Page:Popular Science Monthly Volume 36.djvu/641

Rh of alcohol and water of exactly the specific gravity of oil. Into the midst of this liquid he quietly introduced oil by means of a funnel. The oil lay passive between the equal downward pull of gravity and the upward lift of the alcohol and water. In this way the forces which bound the oil particles together had free play. The oil rounded itself at once into a sphere. For a time there was, of course, some chemical action between the oil sphere and the surrounding liquid; but, in making his observations, Plateau waited till these affairs had been settled between them, and their relations became fixed.

He then introduced into his oil sphere a rod, with a disk smaller in circumference than the oil sphere about it. Both of these were well oiled, and they entered the sphere without disturbing it. The globe of oil hung in the water, with the rod running through it in the position of the earth's axis, and the disk almost reaching to the line corresponding with our equator (Fig. 5).

By means of a handle the rod was turned, at first slowly, then gradually and steadily faster. The oil sphere slipped more easily around in its water socket than it would around the revolving rod and disk, and therefore turned upon its own axis. By varying his experiments, revolving his rod faster or slower, Plateau made a miniature representation of a world revolving about its own axis; he made his oil sphere throw off satellites, which revolved about the central sphere; he also, by what he calls a trick, imitated Saturn with its attendant ring.

He followed these experiments by using outlined frames of wire, such as we used for our soap films. These he adjusted around his hanging sphere of oil, and with a syringe withdrew the oil, making first a cube of oil with unsupported faces; and finally, as more and more oil was withdrawn, there resulted a system of oil films, each face of which was in contact with the water, exactly like those in Figs. 1 and 2.

This was the manner in which such systems of films were first reached; and, historically, the experiments have an interest in their relation to the subject of films as well as for the proof they offer that the material of which the films are formed has nothing to do with the forms they take on. Plateau went on from his oil