eriment, which has been assiduously followed, was
to induce by electro-dynamic induction a current or luminous discharge
in an exhausted tube or bulb. This matter has received such able
treatment at the hands of Prof. J.J. Thomson that I could add but
little to what he has made known, even had I made it the special
subject of this lecture. Still, since experiences in this line have
gradually led me to the present views and results, a few words must be
devoted here to this subject.

It has occurred, no doubt, to many that as a vacuum tube is made
longer the electromotive force per unit length of the tube, necessary
to pass a luminous discharge through the latter, gets continually
smaller; therefore, if the exhausted tube be made long enough, even
with low frequencies a luminous discharge could be induced in such a
tube closed upon itself. Such a tube might be placed around a ball or
on a ceiling, and at once a simple appliance capable of giving
considerable light would be obtained. But this would be an appliance
hard to manufacture and extremely unmanageable. It would not do to
make the tube up of small lengths, because there would be with
ordinary frequencies considerable loss in the coatings, and besides,
if coatings were used, it would be better to supply the current
directly to the tube by connecting the coatings to a transformer. But
even if all objections of such nature were removed, still, with low
frequencies the light conversion itself would be inefficient, as I
have before stated. In using extremely high frequencies the length of
the secondary--in other words, the size of the vessel--can be reduced
as far as desired, and the efficiency of the light conversion is
increased, provided that means are invented for efficiently obtaining
such high frequencies. Thus one is led, from theoretical and practical
considerations, to the use of high frequencies, and this means high
electromotive forces and small currents in the primary. When he works
with condenser charges--and they are the only means up to the present
known for reaching these extreme frequencies--he gets to electromotive
forces of several thousands of volts per turn of the primary. He
cannot multiply the electro-dynamic inductive effect by taking more
turns in the primary, for he arrives at the conclusion that the best
way is to work with one single turn--though he must sometimes depart
from this rule--and he must get along with whatever inductive effect
he