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electrons. In this case the equations serve to determine the accelerations, 
the velocities are to be considered in this case as independent variables. 
2. For some electrons m and M are zero. In this case the accele- 
rations disappear from the equations. Now we can solve the com- 
ponents of », and w in determinant form, as they form a set of six 
linear equations. The elements of this determinant are integrals which 
are to be extended over the electron, and are known if € and ® 
have been given in every point. So », and w appear not to be 
independent variables in this case. The number of variables is, 
therefore, smaller than in the case that the masses are not zero. 
And this is not strange: in the expression of the kinetic energy the 
velocities of the electron do not occur when we ascribe the energy 
to the medium. Only if by the supposition of a quasi-stationary 
motion a connection is established between the motion of the electron 
and the forces of the field, the equation of the energy can be reduced 
to such a form that », and w oceur in it. 
The values of v, and w thus found must now be substituted in 
d dE 
the equation c Rot ) = 5 + ov to find the value of Sa 
dt z 
If we now examine in how far supposition A has been fulfilled, 
it is at once evident that this is certainly the fact in the first case. 
itn cee | 
Then — =O even for every variable separately. 
Op 
. . ET Över . 
In the second case, however, it is different, then ox 38 not zero. 
For the integrations occurring in the elements of the determinant 
which determines v,, must be extended over another region when 
the electron is displaced. When differentiating we should bear in 
mind that ©. is determined from o, whereas g changes in the points 
of the space if the electron is displaced, so that Eis to be considered 
as: function. of X,Y oz 
R dS) cf AS é ‘ ms 
Ie follows from SS hots that EE is independent of .9,so 
dt dt 
d5 dx 
dt dt 
that the terms ——— are zero. The same holds for the terms —— 
0. dE, 
for elements which fall outside the electrons; but not for terms inside 
: dE. dE : 
them. For there is determined by cat = Rot, ) — EV: and vx 
at at 
: dE, 
being dependent on &,, this is also the case for Sie It is true that 
t 
