408 Dr. A. D. Fokker on the Electric Current from 

 x a + ^ x a w jth respect to x a : 



B (% a +• Ax a ) ~d(x a + Ax a ) 



~dx a 'dx b 



d (x h + A# 5 ) dQ 6 + A^) 

 B# & 



(dYdty 



~dx a 



or, consistently neglecting 2 



1 + 



d# a 



d# a 



1 + 



3r a 

 ~bx h 

 ~dr b 



B^ 



dVtft. 



-■[i+s(^g]rfv*; 



dV d*i 



Thus we find after the displacement the sum of the 

 individual components described per unit of volume per unit 

 of time to be : 



N«.« + AN«^= [Nw*+2(&)N«m|^] . [l-S(&)0g^], 



Now it must be borne in mind that this value of the new 

 stream-component is found in the point-instant x a -\-^x a and 

 not in the point-instant x a , where we wanted to know it. To 

 obtain the latter value we obviously ought to choose our 

 starting-point in the point-instant x a — 0r a , and take 



instead of ~Niv a . Thus we find, availing ourselves of the 

 equation of continuity (2) also : 



} -)'a"NT7«6_r 6 Nw a f , 



and the first variation is 



]$w« + 8Nw" = ~8w« + '2(b)0-^- s l r*ls 



SNto« = 2(6)0^|^Nio6-r»Nio«|. . . (3) 



