on a Permanent Electric Current. 183 
MxV 
EK’ 
not be expected to give the same result for all metals. We 
get the quantity V by dividing the nominal cross section of our 
conductor by the strength of the current. We must, however, 
think of a metal as not strictly continuous, but consisting of 
It is evident, upon consideration, that this ratio could 
conductors of the same nominal cross-section. It may, there- 
fore, be found that different specimens, of the same metal but of 
M 
x 
EK’ 
Of course the magnitude of the new action in the different 
metals may be considered in connection with various other 
physical properties of the metal beside the specific electrical 
resistance. One might for instance expect to find some strik- 
ing relation by comparing in this connection the known mag- 
netic or diamagnetic properties of the metals. It is indeed 
to be observed that the most strongly magnetic substance, 
iron, does show the new action in a more marked degree 
than the other metals, and possibly nickel will come next 
in the list. Here the clue is entirely lost however, for the 
relative magnitude of the action in gold, silver, etc., is entirely 
different densities, will give quite different values for 
se 
metals. It is of course possible, however, that ore 
present unsuspected will appear. It can hardly be doubted 
that the action we have been considering, placing at our com- 
m. 
e return now to the remarkable anomaly presented by 
the direction of the action in iron. That the direction in 
this metal, a magnetic substance, should be different from that 
in gold, a diamagnetic substance, is remarkable, but not per- 
haps surprising. We find, however, that nickel and platinum, 
both magnetic substances, resemble in the particular above 
mentioned, not iron, but gold, and the other diamagnetic sub- 
stances. This fact has to be taken into account in endeavor- 
lug to apply the newly discovered action to explain the mag- 
netic rotation of the plane of polarization in accordance with 
