, viz., 40 tons per day, but
practice has shown it to be most economical to use coal of the
best quality, costing $5 per ton, making the cost of fuel about
double that required for the electric system. Without entering
into other economies which the speaker claimed were in favor of
electricity, and ignoring the plan suggested by Sir William
Siemens of braking the train by converting the motor into a
dynamo and thus utilizing the energy of momentum, he believed
that the economy in fuel alone was sufficient to prove that the
application of power by electricity was preferable to direct
steam propulsion for the elevated railroad service.

* * * * *

MAGNETISM IN ITS RELATION TO INDUCED ELECTROMOTIVE FORCE AND
CURRENT.[1]

[Footnote 1: A paper read before the American Institute of
Electrical Engineers, New York, May 22, 1889.]

By ELIHU THOMSON.

There is perhaps no subject which at the present time can have a
greater interest to the physicist, the electrician, and the electrical
engineer than the one which heads this paper. The advances which have
been made in the study from its purely theoretical or scientific side,
and the great technical progress in the utilization of the known facts
and principles concerning magnetic inductions, can but deepen and
strengthen that interest.

On the side of pure theory we find the eager collection of
experimental data to be submitted to the scrutiny of the ablest and
brightest minds, to be examined and reasoned upon with the hope of
finding some clew to satisfying explanations, and on the side of
practice we find the search for new facts and relations no less
diligent, though often stimulated by practical problems presented for
solution. Indeed, the urgency for results is often the greater on the
practical side, for theory can wait, practice cannot, at least in the
United States.

We must look for continued triumphs in both directions, and the most
welcome of all will be the framing of a theory or explanation which
will enable us to interpret magnetic and electric phenomena. The
recent beautiful experiments of Hertz on magnetic waves have opened a
fertile region for investigation.

It would seem that the study of magnetism and electricity will give us
the ability to investigate the ether of space, which medium has been
theorized upon at great length, with the result of leaving it very
much whe