1005 
r 
rs == — "fora ee a (7) 
Sod Tee Ay Sa ETE 
0 
if we put 
lor’ dr = a(r). 
- 
0 
oo 
1 te ser Gi: d 
s= r. 
c? er 
: 
Let this approximation of s be called s,. We now go a step 
further, by retaining the terms with x? in p, q, s, and in the equations 
(10). We may put 
Hence 
we 
Wehe Beer 
cr 
We now put 
fas, SG, | 
which makes the third equation (10) pass into 
- d 3 gi 4 Ae 7a? : 
——|rr-—ter nee 
dr Se ; 4 cr? ° 
Now, up to the terms of the first order, 
Ë 3 x “a ee 3x Ca 
SS et he cl 1 a ee aie En fe tee ie 
ad ¢ 2c.) r? 
r 
so that we find 
Ly Acer eT ah Ea we, fa forint. 
— —(er’s) — — — —|r%c*s, |—dr | — = x70, 
dr Cc a dr GT 2e dr ay A4cr? al 
which in consequence of 
passes into 
