Page:Popular Science Monthly Volume 35.djvu/624

 by different investigators to reside in the thin envelope of the water-drop; acoustic energy by M. Savart, as noticed in a cascade of water-drops, the envelopes of which underwent rhythmical deformations; calorific energy, due to the displacement of molecules that pass from the surface to the ranks, or which ascend to the superficial layer; luminous energy, as studied by Newton, Boyle, Hooke, Young, and Fresnel; and electrical energy, as manifested in effects that have been observed by M, Lipmann—all of which, according to M. Gossart, are transformable one into another in accordance with the law of conservation of force. A drop of water hangs from a leaf or the eaves of a house, held up as in a bag by its superficial envelope. It continues to increase in size and weight many times faster than the tension of its cordon of attachment is re-enforced, till it overcomes that tension, and then it falls; and, according to M. Gossart, all the drops of water that fall—of themselves—are of the same size. The drops of melted metals, whose superficial tensions are enormous, reach correspondingly enormous magnitude. The purity of liquids can be determined by observing the size of the drops they give; in the case of wines, by counting the number of drops per cubic centimetre; for the superficial tension of all liquids is modified by adulteration.

M. Van der Mensbrugghe has calculated what he calls the potential energy of water, on the basis of the estimation of its superficial tension at 7·5 milligramme-millimetres per square millimetre of free surface. This is resident in a film not more than 1/20,000 of a millimetre thick. Distributed over the whole ocean, it gives an amount of mechanical force which we have no means of accurately calculating. If we suppose that of two equal and adjacent superficial layers of sea-water, one washes over the other by the effect of the wind, for example, the layer that is covered loses its free surface, and with it its proper potential energy, which appears again in an increase of speed. Thus on the ocean the action goes on, the energies of the successive waves being extinguished as to them and transferred to others; so that