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 zodia cal 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.

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 prox imity 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

arch, from all parts of which numerous streamers darted upward toward the zenith.

Meanwhile, the zodiacal cone rose obliquely along the ecliptic, farther west. It was a much less conspicuous object than it had 'been two months before, when twilight was shorter. It was in no way altered from its usual appearance at this season, by the presence of the aurora. The southern edge of the cone was, as usual, better defined and more vertical than the northern edge; while the axis of greatest brightness, corresponding closely with the ecliptic, lay south of the axis of symmetry. Its base was widened out by atmospheric diffraction, and its apex merged into the zodiacal band. It was of about the same pale color as the aurora, having lost the warm color which can be noticed at its maximum of brightness. Unlike the flickering streamer of the aurora, it remained perfectly steady, and showed no fluctuations of brightness. It was bright until about nine o'clock, and then, as its lower portion sunk below the horizon, gradually became more and more faint, until it could be no longer recognized.

The aurora went through a number of changes in detail, although maintaining the same general appearance for more than an hour. An arch, entirely disconnected with the lower arch, would sometimes form completely in a few seconds. This upper arch was composed of a number of very short rays placed laterally one along side of the other; and the arch extended by the addition of more short rays. Sometimes small clouds of light, not unlike cirrus clouds, formed neat the horizon upon the longer rays, without interrupting them. Once an arch composed of short rays, each of which was some 3°-4°, and every fourth or fifth of which was longer and brighter than the others, formed suddenly and simultaneously across the sky, stretching from the zodiacal cone, against which one extremity apparently rested, to a point in Cepheus. New streamers were continually added to it in the east, and the short streamers composing it apparently drifted very slowly westward. At 9.27, this arch disappeared entirely in the course of a few seconds. At 9.34, it was again formed, stretching from Taurus to Cepheus, and consisting as before, of short

rays.

At the formation of each arch, or when a new streamer is shot forth, the nebulous mass of light near the horizon would greatly

1 Note on the Zodiacal Light, by II. C. Lewis. Amer. Jour. Science, December, 1880.

brighten, as though it were a cloud illuminated by flashes of light. The streamers were nearly parallel to one another, their centre of divergence lying below the horizon. They were quite straight, and, unlike clouds, sharply defined on their edges. Often a streamer seemed best defined on the edge nearest the centre of the aurora. At one time, it was thought that a number of the streamers on the eastern half of the aurora were bent over at their upper portions toward the east, as though blown by a wind. The streamers were brighter and higher at the extreme east and west of the aurora, than at its central northern portion. The color of the streamers and of the bank of light below them was pale greenish-white. At first, a few short streamers of a warmer tint were occasionally seen.

At 9.33, the zodiacal cone being now low down towards the horizon, and pointing towards Præsepe, a very remarkable auroral streamer formed low down in the west. It was a bright, short streamer, probably 2° or more in width, which pointed very slightly west of Gemini. It started from near Aldebaran, now below the horizon, passed between 3 and Tauri, and reached Auriga between x and 0. It was thus close to the edge of the zodiacal cone.

This streamer remained in the same position for nearly an hour. It was remarkably steady, and was not unlike a pale grayish-green comet's tail. For the first ten minutes, it was without any fluctuations. The arch died away, but this remained, until at 9.43, it too nearly disappeared, leaving only a trace of its position. Before ten o'clock, it was again bright. At 10.03, the rest of the aurora was dim, and no other streamers appeared. It was now very conspicuous, and remained so until nearly half-past ten, when it finally died away,— a faint haze on the northern horizon alone remaining. All this time, as seen from the position of this streamer back of certain trees and its angle with the horizon, it had maintained precisely the same position with reference to the earth.

Meanwhile, the heavens had revolved past it, the stars first noticed had moved beyond it, and the zodiacal cone had set. The streamer had remained like a great pointer fixed to the earth, marking its motion. While the zodiacal cone gradually sank below the horizon, the auroral streamer had retained its position,— a circumstance well illustrating the cosmical character of the former and the terrestrial character of the latter.