328 MM. L. Pupin—Studies in the Hlectro-magnetic Theory. 
Let these paths be such that at any moment the total ficti- 
tious electric transference through any elementary area up to 
that moment is equal to the electric flux through that area at 
that moment. Then, as long as we remember that we are 
speaking of a fictitious “integral current” and a fictitious 
“electric displacement” through any elementary area in an 
electric field, we can employ these two terms as synonymous 
with “electric flux” thr ough that area without departing from 
the views of the pre-Maxwellian period. 
Again just as the electric current through any elementary 
area of a conductor is defined as the rate of variation of the 
integral current, so we can also speak of a current through the 
dielectric without deserting the views of old electro-magnetic 
theories provided that we take it as granted that this dielectric 
current is fictitious, since it is the rate of variation of a fictitious 
integral current. The expression “dzelectric or displacement 
current” becomes, therefore, synonymous with rate of varia- 
tion of the electric flux. Similarly we can substitute the 
expression magnetic current for the expression ‘rate of varia- 
tion of magnetic flux.” 
To distinguish the real, that is the electric conduction cur- 
rent, from the fictitious or displacement current, the expression 
“ conduction current” must be used when the real and not the 
fictitious (displacement) current is meant. 
This precaution is unnecessary in the case of the magnetic 
current, since there is no magnetic conduction current. 
The laws of magneto-electric and of electro-magnetic induc- 
tion can now be stated more symmetrically, as follows :— 
First law:—A region of magnetic ..... currents induces 
a field of electric force an all electric conductors within that 
region. The electromotive force around any simple circuit in 
this induced electric field is proportional to the magnetic 
sie Dav hei. current passing through any area which is bounded 
by this circuit. 
Second law:—A region of electric conduction currents in- 
dnees@ field ormacnetic force ia a eee The magneto- 
motive force around any simple circuit.in this induced magnetic 
field is proportional to the electric conduction current passing 
through any area which is bounded by this circuit. 
The formal resemblance between the two laws is very strik- 
ing now. It would be perfect if we either omitted the words 
which are in italics or filled out suitably the dotted lacune. 
The last alternative is not admissible, because we know 
nothing about magnetic conduction currents, nor about mag- 
netic conductors. The first alternative does not strike one so 
unfavorably. There is really no evidence against the permissi- 
bility of omitting the words in italics from the statement of the 
