﻿Pressure, Volume, and Temperature of Rarefied Gases. 301 



The value of s corresponding to but just audible progressive 

 waves of frequency 256 was found to be 5' 9 x 10 -9 , in 

 sufficiently good agreement with (13) *. 



But if the equilibrium theory be applied to the notes of 

 higher pitch, such as 512, we find the actual sensitiveness of 

 the telephone greater than according to the calculation. In 

 this casef T = l x 10" 8 ; so that by (12) 



,z=5'6xl0- 9 , 

 and 



*=Aa?/S = l\LxlO- 9 , (14) 



decidedly smaller than that (4*5 x 10 -9 ) deduced from the 

 observations upon progressive waves. The conclusion seems 

 to be that for these frequencies the equilibrium theory of the 

 telephone-plate fails, and that in virtue of resonance the sen- 

 sitiveness of the instrument is specially exalted. 



I will not dwell further upon these calculations, which 

 involve too much guesswork to be very satisfactory. They 

 suffice, however, to show that the "push and pull" iheory 

 is capable of giving an adequate account of the action of the 

 telephone, so far at least as my own observations are con- 

 cerned. But it is doubtful, to say the least, whether it could 

 be reconciled with estimates of sensitiveness such as those of 

 Tait and of Preece. 



XXXV. Experiments on the Relations of Pressure, Volume, 

 and, Temperature of Rarefied Gases. By E. C. C. Baly, 

 1851 Exhibition-Scholar in University College, London, and 

 William Ramsay, Ph.D., F.R.S.% 



[Plate XI.] 



THE experiments of which we give an account in the 

 following pages are of two kinds : — first, they relate to 

 the trustworthiness of measurements by means of the McLeod 

 gauge ; and second, they deal with the thermal expansion of 

 gases at low pressures. The behaviour of the ingenious gauge 

 invented by Professor Herbert McLeod has, so far as we know, 

 not been carefully investigated. The thermal expansion of 

 gases at low pressures has been the subject of two investi- 

 gations, one by MendeleefT, and one by Gr. Melander. But 

 many researches have been made on the relations of volume 



* I hope shortly to publish an account of the observations upon which 

 this statement is founded, 

 t Supra, p. 294. 

 \ Communicated by the Physical Society : read June 8, 1894. 



