376 



Dr. P. E. Shaw. The Magnetic 

 TIG. 2. 



[May 22 







iA 



By a well-known formula the magnetic force (AZ), due to the layer 

 QQ' carrying current y, is given by 



l-z l + z 



AZ 



Here 



= 1 \ 



I 



r = a-c + qh, q = 0, 1, . . . 20, 21. 

 Maclaurin's summation formula gives 



- 22 



^2 ^2 



where terms of order f" (a) = . .-/'( a ) have been neglected. 



The total number of ampere turns in the solenoid is 22/ry, and 

 the number per centimetre is 22wy/2/ ; let the magnetic force inside 

 an infinitely long solenoid with the same number of ampere turns per 



47T 2271V 



centimetre be H, then H = ---- 57 ^ = 47rNy. 



Maclaurin's formula gives for the actual magnetic force 

 H [ -^^ { 1 - 0- 



-184 



+ 0-552- 



J y 

 V "f^ *v 



i /"\1 Q A 



( 



Now we have 21 = 19, a = 2-75, c = 1'20, so that 



~ => 0-290, 



0-143, ~ = 0-192. 

 a* 



