m and m_1 could be brought to any degree of incandescence by passing
the discharges of Leyden jars around the coil C. In such bulbs with
two buttons a very curious effect is produced by the formation of the
shadows of each of the two buttons.

Another line of experiment, 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