484 PROCEEDINGS OP THE AMERICAN ACADEMY. 



side of the simple repulsive particles. Moreover the invariant character 

 of these problems can be brought out both by using the sphere instead of 

 the plane, and by using homogeneous variables and throwing the analyt- 

 ical work into invariant form. I hope, as I have already said, to come 

 back in detail to all these questions. 



Harvard University, 

 Cambridge, Mass. 



