﻿Lord Rayleigh on JEolian Tones. 435 



so that D . dN/dV is very nearly constant, a result also given 

 by Strouhal on the basis of his measurements. 



" On the whole it would appear that the phenomena are 

 satisfactorily represented by (2) or (3), but a dynamical 

 theory has yet to be given. It would be of interest to extend 

 the experiments to liquids."* 



Before the above paragraphs were written I had com- 

 menced a systematic deduction of the form of / from 

 StrouhaPs observations by plotting ND/V against VD. 

 Lately I have returned to the subject, and I find that nearly 

 all his results are fairly well represented by two terms of (3). 

 In c.G.s. measure 



ND . 1Q ./ 1 3-02\ 



-v =195 ( 1 ~vd) (*) 



Although the agreement is fairly good, there are signs 

 that a change of wire introduces greater discrepancies than 

 a change in V — a circumstance which may possibly be 

 attributed to alterations in the character of the surface. 

 The simple form (2) assumes that the wires are smooth, or 

 else that the roughnesses are in proportion to D, so as to 

 secure geometrical similarity. 



The completion of (5) from the theoretical point of view 

 requires the introduction of v. The temperature for the 

 experiments in which v would enter most was about 20° C, 

 and for this temperature 



Ik 1806 xlO- 7 

 1/= p = -00120 = - 15 Q5 o.G.s. 



The generalized form of (5) is accordingly 



= •195(1-^), (6) 



ND 

 V 



applicable now to any fluid when the appropriate value of v 

 is introduced. For water at 15° C, ^ = '0115, much less 

 than for air. 



Strouhal's observations have recently been discussed by 

 Kriiger and Lauthf, who appear not to be acquainted with 

 my theory. Although they do not introduce viscosity, they 

 recognize that there is probably some cause for the observed 

 deviations from the simplest formula (1), other than the 

 complication arising from the circulation of the air set in 



* < Theory of Sound,' 2nd ed. vol. ii. § 372 (1896). 

 t "Tneorie der Hiebtone." Ann. d. Physik, vol. xliv. p. 80] (1914). 



2 F 2 



