356 



Mr. J. P. Harrison on the Relation of [Feb. 7j 14, 



February 7, 1867, 



Lieut .-General SABINE, President, in the Chair. 



The following commumcation was read : — ' 



"Account of Experiments on Torsion and Flexure for the Deter- 

 mination of Rigidities.^^ By J. D. Everett, D.C.L., Assistant 

 to the Professor of Mathematics in the University of Glasgow. 

 Communicated by Sir William Thomson. Received January 25, 

 1867. 



(Abstract.) 



These experiments are a continuation of those described in a paper read 

 February 22, 18C6, with some modifications in the apparatus employed 

 which render the comparison between torsion and flexure more direct. 

 The amount of torsion or flexure produced by subjecting a cylindrical rod 

 to a uniform couple throughout its whole length, is measured by means of 

 two mirrors clamped to the rod near its ends, in which, by the aid of two 

 telescopes, the reflexions of a scale overhead are seen and the displace- 

 ments read off. One end of the rod is fixed, and a couple (of torsion and 

 flexure alternately) is applied to the other end. 



Three rods, of glass, brass, and steel, were experimented on, and the re- 

 sults obtained were as follows — M, n, and /c denoting the resistances (in 

 kilogrammes per square millimetre) to linear extension, shearing, and 

 cubical compression respectively, and cr denoting the ratio of lateral con- 

 traction to longitudinal extension : — 





Glass. 



Brass. 



Steel. 



Value of M . , . 



, 5851 



10948 



21793 



„ n 



, 2390 



3729 



8341 





3533 



57007 



18756 





•229 



•469 



•310 



Februart/U.lSer, 

 Lieut.-General SABINE, President, in the Chair. 



The following communications were read ; — 



I. " On the Relation of Insolation to Atmospheric Humidity." By 

 J. Park Harrison, M.A. Communicated by the President, 

 lleceivcd January 30, 1867. 



The occurrence of the maxima of insolation on days of great relative 

 humidity which was noticed by Herr v. Schlagintweit in India*, receives 



Proceedings of the Royal Society, 1865, vol. xiv. p. Ill, 



