771 
is a small positive fraction. It thus appears that the neglected term 
may have an effect, in this case, in changing the apparent value 
of *o, the wave-length corresponding to the free or natural vibra¬ 
tion of the electron. 
§ 6. In Art. 1 of a previous paper 1 ) we have recapitulated the 
formulae applying to the case of the superposition of two opposite 
circular vibrations of unequal amplitudes, travelling with different 
velocities (c r and ty) in the same direction, say in the direction of 
the axis of z. The angle ip which the major axis of the resultant 
ellipse makes with the axis of x is, in previous notation^ 
tl) = ^d = — (v 1 — v 2 ). ( 1 ) 
9 ::- 0 
*) On the elliptic polarization of light transmitted through an absorbing 
gaseous medium, parallel to the lines of an extranéous magnetic field. Bulletin 
lrit. for March 1908, page 129. 
