236 



Mr. -I H. .loans. 



Li'jni'1 Flow. 



('() Pressure gratlient. 



(/<) Kate of flow per unit width of 



liquid layer. 

 (') Ratio of (b) to (a). 



fir Iii'/'irtion. 



(a) Magnetic intensity or f < . 

 (/?) Magnetic induction, 

 (y) Permeability = ratio of (y8) 

 to (a). 



From this it is evident that the permeability corresponding to a 

 given ratio of thicknesses of the liquid layer is given by the ratio of 

 the rates of flow, per unit width of layer, for the two thicknesses, 

 iissuming the same pressure gradient for both. The connection 

 l>etween the rate of flow and the thickness for a given gradient of 

 pressure was carefully investigated in a series of preliminary experi- 

 ments, and it was found that the rate of flow varied as the ail*- of the 

 thickness a result which was afterwards confirmed by a theoretical 

 investigation. The permeability in the magnetic problem is thus given 

 by the ratio of the culms of the two thicknesses. 



A stream-line diagram corresponding to the theoretical diagram 

 given above was next obtained, and on superposing the two it was 

 found that their lines were practically coincident. 



The soundness of the method as applied to two-dimensional problems 

 in magnetic induction having been thus established, the authors pro- 

 ceeded to apply it to a number of special cases, many of which could 

 not be successfully attacked by any other method. The paper is 

 accompanied by a large number of photographs, showing the results 

 obtained. Some of these are of importance from an electrical-engi- 

 neering standpoint. 



The method described is the only one hitherto known which enables 

 us to determine the lines of induction in the substance of a solid 

 magnetic body. It is equally applicable to two-dimensional problems 

 in magnetic induction, electrical flow, and heat conduction. 



" The Distribution of Molecular Energy." By J. H. JEANS, K.A.. 

 Scholar of Trinity College, and Isaac Xewton Student in the 

 1'niversity of Cambridge. Communicated by Professor J. J. 

 THOMSON, F.R.S. Pteceived June 14, Read June 21, 1900. 



(Abstract.) 



This paper attempts to examine the well-known difficulties in con- 

 nection with the partition of energy in the molecules of a gas. A 

 definite dynamical system is first considered, an ideal gas in which the 

 molecules are loaded spheres, that is, spheres of radius , of which the 

 centre of mass is at a small distance, r, from the geometrical centre. It 



