184 Ei. H. Hall—New Action of Magnetism 
the principles of Maxwell’s electro-magnetic theory of light. 
Professor Rowland, therefore, in view of this difference of 
iron, has, in the plate used, unmistakably the same direction. 
This nickel plating, however, was executed in Germany, and 
Professor Rowland thinks that, as the nickel of that country is 
very impure, this specimen may possibly contain iron enough. 
to mask the true action of the nickel. 
I have already spoken of the fact that, when a strongly mag- 
netic substance is experimented upon, complications are intro- 
duced by the influence of the induced magnetism which affects 
the condition of the magnetic field through which the current 
flows, making the value of M different from that determined 
by means of the test coil. It does not seem probable that in 
this fact can be found an explanation of the anomalous behav- 
the electro- magnet would be accompanied by a permanent 
change in the equipotential lines after the electro-magnet had 
to 
