1892.] in a system of moving molecules. 327 



ultimately absolutely steady is after all not greater than the 

 assumption that it is ultimately perfectly regular, and if the 

 regularity of the distribution both in space and time is assumed 

 Maxwell's law of distribution appears, from the above, readily to 

 follow. 



Monday, May 2, 1892. 

 Prof. G. H. Darwin, President, in the Chair. 



The following were elected Fellows of the Society : 



Thomas Clifford Allbutt, M.D., F.R.S., Fellow of Cams College, 



Regius Professor of Physic. 

 David Sharp, M.A. (M.B. Edin.), F.R.S., Curator in Zoology. 

 J. C. Willis, B.A., Gonville and Caius College. 



The following was elected an Associate : 



A. Antunis Kanthack (M.B. Lond.), St John's College, John 

 Lucas Walker Student in Pathology. 



The following communications were made to the Society : 



(1) The application of the Spherometer to Surfaces which are 

 not Spherical. By J. Larmor, M.A., St John's College. 



The ordinary form of spherometer, which is used for measuring 

 the curvatures of lenses, rests on the surface to be measured by 

 three legs which are at the corners of an equilateral triangle ; and 

 the mode of using it consists in finding the length of the ordinate 

 drawn up to the surface from the centre of the triangle formed by 

 the points of support, by means of a micrometer screw moving 

 along the axis of the instrument. 



In the actual use of the instrument the surface to be measured 

 is assumed to be spherical ; and the question has apparently not 

 occurred to examine the character of the results which may be 

 derived from its application to a surface of double curvature. 



On actual trial with such a surface, for example the cylindrical 

 surface of an iron pipe, it appears at once that when the centre is 

 set at a given point the instrument may be rotated anyhow on its 

 axis without affecting its reading. It therefore measures some 

 definite quality of the double curvature of the surface at the 

 point. There is a temptation to hastily assume that the plane of 

 support is parallel to the tangent plane at the centre of the instru- 



