THE

ON THE FORCE OF EFFECTIVE MOLECULAR ACTION; AND 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.

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." When 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

these figures with more certainty and definiteness than the voice. With a triangular opening in the cap, the distended film is too much distorted from the spherical form to yield a clear image. In this case, with a flat film a lens may be employed to obtain the image. Let a clear musical note then be sung near the mouthpiece of the apparatus; immediately the field of color is covered with an exquisite pattern of fixed, hexagonal figures, the colors presenting at the same time the appearance of flowing, sometimes irregularly and sometimes around fixed centres. With a clear, sustained note, nothing can exceed the beauty of this combined acoustic and chromatic display.

NOTE ON THE ZODIACAL LIGHT. By HENRY CARVILL LEWIS, of Germantown, Pa.

[ABSTRACT.]1

THE results of a series of observations, made by the writer, upon the zodiacal light extending over a period of nearly five years, are here recorded. The special precautions taken, both to train the eye to detect faint lights, and to prevent bias on the part of the observer, are given in detail.

The zodiacal light is divided into three portions-the zodiacal cone; the zodiacal band; and the gegenschein. This division is convenient in observation, saves confusion in description, and may be in part a natural one.

The zodiacal cone.-This, the zodiacal light proper of most authors, is the well-known cone of light rising along the ecliptic, and best seen in the winter months in the west, immediately after the disappearance of twilight. The time of shortest twilight coincides with its greatest brilliancy. Several observations are given when the writer saw it cast a distinct shadow at that time. Its comparative brightness with the Via Lactea at different seasons are given, and its relation to the ecliptic discussed. It was stated that the cone in our latitude is not symmetrical; and that while its

1 Published in full in Amer. Jour. Sc. and Arts, December, 1880. A. A. A. S., VOL. XXIX.

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axis of greatest brightness lies exactly upon the ecliptic, its axis of symmetry is north of that line. An inner short cone of greater brightness was described. The warm color was thought to be due to atmospheric absorption. No pulsations were ever observed which could not be explained either by atmospheric changes or by changes in the eyesight of the observer. No periodic changes in the zodiacal light were observed; the same series of changes occurring each year with an equal amount of brilliancy. It was shown that while the zodiacal cone is frequently seen by moonlight, the moon appears to have no appreciable influence upon it. The account of the zodiacal cone closes with a description of its spectrum, which is always continuous and free from bright lines.

The zodiacal band. - This is an extremely faint zone of light, somewhat wider than the Via Lactea, which, like a strip of gauze, is stretched across the sky along the zodiac from horizon to horizon, and which can be seen at all times. It is a belt which forms a very faint prolongation of the zodiacal cone, and which, like it, is best seen when the ecliptic makes a large angle with the horizon. It is so faint. that it can only be seen with difficulty. It is brightest along an inner line, and fades off more suddenly on its southern than on its northern edge. It has a width of about 12°, and its central line is slightly north of the ecliptic. Observations prove the zodiacal band to be a constant and invariable phenomenon. The gegenschein.-The gegenschein is a faint patch of light, apparently some 7° in diameter, which nightly appears in that part of the zodiacal band which is 180° from the sun. Night after night it shifts its place so as to keep opposite to the sun. It is decidedly brighter than the zodiacal band, and frequently a central nucleus about 2° in diameter, of greater brightness, can be observed. While the brighter portion of the gegenschein is circular, its faint boundaries have sometimes the form of an oval, whose major axis is parallel to the ecliptic. A large number of maps of its position among the stars have been made, which show that while its central point is always 180° in longitude from the sun, it has a latitude of +2°.

The moon zodiacal light.--An oblique cone of light in the proximity of the moon was described by Rev. G. Jones, but has not been detected by the writer. The light preceding moonrise rises at right angles to the horizon, and seems purely atmospheric. One observer has described comet-like tails on either side of the moon.

The writer holds that such appearances are caused by diffraction through floating vapor, since they are not seen on clear nights.

The horizon light.-The phenomenon to which this name is applied, though having no connection with the zodiacal light, is so continually observed with the latter, and at certain seasons is so apt to be confounded with portions of it, that it is necessary to take it into account. The horizon light is a faint band of light with parallel sides, lying all around and parallel to the horizon, and separated from it by an interval of darkness. It is brightest and terminates most abruptly, on its lower edge. This sharp lower edge is 5° above the horizon, while the diffuse upper edge varies in altitude with the state of the atmosphere. The horizon light has a mean width of about 15°. It is purely atmospheric and appears. to be caused by reflected starlight. It becomes very bright when the moon is above the horizon. Below the horizon light is a dark space, here called for convenience, the absorption band. This quenches the light of the Via Lactea, the zodiacal cone, and all but the largest stars and planets. When the ecliptic is low, the horizon light frequently blends with the zodiacal band.

THE AURORA AND ZODIACAL LIGHT OF MAY 2, 1877. By HENRY CARVILL LEWIS, of Germantown, Pa.

ALTHOUGH the Aurora of May 2, 1877, as seen from Germantown, Pa., was not a remarkable one, either for brilliancy or for beauty of coloring, yet special interest is attached to it from the fact that it was seen in conjunction with the Zodiacal Cone, and direct comparisons could be made between the two phenomena.

No auroras had been noticed for several years previously, it being a period of minimum auroral intensity. The aurora was first observed at 8.35 P. M., when it was brighter than at any subsequent time. It then consisted of a bright, nebulous mass of light along the northern horizon, arched above, extending from Auriga to Cygnus. Polaris was over about the centre of this