he
Crookes shadow, of the stem inside of it.

Here, again, insulated as I stand on this platform, I bring my body in
contact with one of the terminals of the secondary of this induction
coil--with the end of a wire many miles long--and you see streams of
light break forth from its distant end, which is set in violent
vibration.

Here, once more, I attach these two plates of wire gauze to the
terminals of the coil. I set them a distance apart, and I set the coil
to work. You may see a small spark pass between the plates. I insert a
thick plate of one of the best dielectrics between them, and instead
of rendering altogether impossible, as we are used to expect, I _aid_
the passage of the discharge, which, as I insert the plate, merely
changes in appearance and assumes the form of luminous streams.

Is there, I ask, can there be, a more interesting study than that of
alternating currents?

In all these investigations, in all these experiments, which are so
very, very interesting, for many years past--ever since the greatest
experimenter who lectured in this hall discovered its principle--we
have had a steady companion, an appliance familiar to every one, a
plaything once, a thing of momentous importance now--the induction
coil. There is no dearer appliance to the electrician. From the ablest
among you, I dare say, down to the inexperienced student, to your
lecturer, we all have passed many delightful hours in experimenting
with the induction coil. We have watched its play, and thought and
pondered over the beautiful phenomena which it disclosed to our
ravished eyes. So well known is this apparatus, so familiar are these
phenomena to every one, that my courage nearly fails me when I think
that I have ventured to address so able an audience, that I have
ventured to entertain you with that same old subject. Here in reality
is the same apparatus, and here are the same phenomena, only the
apparatus is operated somewhat differently, the phenomena are
presented in a different aspect. Some of the results we find as
expected, others surprise us, but all captivate our attention, for in
scientific investigation each novel result achieved may be the centre
of a new departure, each novel fact learned may lead to important
developments.

Usually in operating an induction coil we have set up a vibration of
moderate frequency in the primary, either by means of an interrupter
or break, or by the use of an alternator. Earlier English