1058 
in the sense described in $ J, and is determined by the equations 
of EINSTEIN 
Ruy = 5 Om = BE 8 rx Dap, . . . . . (10) 
in which Zw, is a tensor of the second order, which depends only 
on the g’s and their derivatives: 
ey 
0 0 (uv 
“Sich 
mol © o\ le 
while R=g” R,,. x is the gravitation constant of Einstein, which, 
if we choose the gram as unit of mass, is equal to 7,4.10—%9. If 
we assume that the g,,’s of the line-element which corresponds to 
the field of gravitation, only differ little from ¢,,, there exists a 
simple method indicated by Einstein to obtain in first approximation 
a solution of the equations (10). This solution is obtained by writing 
Duy = Evy + Yur Sy, guar” VE teal elgmmees (11) 
where the functions y,, everywhere possess a very small value, and 
introducing the quantities y',, defined by 
no ur} (96 
a 
5] 
o o 
N 
Vues = Yu — 4 Evy (E28 Yup) 
which give 
Vm = Ym — 4 Ee (Exp Yass. « + - » « (12) 
the values of the y',, in the point w,, 2,, @, and at the moment 
v, may be calculated as retardated potentials by means of the 
formulae 
TEN wv — 7 — Pr 
Maun = TT tn f l ed : | dS s = . 5 (13) 
i 
Here dS represents the space-element de, dv, de, and r represents 
the distance from that space-element to the point 
Ly, Les LX, (7? = (x, — z,)* + @, — 4) + @, — 2,)’). 
The addition [,—=.2,—7] means that everywhere the value of 
T.,, at the moment x, —7 has to be used. If we apply the formulae 
(13) to our case where the 7’,,’s do not depend on the time, we 
may clearly omit the latter condition, and we obtain the usual 
formulae for static potentials 
Palas 
7 
We will now calculate the components of the rotation-vector in 
the point w,,2,,2,. Neglecting small terms which relative to the 
main terms are of the same order of magnitude as the y’,,’s, we 
obtain for the w,-component of the rotation-vector 
