358 Mr. H. N. Allen on Energy Movements in the 



of the consequences of Maxwell's suggestion with regard to 

 energy-distribution. The changes needed in the theory in 

 order to apply it to gravitation are also indicated. 



2. If two equal charges of positive and negative electricity 

 + M and — M are separated by a distance I, the equation to 

 the curve in which the equipotential surface V intersects the 

 plane of the paper is 



M M . (i) 



vy +(¥-*>' yy+'(i?+*J* ' 



the origin being the point midway between the particles, and 

 the X-axis being the line joining this point to the positive 

 particle. 



3. The number of tubes of force proceeding from a charge 

 M has sometimes been taken as M but more generally as 

 4*7rM. For graphical methods the former plan seems most 

 convenient, and in order to avoid confusion it is proposed that 

 the resulting tubes should be called "tubes of polarization," 

 while the smaller tubes retain the name "tubes of induction."" 

 The polarization, as defined by J. J. Thomson in his ' Recent 

 Researches in Electricity and Magnetism,' is measured by 

 the number of these polarization tubes which pass through a 

 square centimetre perpendicular to their direction. 



Using Maxwell's method of drawing the boundary lines 

 between the tubes of polarization, the equation to the /6 th line 

 in the case mentioned above will be 



= + — — -g (-?) 



where the straight line drawn from the positive to the nega- 

 tive particle is called zero, and that drawn in the opposite 

 direction M. 



4. The point of intersection of the equipotential surface V, 

 the line of force n, and the plane of the paper lies on the 

 curves (1) and (2). If, then, I in these equations be regarded 

 as a variable parameter, they will together represent the 

 curve along which the corner of an energy-cell moves, when 

 the two particles come together. To plot this curve, the 

 equipotential surfaces and lines of force might be drawn for 

 a number of different distances between the particles, and 

 corresponding points of intersection joined. 



The path of the energy-cell can be obtained with less 

 labour from measures made on a single diagram, drawn to 

 represent the lines of force and equipotential surfaces about 

 the two particles, when these are separated by a given dis- 

 tance. This is done by taking advantage of the following 

 properties of these lines : — 



