Sensations caused by a Magnetic Field, 191 



by the expression 



H=^(4u-W 1 -VV 2 ), .... (2) 



where N = total number of turns. 



I' = maximum value of current in amperes. 

 1 = length of coil in cm. 



Wi and W 2 = tJ}e solid angles subtended by 

 the ends at any point inside the solenoid. 



For any point p along the axis of the coil, Wj 

 and VV 2 are given by the equations (2) and (3). 



Using the values of a 1 and a 2 as shown in fig. 3, 

 Fiar. 3. 



\7CM- 





57CM 



^\ T l = 2 (1- cos a x ) 

 W 2 = 2 (l-cosa 2 ) 

 2NP 



(3) 



H = ^^ (cos a x + cosa 2 ). ... (5) 



Since the ammeter gives effective values, the maximum 

 current can be obtained from Table I. by the factor \/~2. 



F=V2l (6) 



tt V2 NI , 



H= — ?j (cos a!— cosa 2 )« ... (7) 



From this equation the value of H was calculated for a 

 series of positions along the axis of the coil ; and the results 

 were plotted, as shown in fig. 4 (PL IV.). 



The zero of the abscissa? was taken at the lower end of the 

 coil and the distance shown in the curves of fig. 8 (PL III.") 

 extends to the middle of the coil. The amperes noted on 

 the several curves are the effective values as recorded in the 

 tables. H is the maximum value of field strength per sq. cm. 

 along the axis. 



