﻿436 Lord Rayleigh on JEolian Tones. 



motion by the revolving parts of the apparatus. Un- 

 doubtedly this circulation marks a weak place in the method, 

 and it is one not easy to deal with. On this account the 

 numerical quantities in (6) may probably require some correc- 

 tion in order to express the true formula when V denotes the 

 velocity of the wire through otherwise undisturbed fluid. 



We may find confirmation of the view that viscosity enters 

 into the question, much as in (6), from some observations of 

 Strouhal on the effect of temperature. Changes in v will 

 tell most when YD is small, and therefore I take Strouhal's 

 table XX., where D=-0179 cm. In this there appears 



^ = 11°, Y 1 =385, Nx/V^B-70, v u 

 t 2 =Zl% V 2 =381, N 2 /Y 2 =6-48, v 2 . 



Introducing these into (6), we get 



r.-n ate ' 195 (i 20-lvA -195A 20'1v 2 \ 



or with sufficient approximation 

 •52 D 2 V 



We may now T compare this with the known values of v for 

 the temperatures in question. We have 



^ = 1853 x 10" 7 , Pn = -0011Q1, 

 fjL U = n65xlO- 7 , ^ = -001243 



so that 



v 2 = *1596, ^ = -1420, 



and v 2 — v 1 = , 018. 



The difference in the values of v at the two temperatures 

 thus accounts in (6) for the change of frequency both in 

 sign and in order of magnitude. 



As regards dynamical explanation it was evident all along 

 that the origin of vibration was connected with the instability 

 of the vortex sheets which tend to form on the two sides of 

 the obstacle, and that, at any rate when a wire is maintained 

 in transverse vibration, the phenomenon must be unsym- 

 metrical. The alternate formation in water of detached 

 vortices on the two sides is clearly described by H. Benard*. 



* C. R. t. 147, p. 839 (1908). 



