- 

 tion. Our object will be to ascertain the motion in the liquid 

 which will establish itself after an infinite time (in practice 

 after a relatively short time §) in order to compute the 

 frictional moment of forces exerted on the cylinder by the 

 liquid. The calculations will be referred to a height of 1 cm. 



The motion of the cylinder may be represented by 

 a. = acospt where a is the angle of rotation. An obvious 

 assumption to be made is that the liquid will be set in motion 

 in coaxial cylindrical shells each of which will execute its 

 oscillations as a wdiole. On this assumption it is not difficult 



* Communicated by Prof. G. ]S T . Watson, M.A., D.Sc. First published 

 in the Amsterdam Proc. May 1918, vol. xxi. p. 193. 

 t Math. Papers, vol. v. p.* 207. 



J Cf. Amst. Proc. vol. xviii. p. 840; Comm. Leiden, 148 C. 

 § Cf. Comm. Leiden, p. 22, footnote. 



2 S 2 



