ON THE FORCE OF EFFECTIVE MOLECULAR ACTION; AND THE MECHANICAL PROPERTIES AND LAWS DEPENDENT ON IT. By WILLIAM A. NORTON, of New Haven, Conn.

[ABSTRACT.]

THIS paper is, for the most part, a connected review of several topics discussed in former papers published in the American Journal of Science. It was read by title only.

ON A SIMPLE DEVICE FOR PROJECTING VIBRATIONS OF A LIQUID FILM WITHOUT A LENS. By H. S. CARHART, of Evanston, Ill.

SEDLEY TAYLOR'S Phoneidoscope, for obtaining vibrations in a liquid film, employs a horizontal film, and conveys the vibrations to an enclosed mass of air by means of a rubber tube and a funnel. In this case the figures obtained are viewed directly without projection.

Before the publication of Mr. Taylor's method in "Nature," March 28, 1878, I had already succeeded in obtaining projections of such sound-figures by means of the lantern. A tin tube, five centimetres in diameter, was closed at one end with parchment, and at the other with a film of soapy water strengthened with glycerine. This film was held obliquely in the light in front of the lantern condenser; a lens in the path of the reflected beam formed an image of the film crossed with colored bands. The vibrations of the voice, taken up by the parchment, are communicated to the enclosed air and thence to the film. This method possesses the very important advantage of not disturbing the film with the breath, as in the case of a tube open next to the mouth. Accident led to a simplification of this method when sunlight is used. The simplest apparatus that will effect the desired object is most serviceable in illustrating science. I do not hesitate,

1 See Journal of Science, March, 1879, May and June, 1879.

therefore, to present this very simple instrument, designed to project on a screen by means of sunlight, the sound-figures in a liquid film produced either by the voice or by an organ-pipe. No lens or mirror is employed, the film being made to project an image of itself. With sunlight directed horizontally into a window by means of a porte-lumière, the instrument contains in itself all that is necessary for projection.

A short, thick tube of wood is furnished at one end with a telephone mouth-piece and ferrotype plate; the other end has attached to it a funnel about ten centimetres in diameter, blackened within and without. Near the middle of the tube a stop-cock is inserted. A film is obtained in the open funnel in the usual way, and is then slightly distended by blowing air into the enclosure through the stop-cock. The stop-cock being closed, the apparatus is air-tight, and the film retains a nearly constant curvature. This convex film, held in the beam of light at the proper angle, causes the reflected rays to diverge and produces a greatly enlarged image of itself on the screen. The degree of magnification is completely under control, since it is dependent on the curvature of the film. If the curvature has been made too great, the contractile power of the film, due to its surface tension, may be made to expel some of the enclosed air through the open stop-cock.

Upon singing a sustained note at the mouth-piece, concentric circles, distorted into ellipses by oblique projection, appear upon the screen. These can be kept sufficiently steady to permit of photographing them. Two photographic negatives were taken from the screen on which the projections were made. One of them exhibits clearly what I have not been able to make out on the screen, viz. :—a division of the film into segments with indistinct nodal lines radiating from the centre, like the nodal lines on a circular plate of glass clamped at its centre.

When

By placing a cap provided with a rubber band, and having a square opening made in it, into the open end of the funnel, a film of different shape is obtained. It is then observable that only notes of a definite pitch at the mouth-piece agitate this film in a welldefined manner; that is, produce in it "stationary waves." a definite configuration is obtained, it is found to consist of a reticulated pattern of lozenge-shaped figures. Bright points are noticeable at every other intersection of the lines, appearing like knots tied in the interlaced cords of a net. Organ pipes produce