apparatus for producing
the hydrodynamic analogue of electric currents, in which a conductor
transmitting a current of electricity is represented by a cylinder to
which oscillations in circles around its axis are given by suitable
mechanical means, so as to cause the enveloping medium to follow its
motion and make similar rotative vibrations. In some of the earlier
experiments in this direction, cylinders carrying radial veins (A,
Fig. 2) or fluted longitudinally around their surfaces (B, Fig. 2)
were employed with the object of giving the vibrating cylinder a
greater hold of the liquid in which they were immersed; but it was
found that these vanes or flutings had but little or no effect upon
water or liquids of similar viscosity, and Professor Bjerkes was led
to adopt highly viscous fluids, such as Glycerin or maize sirup, both
of which substances are well adapted for the experiments, being at the
same time both highly viscous and perfectly transparent and colorless.
In seeking, for the purpose of this research, a fluid medium which
shall possess analogous properties to the luminiferous ether, or
whatever may be the medium whose vibrations render manifest certain
physical phenomena, it might be considered at first sight that
substances so dense as glycerin and sirup could have but little in
common with the ether, and that an analogy between experiments made
within it and phenomena associated with ethereal vibrations would be
of a very feeble description: but Professor Bjerknes has shown that
the chief requisite in such a medium is that its viscosity should be
great, not absolutely, but large only in proportion to its density,
and if the density be small, the necessary viscosity may be small
also. Neither is it necessary for the fluid medium to possess great
internal friction, but what is necessary to the experiments is that
the medium shall be one which is readily set into vibration by the
action of the circularly vibrating cylinder; this property appears to
be possessed exclusively by the more viscous fluids, and is, moreover,
in complete accord with what is known of the luminiferous ether
according to the theory of light.

The property is rather a kind of elasticity, which ordinary fluids
do not possess, but which facilitates the propagation of transverse
vibrations.

One form of apparatus for the propagation of rotative oscillations is
shown to the left of Fig. 3, and consists of a cylinder, A, mounted on
a tubul