1891.] Temperature and the Refractive Index of Liquids. 343 



of ice, found the value 60,000. Rensch ( Nature,' vol. 21, p. 504), 

 by experimenting on the sonorous vibrations of rectangular plates of 

 ice, found Young's modulus to be 23,632 kilos, per sq. cm. (this last 

 method seems rather dangerous). In attempting to devise an imagi- 

 nary system of strains sufficiently great to render such a recovery as 

 0"! cm. possible, we are soon brought up by the breaking tension of 

 ice. Direct experiments by Moseley give this as 7 or 8 kilos, per 

 sq. cm., and Kidd and myself found it in one case to be 8'3 kilos, 

 per sq. cm., but the fact that the bar of ice in Exp. (11) bore the 

 weight of 2'5 kilos, before any plastic strains had taken place brings 

 it out greater than 15*5 kilos, per sq. cm., and the bar in Exp. (13) 

 was able to endure an even greater stress. 



A similar discrepancy has been noticed in the case of cast iron 

 (Rankine, ' App. Mechanics,' 297). 



Using the latitude given by the uncertain values of the constants 

 the utmost, I have not been able to devise any system of elastic 

 strains which could possibly make the bar rise O'Ol cm., and there is 

 no reason to suppose that the unknown system of strains actually 

 occurring in the experiments would be exceptionally well adapted 

 to such a purpose. I conclude, then, that we have to deal with a real 

 tendency of the forcibly displaced sliding layers to slide back. The 

 rate of recovery, rapid at first, soon falls off. Thus in Exp. (10) 

 there was a recovery of 0'046 mm. in the first 18 minutes, and only 

 0-021 in the next 58. In Exp. (15) after 0'014 in the first 11 minutes, 

 and the same in the next 31, the motion probably came to a standstill 

 after a few hours, practically, if not absolutely. Thus in Exp. (12) 

 the bar was left with no weight on for 12 hours, and the recovery 

 only 0'072 mm. 



[Mr. McConnel died suddenly at Davos while engaged on the fore- 

 going paper, which has been printed from his rough copy with some 

 few alterations of no great importance. I thought it better to do 

 this than to attempt to edit it; though I know from his last letters 

 to me that the author would have himself, if he had lived, been able 

 to leave it in a more finished state than that in which it now appears. 

 -R. T. GK] 



" On the Effect of Temperature upon the Refractive Index 

 of certain Liquids." By W. CASSIE, M.A. Comnrnnicated 

 by Professor J. J. THOMSON, F.R.S. Received February 19, 

 1891. 



n my paper " On the Effect of Temperature on the Specific 

 Inductive Capacity of a Dielectric" ('Phil. Trans.,' A, 1890), the 



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