12 
IOWA ACADEMY OP SCIENCE 
on in the intervening medium; as effects propagated continuously from point 
to point in space. He assumed the existence of lines of force stretching from 
one magnetic pole to the other and from one electrostatic charge to another 
of opposite sign. These lines were real to him, exerting lateral and longi- 
tudinal tension upon each other. The energy of magnetization and electrification 
was not in the ponderable masses, associated with these phenomena, but 
rather in these ether lines of force which stretched out in all directions through 
the invisible surrounding space. His admirable experiments illustrating the 
different specific inductive capacities of various dielectrics were striking cor- 
roborations of his theory. The notion of cutting these invisible lines of force 
when a current is induced in a conductor moving through a magnetic field 
was originated by him. It has been aptly said that Faraday’s theory, which 
is now generally accepted, had the result of brushing the term “the electric 
fluid’’ into the limbo of newspaper science. 
Faraday’s theory was thrown into mathematical form by J. Clerk Maxwell. 
Before taking up the study of electricity Maxwell resolved to read no mathe- 
matics on the subject until he had made a study of Faraday’s researches. 
He knew that there was a great difference between Faraday’s way of con- 
ceiving phenomena and that of his European contemporaries. Stated in Max- 
well’s words, “Faraday in his mind’s eye saw lines of force traversing all 
space where the mathematicians saw centers of force attracting at a distance. 
Faraday saw a medium where they saw nothing but distance. Faraday sought 
the seat of the phenomena in real actions going on in the medium; they were 
satisfied that they had found it in a power of action at a distance impressed 
on electric fluids.” 
Maxwell was so impressed with the reality of Faraday’s theory that he at 
once undertook the production of a mathematical discussion of some of its 
salient points. In 1861 he published papers on “Physical Lines of Force,” in 
which he developed the idea that the seat of magnetic energy is in the mag- 
netic field, or rather, the dielectric which surrounds the magnet. The full 
fruition of his work on the Faraday theory appeared finally in his treatise on 
“Electricity and Magnetism” published in 1873 under the caption of the 
“Electro-magnetic Theory of Light.” 
This mathematical discussion of Maxwell’s has been a veritable mine for re- 
search workers ever since. Maxwell, himself, not being a great experimentalist, 
feared there would never be experimental verifications of many of the conclu- 
sions he obtained. When we contemplate what has already been realized, we 
cannot but wonder at the greatness of such a master mind. Silvanus P. Thomp- 
son says in his treatise on “Electricity and Magnetism” that the “Electro- 
magnetic Theory of Light” is the greatest achievement of the Nineteenth Cen- 
tury. This is hardly an exaggeration in the light of present attainments based 
on this theory. 
MaxY^ell’s mathematical discussion of the Electro-magnetic Theory of Light 
is based on a set of fundamental equations commonly termed “Maxwell’s 
Equations.” These equations assumed the possibility of the production of 
vibrating displacement currents of electricity in free space, or in any dielectric. 
Furthermore, they assumed that the displacement currents were accompanied 
by magnetic displacements in a direction at right angles to the former. These 
