M. I. Pupin—Studies in the Hlectro-magnetic Theory. 329 
first law. It is true that Faraday’s experiments, by which he 
discovered that law, prove the existence of no other induced 
electromotive forces excepting those which Faraday detected 
in conductors. But these experiments neither affirm nor do 
they deny the presence of magneto-electric induction in dielec- 
tries. On the other hand, Faraday’s experiments on dielectric 
and diamagnetic substances and his speculative views of elec- 
tro-magnetic phenomena urge us with an irresistible force to 
the belief that electromotive forces just like magnetomotive 
forces are induced around every circuit, no matter whether that 
circuit pass through a conductor or through a dielectric (inelud- 
ing the most perfect of all dielectrics, that is a perfect vacuum), 
and that just as the magnetic displacement current is real in the 
sense that it produces inductive effects, so the electric displace- 
ment current is not a fiction, as one whois faithful to the views 
of older electric theories has to assume, but it is just as real as the 
electric conduction current in the sense that it is an actually exist- 
ing process in the dielectric, which is just as capable of induc- 
ing magnetomotive forces as the conduction current. The 
mechanism of this process is, of course, just as unknown to 
us as the mechanism of that process which is called the electric 
conduction current. Maxwell was the first to feel the force of 
this tendency of Faraday’s experiments and speculations and to 
yield to it, making thus a radical departure from the views of 
old electric theories. His statement of the two laws of induc- 
tion omits, therefore, the words which are in italics in the last 
statement of these laws. Hence the following wording of 
these two laws is in accordance with Maxwell’s views :— 
First law :—LHvery magnetic current induces a field of elec 
tric force. The electromotive force around any simple corcurt 
in this induced electric field is proportional to the magnetic 
current passing through any area which is bounded by this 
circuit. 
Second law :—Lvery electric current induces a field of mag- 
netic force. The magnetomotive force around any simple 
circuit in this induced magnetic field is proportional to the 
electric current passing through any area which rs bounded 
by this circuit. : 
In this generalized form these two laws form the foundation 
of Maxwell’s electro-magnetic theory.* This theory may, there- 
fore, be described broadly as that theory which generalizes the 
two experimental laws of magneto-electric and of electro-mag- 
netic induction by extending the region of magneto-electric 
induction and of the electric current from conductors to the 
dielectric. | 
® See O. Heaviside, Phil. Mag., February, 1888; H. Hertz, Wied. Aun., xxiii, 
p. 84, 1884; xl, p. 577, 1890. 
