On Eapid Periodic Variations of Terrestrial Magnetism. 



55 



to GO , 7i being kept constant, while JX,„ increases indefinitely 

 with b. The ratio AZjAX,,, tends to 1/2 when b decreases 

 indefinitely, as is already evident from the former results. 



d) Let a number of such currents be arranged with the 

 directions alternately positive and negative, and parallel to each 

 other at definite intervals, eacli moving perpendicular to itself 

 witli a uniform velocity. Neglecting the effect of the induced 

 current, the magnetic field at A will undergo a train of periodic 

 variation as illustrated in the annexed figure (Fig. 20) for a special 



h-b- I 



Fig. 20. 



Viilnnct, . - X = 6 



Positiue Ciiyy^nt oX 

 Negoliue Currenï at 



case. As will Ije seen, the phase retardation of AZ is somewhat 

 similar to that in the actual case, though here at the same time 

 with the short waves, a rather remarkable general swelling of 

 the curves appears. The latter may probably be avoided ])y 

 properly reducing the intensity of the currents toward both ends 

 of the train. In this case, the pulsations must necessarily be 

 progressive. 



23. Next, we will consider the effect of the current induced 



