XX
315
LIGHT AND ELECTRICITY
perfect fluid.
These two statements together land us in a
painful and unintelligible contradiction, which disfigures the
otherwise beautiful development of optics. Instead of trying
to conceal this defect let us turn to electricity; in investigat-
ing it we may perhaps make some progress towards removing
the difficulty.
What, then, is electricity? This is at once an important
and a difficult question. It interests the lay as well as the
scientific mind. Most people who ask it never doubt about
the existence of electricity. They expect a description of it
—an enumeration of the peculiarities and powers of this
wonderful thing. To the scientific mind the question rather
presents itself in the form-Is there such a thing as elec-
tricity? Cannot electrical phenomena be traced back, like all
others, to the properties of the ether and of ponderable
matter? We are far from being able to answer this question
definitely in the affirmative. In our conceptions the thing
conceived of as electricity plays a large part. The traditional
conceptions of electricities which attract and repel each other,
and which are endowed with actions-at-a-distance as with
spiritual properties-we are all familiar with these, and in a
way fond of them; they hold undisputed sway as common
modes of expression at the present time. The period at
which these conceptions were formed was the period in which
Newton's law of gravitation won its most glorious successes,
and in which the idea of direct action-at-a-distance was
familiar. Electric and magnetic attractions followed the
same law as gravitational attraction; no wonder men thought
the simple assumption of action-at-a-distance sufficient to
explain these phenomena, and to trace them back to their
ultimate intelligible cause. The aspect of matters changed in
the present century, when the reactions between electric
currents and magnets became known; for these have an
infinite manifoldness, and in them motion and time play an
important part. It became necessary to increase the number
of actions-at-a-distance, and to improve their form. Thus
the conception gradually lost its simplicity and physical
probability. Men tried to regain this by seeking for more
comprehensive and simple laws-so-called elementary laws.
Of these the celebrated Weber's law is the most important