Experiments with Alternate Currents of High Potential and High Frequency | Page 5

I take hold of it; I bring my body in contact with a wire
conveying alternating currents of high potential, and the tube in my
hand is brilliantly lighted. In whatever position I may put it, wherever I
may move it in space, as far as I can reach, its soft, pleasing light
persists with undiminished brightness.
Here is an exhausted bulb suspended from a single wire. Standing on
an insulated support. I grasp it, and a platinum button mounted in it is
brought to vivid incandescence.
Here, attached to a leading wire, is another bulb, which, as I touch its
metallic socket, is filled with magnificent colors of phosphorescent
light.
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 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 investigators, to
mention only Spottiswoode and J.E.H. Gordon, have used a rapid break

in connection with the coil. Our knowledge and experience of to-day
enables us to see clearly why these coils under the conditions of the
tests did not disclose any remarkable phenomena, and why able
experimenters failed to perceive many of the curious effects which
have since been observed.
In the experiments such as performed this evening, we operate the coil
either from a specially constructed alternator capable of giving many
thousands of reversals of current per second, or, by disruptively
discharging a condenser through the primary, we set up a vibration in
the secondary circuit of a frequency of many hundred thousand or
millions per second, if we so desire; and in using either of these means
we enter a field as yet unexplored.
It is impossible to pursue an investigation in any novel line without
finally making some interesting observation or learning some useful
fact. That this statement is applicable to the subject of this lecture the
many curious and unexpected phenomena which we observe afford a
convincing proof. By way of illustration, take for instance the most
obvious phenomena, those of the discharge of the induction coil.
Here is a coil which is operated by currents vibrating with extreme
rapidity, obtained by disruptively discharging a Leyden jar. It would
not surprise a student were the lecturer to say that the secondary of this
coil consists of a small length of comparatively stout wire; it would not
surprise him were the lecturer to