Crook — Electromagnetic Alternating Cicrrents. 145 



should expect the values of any point on curve 4 to be one- 

 half that of a similar point on curve 3. Any added effect 

 caused by the presence of the electric flow in the iron would 

 tend to make curve 3 approach curve 4, and in fact it is found 

 that the latter falls below the former. 



If the apparatus used in the second method was as effectual 

 in reducing the circular magnetic effects as was expected, 

 curve 1, Diagram lY, can be taken as giving an approximate 

 measure of the reduction of the residual magnetism by an alter- 

 nating current flux, with a frequency of 133 alternations per 

 second ; and curve 1, Diagram Y, a similar measure when the 

 frequency is at QQ alternations per second. The effect of the 

 magnetically compensated current as given by these curves 

 is about one-fourth of the total effect of the current and 

 circular magnetic effect together. 



Other Methods. 



The following experiments were made to study the effects 

 of electric oscillations on magnetized plates (fig. 3 A) placed 

 in a magnetizing solenoid of very thin sheet iron (trunk cover- 

 ing) cut into strips 7 inches X3/4: inch and separated by sheets 

 of mica made to project past the edges of tbe iron an eighth of 

 an inch. This system was connected to a Holtz machine and 



Fig. 3. 



-O o- 



the spark gap adjusted so as to get a rapidly oscillating dis- 

 charge. The magnet, after being magnetized to a maximum 

 amount of residual magnetism, was placed carefully in the 

 field of a sensitive magnetometer. This magnetometer was 

 made of an astatic magnetic system suspended by a silk fiber 

 in a glass tube. The magnet was so placed that the mag- 

 netometer was defiected a few degrees from the meridian. 

 The system was carefully tested to prove the effect produced 

 was not due to conditions external to the iron. Any disturb- 

 ance in the magnetic field of force thus produced could be 



