B 
=H) en 
and on this the proof of the second theorem is bascd. 
Now we have for the potential in a point : 
w= lep (r)dr + = Jo g(r) ds 
| 
| 
B 
Now pj (r)=—- +v. So also: 
(te 
‘Bu d Bod 
v=zf Da zt ovdr + = |ovds. 
If we apply to both members the operation y° we find in a 
similar way as we did when proving the preceding theorem: 
Vy = tret fever Cy ode 7am 
Now we get in consequence of (7): 
zfevvar= "2 fer dr 
and in the same way: 
zfe ved fz fon ds 
or 
5 eVedr +3 ford (2 eg ,dt+= opde \=— oy 
Equation (8) becomes: 
Viw=—4nBo-—Py 
or because B= A sina: 
ws gp An Ana ys {I 
Let us now prove the reversed theorem of Theorem I). 
*) With that modification that B is put 0. 
