986 
ABRAHAM had calculated # in another way. He started from the 
supposition that equation (3) would not hold, but that we should 
have to correct it into: 
0 
te wang EN 
§ ala ( E) Ber (3a) 
As HE in this equation is the only unknown quantity it may be 
derived from it. This yields again the value of equation (1) for Z. 
In this calculation as well as in that of Poincaré the energy Z has 
been introduced as an amount of potential energy. Moreover ABRAHAM 
assumes that © is the total momentum of the electron, i.e. that the 
electron has only its electromagnetic momentum, which is determined by 
1 
— >< PoyntiNes’ vector and not any momentum of another kind. 
C 
This, however, seems a priori little plausible. For according to the 
principle of the mass of the energy we should expect, that the 
Ww 
electron would possess an amount of momentum / X —, which was 
C 
not of electromagnetic nature. Moreover we should expect, that in 
the moving electron PoincarÉ's pressure would give rise to a transfer 
of energy, which would be accompanied with still another amount 
of momentum. We will therefore denote the total momentum by 
G,., a quality which we will leave undetermined for the present. If 
we do not put a priori ©,,= ©, Apranam’s way of calculating # 
loses its applicability. We must therefore follow a somewhat different 
way for the calculation of £. For this purpose we will assume 
concerning ©; that it satisfies the equation: 
0 
0 Ei yi — — E . . . . . . 
Bor = 5 (T —U—E) (35) 
which contains the unknown quantities ©, and ZE, A second 
equation is therefore required in order to determine them both, for 
which purpose the equation 
y 
Gin= PHU HD) ne eee 
can be used. 
So we find for # the differential equation: 
OF Sn (4) 
OID. Sie ow ee Sone 
A es e? yy e” San? 
sa = — 9, band T+ v=5,(1+45) we find as 
solution of (4) 
