PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 687 



here /(r) is a continually positive function of r. Let us now see what are the consequences to which 

 u's will lead. 



Equation (I) may now be written 



vdv = -., dr f(r) dr , 

 hence we obtain 



V ~ _L I" V _L <" 



2 H- 7 == 2" + r !' ( r ) , when F(r) = 



Furtlier 



., drp drr ds 



,id 



dv fi dr f , , dr 



By substitution in equation (II) we then obtain 



, drtPr 



.ds) 



( by multiplying by 



5 

 ds 



Here we will put 



\icnce we obtain 



We then put 



\iereby the equation assumes the form 



dr d*r dx 



= .v and = .v . , 



ds rfs- dr 



m;i i - i - i 



(IV) Z + pi .v + f + z/^r ^ = 



