596 Lord Kayleigh on the Relation of the 



The surface-tension calculated from these measurements 

 was (temp. = 30° C.) found to be 77'0 dynes per cm. 



Another plate, not so sharp, gave 7 6 '3 dynes per cm. 



A third, in taking which the wide tube happened to be out 

 of the vertical, gave no definite result on account of the 

 uncertainty of the value of the curvature of the large 

 meniscus. The value of the surface-tension was, however, 

 estimated to lie between 75 and 77 dynes per cm. 



The accepted value for the surface-tension of clean distilled 

 water at 30° C. = 7P3 dynes per cm. (T. P. Hall, Phil. Mag. 

 1893). The method described in this article gives results 

 which are fairly self-consistent. The cause of the difference 

 has as yet not been found and is under investigation. 



The experiments and observations recorded in this note- 

 were made at the Physical Laboratory of the Presidency 

 College, Madras. 



LIX. On the Relation of the Sensitiveness of the Ear to Pitch, 

 investigated by a new Method. By Lord Rayleigh, O.M. y 

 P.R.S* 



IN a former research t I examined the sensitiveness of the 

 ear to sounds of different pitch with results which were 

 thus summarized : — 



c\ frequency =250, .sr= G'O x 10~ 9 , 

 </, „ =384, ^ = 4-0 xlO" 9 , 



c", „ =512, s = A'G xlO--', 



no reliable distinction appearing between the two last 

 numbers. " Even the distinction between G'O and 4*6' should 

 be accepted with reserve ; so that the comparison must not 

 be taken to prove much more than that the condensation 

 necessary for audibility varies but slowly in the singly dashed 

 octave." Here s denotes the condensation (or rarefaction) 

 which in one respect is a maximum and in another a 

 minimum. It is the maximum condensation which occurs 

 during the course of the vibration, but the vibration (and s 

 with it) is the minimum capable of impressing the ear in a 

 progressive wave. The method employed depended upon a 

 knowledge of the rate at which energy was emitted from 

 a resonator under excitation by a freely vibrating tuning- 



* Communicated by the Author. 



t Phil. Mag. xxxviii. p. 365, 1894; Scientific Papers, iv. p. 125. 



