Here still another, which by my fingers' touch casts a shadow--the
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