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 tubular 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_.