ricity from the cat's skin to the gutta percha, or by
a flow of negative electricity in the opposite direction, for these
statements are identical.

In case of our gas cylinders, the gas tends to leak out of the vessel
where the pressure is great into the vessel where it is small. The
heat tends to leak out of a body of high temperature into the colder
one, or the cold tends to go in the opposite direction. Similarly, the
plus electricity tends to flow from the body having a high potential,
to the body having a low potential, or the minus electricity tends to
go in the opposite direction.

* * * * *

[ENGINEERING.]

THE HYDRODYNAMIC RESEARCHES OF PROFESSOR BJERKNES.

BY CONRAD W. COOKE.

[Illustration: FIG. 1.]

We have in former articles described the highly interesting series
of experimental researches of Dr. C. A. Bjerknes, Professor of
Mathematics in the University of Christiania, which formed so
attractive a feature in the Electrical Exhibition of Paris in 1881,
and which constituted the practical development of a theoretical
research which had extended over a previous period of more than twenty
years. The experiments which we described in those articles were,
as our readers will remember, upon the influence of pulsating and
rectilinear vibrating bodies upon one another and upon bodies in their
neighborhood, as well as upon the medium in which they are
immersed. This medium, in the majority of Professor Bjerknes earlier
experiments, was water, although he demonstrated mathematically, and
to a small extent experimentally, that the phenomena, which bear so
striking an analogy to those of magnetism, may be produced in air.

Our readers will recollect that in the spring of 1882 Mr. Stroh, by
means of some very delicate and beautifully designed apparatus,
was able to demonstrate a large number of the same phenomena in
atmospheric air of the ordinary density; and about the same time
Professor Bjerknes, in Christiania, was extending his researches to
phenomena produced by a different class of vibrations, namely, those
of bodies moving in oscillations of a circular character, such, for
example, as a cylinder vibrating about its own axis or a sphere
around one of its diameters; some of these experiments were brought
by Professor Bjerknes before the Physical Society of London in the
following June. Since that time, however, Professor Bjerknes, with the
very important assistan