634 Proceedings of the Royal Irish Academy. 
Let C be the cominon centre of gravity of the atoms H and CI, 
and let two circles with radii CH = I and CCl = m be described; 
Fig. 3. 
the atoms revolve in these two circles with the same angular velocity. 
Let 
a = mass of hydrogen atom, 
^ - mass of chlorine atom, 
^' = attraction of hydrogen for chlorine, for unit 
distance and unit mass, 
(J)' = angular velocity of orbital motion. 
Equating the attraction to the centrifugal force of H and CI, we 
find 
m'^m = -r^ ; 
