the attitude taken by Newton in
connection with gravitation: "In the first place to observe facts, to
vary the circumstances of these as much as possible, to accompany this
first work by precise measurements in order to deduce from them
general laws founded solely on experiment, and to deduce from these
laws, independently of all hypotheses on the nature of the forces
producing the phenomena, the mathematical value of these forces--that
is to say, the formula representing them. Such was the system pursued
by Newton. It has, in general, been adopted in France by the scholars
to whom physics owe the great progress made of late years, and it has
served as my guide in all my researches on electrodynamic
phenomena.... It is for this reason that I have avoided speaking of
the ideas I may have on the nature of the cause of the force emanating
from voltaic conductors."

Thus did Ampere express himself. The illustrious physicist rightly
considered the results obtained by him through following this wise
method as worthy of comparison with the laws of attraction; but he
knew that when this first halting-place was reached there was still
further to go, and that the evolution of ideas must necessarily
continue.

"With whatever physical cause," he adds, "we may wish to connect the
phenomena produced by electro-dynamic action, the formula I have
obtained will always remain the expression of the facts," and he
explicitly indicated that if one could succeed in deducing his formula
from the consideration of the vibrations of a fluid distributed
through space, an enormous step would have been taken in this
department of physics. He added, however, that this research appeared
to him premature, and would change nothing in the results of his work,
since, to accord with facts, the hypothesis adopted would always have
to agree with the formula which exactly represents them.

It is not devoid of interest to observe that Ampere himself,
notwithstanding his caution, really formed some hypotheses, and
recognized that electrical phenomena were governed by the laws of
mechanics. Yet the principles of Newton then appeared to be
unshakable.

Faraday was the first to demonstrate, by clear experiment, the
influence of the media in electricity and magnetic phenomena, and he
attributed this influence to certain modifications in the ether which
these media enclose. His fundamental conception was to reject action
at a distance, and to localize in the