50 



Professor J. J. Thomson 



[March 10, 



positive electricity will tend to draw the corpuscles to the centre ; the 

 mutual repulsion between the corpuscles will tend to drive them away, 

 and they will arrange themselves so that these tendencies neutraUse 

 each other. 



Let us now consider the kind of atom we could build up out of 

 corpuscles and positive electricity. The mathematical investigation of 

 this problem leads to the following results. The simplest atom con- 

 taining 1 corpuscle would have 1 corpuscle at the centre of the 

 sphere of positive electrification ; the 2 corpuscle atom would have 

 the 2 corpuscles separated by a distance equal to the radius of this 

 sphere ; the 3 corpuscle atom would have the 3 corpuscles at the 

 points of an equilateral triangle, whose side is equal to the radius of 

 the sphere ; 4 corpuscles would be at the corners of a regular tetra- 



FlG. 1. 



hedron, whose side is equal to the radius of the sphere ; 5 corpuscles 

 are situated, 4 at the corners and 1 at the centre of a tetrahedron ; 

 6 at the corners of an octahedron ; 7 and 8 are more complicated, 

 as the simplest arrangements for 7 and H, an octahedron with 1 at 

 the centre and a cube, are both unstable ; and for 7 we have a ring 

 of 5 in on(3 plane with 2 on a line through the centre at right angles 

 CO the plane ; and 8 we have the octahedron with 2 inside. These 

 arrangements are shown in Fig. 1. 



When the number of corpuscles is large, the calculation of the 

 positions of equilibrium becomes very laborious, especially the deter- 

 mination of the stability of the various arrangements. I will there- 

 fore treat the subject from an experimental point of view, and apply 

 to this purpose some experiments made with a diiferent object many 



