ce of his son, Mr. Vilhelm Bjerknes, has been
extending these experimental researches in the same direction, and
with the results which it is the object of the present series of
articles to describe.

[Illustration: FIG. 2.]

The especial feature of interest in all Professor Bjerknes experiments
has been the remarkably close analogy which exists between the
phenomena exhibited in his mechanical experiments in water and other
media and those of magnetism and of electricity, and it may be of some
interest if we here recapitulate some of the more striking of these
analogies.

(1.) In the first place, the vibrating or pulsating bodies, by setting
the water or other medium in which they are immersed into vibration,
set up in their immediate neighborhood a field of mechanical force
very closely analogous to the field of magnetic force with which
magnetized bodies are surrounded. The lines of vibration have
precisely the same directions and form the same figures, while at the
same time the decrease of the intensity of vibration by an increase of
distance obeys precisely the same law as does that of magnetic
intensity at increasing distances from a magnetic body.

(2.) When two or more vibrating bodies are immersed in a fluid, they
set up around them fields of vibration, and act and react upon one
another in a manner closely analogous to the action and reaction of
magnets upon one another, producing the phenomena of attraction
and repulsion. In this respect, however, the analogy appears to be
inverse, repulsion being produced where, from the magnetic analogy,
one would expect to find attraction, and _vice versa_.

(3.) If a neutral body, that is to say a body having no vibration of
its own, be immersed in the fluid and within the field of vibration,
phenomena are produced exactly analogous to the magnetic and
diamagnetic phenomena produced by the action of a magnet upon soft
iron or bismuth, its apparently magnetic or diamagnetic properties
being determined by the specific gravity of the neutral body as
compared to that of the medium in which it is immersed. If the neutral
body be lighter than the medium, it exhibits the magnetic induction of
iron with respect to polarity, but is nevertheless repelled; while
if it be heavier than the medium, its direction is similar to that of
diamagnetic bodies such as bismuth, but on the other hand exhibits the
phenomena of attraction.

In this way Professor Bjerknes has been able to