ar spindle, and which is set into circular oscillations around
its axis by the little vibrating membrane, C, which is attached to
the axis of the cylinder by a little crank and connecting rod shown
in detail in Fig. 4. This membrane is set into vibration by a rapidly
pulsating column of air contained in a flexible tube M, by which
apparatus is connected to the pulsation pump which was employed by
Professor Bjerknes in his earlier experiments. In Fig. 5, a somewhat
similar apparatus for producing horizontal vibrations is shown, and
marked N H C, the only difference between them being one of mechanical
detail necessitated by the change in the position of axis of vibration
from the vertical to the horizontal.

If circularly vibrating cylinders, such as we have described, be
immersed in a viscous fluid and set into action, the following
phenomena may be observed: 1. The effect upon the fluid itself,
setting up therein a field of vibration, and corresponding by analogy
with the production of a field of force around a wire conveying an
electric current. 2. The effect upon other circularly vibrating bodies
within that field of force corresponding to the action and reaction
of electric currents upon one another. 3. The effect on pulsating and
oscillating bodies similarly immersed, illustrating the mutual effects
upon one another of magnets and electric currents. The first of these
effects is one of induction, and, from what has been said from an
earlier part of this article, it will be understood that the analogy
between the hydrodynamic and the electric phenomena is direct and
complete. The effects classified under the second and third heads,
being phenomena of direct action (in the restricted use of the word),
are uniformly analogous to the magnetic and electric phenomena which
they illustrate.

(_To be continued._)

* * * * *

THE XYLOPHONE.

Like most musical instruments, the xylophone, had its origin in very
remote times. The Hebrews and Greeks had instruments from which the
one of to-day was derived, although the latter has naturally undergone
many transformations. Along about 1742 we find it widely in use in
Sicily under the name of _Xylonganum_. The Russians, Cossacks, and
Tartars, and especially the mountain population of the Carpathians
and Ural, played much upon an instrument of the same nature that they
called _Diereva_ and _Saloma_.

It appears that the xylophone was p