Again the electrostatic stress kept constant may by being carried
through space carry with it a wave, just as a moving projectile carries
a wave of air in advance of itself.
Admitting this much the following consequences follow:
Since in non-conductors the displacement produces a restitution force,
which varies as the displacement which is requisite or is a criterion
for the propagation of waves, while in conductors no such force is
manifested and the electric energy appears as heat, it follows that
light vibrations are not possible in conductors, because
electro-magnetic waves do not exist in them when they are in circuit,
and conductors should be opaque, while the reverse is true for
non-conductors. (Daniell.)
This is carried out often enough to make a striking evidence in favor of
Maxwell's theory.
The velocity of propagation of an electro-magnetic disturbance in a
non-conductor should be equal to that of light. This constant is proved
by mathematical considerations, to be approximately the same as the
ratio of the electrostatic to the electromagnetic unit of intensity or
quantity. This ratio is 3E10 (30,000,000,000), which is almost exactly
the velocity of light.
It also follows from what has been said that if an electrostatically
charged body were whirled around a galvanometer needle at the rate of
3E10 revolutions per second it should affect it like a circulating
current. This rate of rotation cannot be attained, but Rowland has made
manifest the effect of a rotating statically charged body upon a
magnetic needle.
The above is the merest outline of Maxwell's theory. The full
development must be studied in his own and succeeding works.
Mayer's Floating Magnets.
An experiment due to Prof. Mayer. A number of sewing needles are
magnetized and thrust into bits of cork, almost all the way through,
with their like poles projecting. They are floated in a basin of water
and take, under the effects of attraction and repulsion, when approached
by a magnet pole, regular geometric positions, marking out the positions
of angles of polygons.
Measurements.
The determination of the value of quantities; determination of the
factor by which the unitary value must be multiplied to produce the
quantity under examination. Such are the measurement of the voltage of a
galvanic battery, or of the ohms of resistance of a conductor.
Electricity has been termed the science of measurement.
Meg or Mega.
A prefix, meaning one million times. A megohm is one million ohms; a
megerg is one million ergs; a megadyne is one million dynes.