( -<"^ ) 



Let us now approximate l/a„' U — •'') + V 



for small values of x. 

 We shall find : 



:ï'=...|/ 



l-,r4- 



V. '^•' 





n^ /l9 2 /l2S 4 ^ 



«0 l/, multiplied by 2 — .r, yields then : 



2 (1 - ..) + V, -^^ 



let 



1 -«„ 



This, subtracted from (1 + «„'') (1 — x) + V, x\ gives: 



(1 — «„)' , (1 — «oT , 



«0 «0 



If now finally this formula is divided by (i — «„^) (1 — .i'), we get: 

 , .r' (1 + a„y ] 



Equation (5) changes now into : 



1 — 



r[t t. 



Notice, that the term ^vith x does not occur, in consequence of 



which ( — I satisfies the condition of becoming 0. 

 \dx y„ 



If higher powers than .c' are neglected, the above becomes: 



4«„ R\T 1\ 



or also, if we now replace q by Q„ (see above) and TT„ by Ta\ 

 which does not bring about a change in the coefilicient of a.'', as 

 T = T, {l—0x') : 



1\ 



Qo 



4«„ 



(5°) 



which approximate expression holds for not too small values of 

 a (e.g. (( = Vs) at least u[) to values of .r = 0,l. We see, that 

 J\ — r is not proportional to x, for small values of x, but pro- 

 portional to x\ Hence instead of tiie usual straight downward course 



