Celestial Photography.-The advance made in this department of science has been so great as to mark an era in astronomical progress. It is now many years since the first successful efforts to obtain by the photographic process exact delineations of the mountains, craters, landscapes, etc., on the moon, and spots and faculæ on the sun, were made; but attempts to photograph the stars, especially those which are telescopic, invariably resulted in failure. Now, however, persistent and long-continued effort united with skill has overcome all obstacles, and success surpassing the most sanguine anticipation has at last been achieved. Stars as faint as the fifteenth magnitude are now depicted on the sensitive plate, giving an absolutely perfect record and a chart of the heavens which in point of accuracy is unapproachable by human hands.

The following is a translation of the report of the Henry brothers, who are connected with the Observatory of Paris, descriptive of the instrument by means of which these wonderful pictures are obtained: "The instrument consists of two object-glasses placed side by side in a hexagonal tube, their optical axes being parallel and separated by a thin partition through its entire length. One of the object-glasses (9 inches aperture and 11 feet focal length) is corrected for visual rays, and serves as a finder. The other (aperture 134 inches and focal length 11 feet 3 inches) is corrected for actinic rays and is used for photography, and covers a field three degrees in diameter." The instrument is mounted equatorially and driven by clock-work, running for three hours without being re-wound, and has very fine independent back movements. The photographic objective is the largest yet made, and was constructed by the brothers Henry.

On the 23d of April last an exposure of one hour gave a fine negative, which on a surface ten inches square, representing five square degrees of the heavens, showed distinctly 2,790 stars from the fifth to the fourteenth magnitudes. Those at the edges of the plate were as sharply defined as those in its center. The stars of the fourteenth magnitude had a diameter of about of an inch. Traces of stars of the fifteenth magnitude can be seen on the negative, but are too feeble to be reproduced on the sensitized paper. By longer exposure not only they but sixteenth-magnitude stars can certainly be obtained. The construction of such a chart made in one hour would, by ordinary methods, require several months of assiduous labor.

The following are the necessary minimum exposures; though, to obtain negatives for good paper prints, triple the time is required:

The table shows that the difference of exposure varies between stars of the first and the sixteenth magnitudes as 1 to 1,000,000. Between two consecutive magnitudes the relation is 2.512. The plates used were the gelatine-bromide. The well-known cluster in Perseus was photographed by these gentlemen in fifty minutes. The negative plate shows stars down to the thirteenth magnitude-509 in all. The telescope employed was a 6.3-inch refractor. After enlarging the photograph four times, it was reproduced by the photo-engraving process, and embodied in the "Annual Report of the Paris Observatory." These copies are on the scale of five inches to a degree.

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Mr. Common, of England, who is authority on this subject, says: Any star that can be seen at all with a telescope can be photographed with the same, and, furthermore, stars that can not be seen at all will, by long exposure, reveal themselves on a negative plate. These facts are on the border-line of the marvelous, and must work a revolution in observational astronomy. Some one has well said, 'A library may now be made, not of books full of figures and descriptions-the accumulated work of many men working many years, each on his own system--but of pictures written on leaves of glass by the stars themselves.""

As there are about 41,000 superficial square degrees in the firmament, and as each negative represents five such degrees, it follows that about 5,000 pictures would include the entire sky, with not one of the 20,000,000 stars, not even those of the fifteenth magnitude, missing.

Eclipses. The regions within which the annular phase of the eclipse of March 16 was visible were mostly upon the ocean and in an uninhabited part of the earth. And, though the eclipse was annular along a line passing through the northern part of California and the Northwestern Territories, yet no extensive arrangements for its observation were made. The scientific interest attaching to an annular eclipse is, however, of little importance compared with that of a total one, for, except for noting the times of the several contacts for the determination of the moon's diameter and of the inequalities of her motions, annular eclipses possess little scientific value. Not so with a total eclipse. For, while his disk is covered by the moon, which sometimes lasts for several minutes, time is had for valuable observations -telescopic, spectroscopic, and polariscopicof the sun's surroundings, especially of the red prominences on the sun's limb, and of the corona which completely and, in certain directions, extensively surrounds him.

The path of totality of the eclipse of the sun on Sept. 8, as is not infrequently the case, was confined almost wholly to the ocean, the only exception being the southern end of the northern and the northern end of the southern of the two islands of New Zealand, where totality lasted nearly two minutes. The last central eclipse visible in these islands occurred on Dec. 29, 1796, and was annular. The next central eclipse in New Zealand will occur on Jan. 3, 1927, and will be annular. During the totality of the solar eclipse of Sept. 8 of this year, the planet Jupiter was within the sun's corona, being but 46' from the sun's linib. In the total solar eclipse of 1870, Saturn had a similar place, being within the corona, yet, strangely enough, appears not to have been seen by any observer. It seems quite logical, therefore, to infer that, if Saturn could thus escape detection, the non-discovery of an intramercurial planet during the total eclipse at Caroline Island need excite no surprise.

Jupiter. The "great red spot" that appeared so unexpectedly and, it is probable, somewhat suddenly in 1878 upon this planet has been made the subject of telescopic study by every astronomer of the world. Many hypotheses possibly all valueless-have been advanced to account for its formation, its color, its drifting both in longitude and latitude, its immense size, and long-continued duration. It is still visible, though so much fainter than during the first two years of its existence as to lead several astronomers erroneously to announce its disappearance. At the present writing it is slowly increasing in brilliance, and its entire outline can now be traced, though it is exceedingly faint, and its color very pale. The extraordinary fact is mentioned by several observersnotably Mr. Denning, of England, and Prof. Young, of Princeton, N. J.-of the appearance of a white cloud upon the red spot and concentric with it, which, being a little smaller, leaves an elliptical annulus of a pinkish hue, about 2" in width, surrounding it. This interior obliteration, now perfect, has been a very gradual process, first remarked about a year ago, but, until March, April, and May last, not sufficiently intensified to attract general notice. At the latest observations of Jupiter, previous to his too near approach to the sun to render further examinations possible, it was thought that the central portion of the spot was slowly filling with matter of a brick-color, but so pale as almost to elude detection. This spot will be watched with increasing interest by astronomers, to ascertain, if possible, if its changes are marked by periodicity. The average size of this spot, which Prof. Hough calls a floating island, is 29,600 miles in length by 8,300 in breadth. Its disjunction with the planet is proved by its drifting in longitude, which during the first year amounted to 10,000 miles, and in the second year to 30,000 miles.

For several years, especially during the past two or three years, there have appeared with

considerable frequency small, round, white spots, with outlines of limb as sharply defined as those of a satellite in transit. The cause of these apparitions lies enshrouded in even deeper mystery than that of those peculiar and interesting markings called his belts, which are never wholly absent, or of the great red spot. In an article on Jupiter's spots by Prof. Young, in the "Sidereal Messenger" for May, 1885, he says: "On March 25 nine brilliant white spots, each as large and several of them as round and as well defined as the disks of satellites, were seen. These bright spots were seen again on April 1, having preserved their configuration sensibly unchanged during the week."

The dark transits of Jupiter's satellites continue to engage the attention of astronomers, but as yet no solution has been reached. No theory of causation, meeting with general acceptance, has been advanced. Many dark transits of his satellites, especially of satellites III and IV, have been observed during the year.

The physical conditions of Jupiter appear, in at least one respect, to be somewhat analogous to those existing on the sun, for, as the sun's rotation period as determined by spots near the equator, gives a different value from that obtained from those nearer the solar poles, so also the rotation period of Jupiter, as ascertained by the rotation of spots near and more distant from his equator, differs, and renders the true determination of this value-though to only a limited extent-a matter of uncertainty. The difference in either case is accounted for by the fact that the spots have a proper motion-that is to say, that they appear disjoined to the bodies themselves and free to move, and seem to drift both in latitude and longitude, particularly in the latter co-ordinate.

To the assiduous labors of Prof. Hough, of the Dearborn Observatory, Chicago, who for several years has made the planet Jupiter a special study, we are indebted for the most accurate value of his rotatory period. The received value for the past hundred years has been:

Comets.-Prof. W. Tempel, of Florence, Italy, while searching for Encke's comet, on the evening of Dec. 13, 1884, ran upon a nebulous object of exceeding faintness, which proved to be the expected comet. Its apparent position was in R. A. 22h 44m 25.63*, Dec. + 3° 44′ 26.3′′. This was its twenty-ninth return to perihelion since its discovery on Jan. 17, 1786, by Mechain. Its period is the shortest of all the periodic comets, being 3.3 years. As heretofore, it exhibited only a short tail (a characteristic of all the known periodics, except Halley's).

Its period is slowly diminishing, having, since 1786, shortened 3 days. No satisfactory explanation of this diminution has been offered. It passed its perihelion on March 7, 1885.

Barnard's comet (I, 1885), the first discovered of the year, was picked up by Prof. Edward E. Barnard, Assistant Astronomer at Vanderbilt University Observatory, Nashville, Tenn., on July 7. It was observed at the Warner Observatory on the 8th, and at Harvard College Observatory on the 9th, at 17-17 31", G. M. T., in R. A. 17 17 48°4", Dec. -6° 1′ 8". It was at discovery a very faint object, and did not subsequently increase in brightness. A short tail, about 2' in length, was on several occasions observed at the Warner Observatory, and perhaps elsewhere. Its prominent feature is its great perihelion distance, equal to 2-516, and greater than that of any recorded comet, with the exception of that of 1729. Its elements present no similarity to any preceding comet; hence, if it has before visited our system, it departed unobserved. If its orbit be a parabola (a fact not ascertained at this writing), it has never previously entered our system, nor will it return again to it, but will remain a wanderer through the stellar worlds, though a denizen of none. The nucleus gave a continuous spectrum over which the usual cometary bands could, with great difficulty because of excessive faintness, be distinguished. The following elements of Barnard's comet have been computed by Prof. H. V. Egbert, of the Dudley Observatory:

Time of perihelion passage, 1885, Aug. 5-2869.
Distance from node to perihelion
Longitude of node...
Inclination...

Perihelion distance..

= 1780 21′ 43′′

= 92° 17′ 27′′

=

S0° 39′ 05′′

= 2.516

Tempel's comet (II, 1867), discovered by Prof. Wilhelm Tempel in 1867, was soon found to have an elliptical orbit with a period of about six years. True to prediction, it returned in 1873, and again in 1879, and in 1885 was again due. M. Raoul Gautier circulated last year a finding ephemeris fixing the date of perihelion passage on Sept. 25, 1884, and of perigee (nearest the earth) on March 31, 1885. The perihelion distance in 1867 was 1,564, the earth's mean distance being taken as unity. These elements show that at perihelion passage in 1885 the distance will have increased by perturbation to 2,073. The nearest approach of the comet to the earth's orbit occurs at or very near perihelion, and it will appear that, under the most favorable conditions of the orbit of 1885, the theoretical intensity of light will not exceed one sixth of the value it might have attained in 1867. At aphelion in the present orbit the comet approaches that of Jupiter.

Armed with Gautier's ephemeris, in April of the present year a most determined effort to find it was made by all the great telescopes of the world, though without success. On April 6, while engaged in a search for it, Dr. Swift, with the sixteen-inch refractor of the Warner

Observatory, found a nebulous object in R. A. 11h 54m 40, Dec. + 20° 3', which, on the evening of the 8th, had disappeared. His description of it was, "Very faint, pretty large, round, and forms a right-angled triangle with two stars." Though the object was doubtless a comet, it differed a little too much in declination to have been Tempel's, unless, since its last appearance, it had been subjected to a greater perturbation in this co-ordinate than computa-. tion had predicted. A diligent though vain search to recover the lost object was made both at the Warner and Cambridge Observatories. The published announcement that the comet had been found in Europe was a mistake. The object seen was one of the many nebula in the region wherein the comet was looked for.

Tuttle's comet (II, 1885), unique in one respect at least, that it belongs neither to the group of short-period comets nor to those of long period, was found in 1790 by Mechain. Its periodicity was not suspected, and it was not again seen until re-discovered by Tuttle at Harvard College Observatory on Jan. 4, 1858. At its next return, in 1871, it was generally observed. It is now visible in the early morning sky, too near twilight to be well seen. It was first picked up at the observatory at Nice, France, on the morning of Aug. 9, 1885, and, two days later, was found at the Warner Observatory, Rochester, N. Y.

The annexed table includes all comets that are known to be periodic. Many others are supposed to be of this class. All of those tabulated have made one or more returns to perihelion since discovery, except Barnard's, Wolf's, and Denning's, but that these are periodics, with elements differing little from those here given them, is unquestioned. Olbers's comet of 1815, expected this year or the next, will increase the number to seventeen, if we include the comet of Biela, which in 1846 was disrupted into two parts. But, as neither fragment has been seen since 1852, it may be considered as irrecoverably lost.

On the evening of August 31, Mr. W. R. Brooks, an amateur astronomer of Phelps, N. Y., and an indefatigable comet-seeker, found a faint nebulous body in the constellation of the Hunting Dogs-Brooks's comet (III, 1885). Its cometary character being strongly suspected, he at once telegraphed his discovery to Dr. Swift, director of the Warner Observatory, which, in compliance with the conditions of the Warner prize, he was obliged to do. As there were five nebulæ in the immediate vicinity of the supposed comet, it was deemed advisable to delay the cabling of the intelligence until confirmation could be had. On the evening of Sept. 2 it was observed at both the Warner and Cambridge Observatories, whereupon Prof. Pickering, director of the latter institution, promptly cabled it to Kiel, Germany, the European center for astronomical telegrams. Thence all important astronomical discoveries are communicated to all the chief ob

=

=

1885. August 16, 1885. September 3, 1885.

No. 244 has been given the name Sita. Of the entire group Athra (No. 132) has the least perihelion distance 1.604, and Andromache (No. 175) the greatest aphelion distance = 4.726, so that their orbits extend over a space of 4.726 — 1.604 = 3.122 of the earth's mean distance, or, in miles, 92,500,000 × 3·122 = 288,785,000 the breadth of the asteroid zone, which, comparatively speaking, nearly covers the region between the perihelion point of Jupiter's orbit and the aphelion of the orbit of Mars. Hilda (No. 153) has the longest period = 7·86 years, and Medusa (No. 149) the shortest 3.11 years.

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Motion of Stars in Line of Sight.—The direction of the displacement of the lines in the spectrum of any heavenly body at once indicates whether it be moving toward or from the earth, and the amount of such displacement marks its velocity. A displacement toward the red end of the spectrum tells with unvarying certainty that the earth and the object are receding from each other, while, on the other hand, if it move toward the violet end, it is indicative of a motion of approach. The rapid rotation of Jupiter on his axis, for instance, causes one limb to approach the observer, while the opposite limb recedes. The diameter

0.9549 0.9675

of the planet and his rotatory period being known, it is easy to compute in miles the velocity with which the two limbs severally approach and recede. These displacements of the lines in direction are used as bases of comparison when observing the changes of the lines in the stars for determination of motion in the line of sight, or, in other words, whether moving toward or from us. This factor is indicated by the spectroscope; the telescope indicates lateral motion only.

For several years Sirius has been the subject of spectroscopic study by several astronomers, notably by Dr. Huggins, who, in 1868, called attention to the fact that the F line in Sirius was displaced toward the red end of the spectrum, and that it was receding from the earth at the rate of about twenty-nine miles a second. A few years later, by the same process, it was ascertained that this rate was diminishing, until, in 1881, its recession equaled only two miles a second, and soon thereafter ceased altogether. Shortly after the cessation of recessive motion, it became apparent that the star was approaching the earth, at first very slowly, but increasing in rapidity until, at the present, it has an approximate motion of about twenty-five miles a second. This singular truth, which, so far as known, is indeed unique, has given rise to a considerable controversy among astronomers. The most reasonable supposition as to its cause is that it is revolving round the center of the system, the star being both a double and a binary, and, as is well known, the brightest star in the heavens-the Dog Star of the Egyptians. The irregularities of the motion of Sirius (not in the line of sight) led to the prediction of a companion star, which, in 1862, was discovered by Alvan G. Clark. It will be of interest to note how these movements in the line of sight will throw light on the orbital motion of its companion. The following table shows the

changes in the direction of motion in the line of sight as determined by spectroscopic observations made at the Royal Observatory, Greenwich, from 1875 to 1885, during opposition, which occurs in the winter months:

Miles.

1875-76.. Sirius moving from us at the rate of 21.1 per sec. 1876-77. Sirius moving from us at the rate of 21 1 per sec. 1877-78.. Sirius moving from us at the rate of 28 0 per sec. 1879-80..Sirius moving from us at the rate of 15.1 per sec. 1880-81 .Sirius moving from us at the rate of 11.8 per sec. 1881-32.. Sirius moving from us at the rate of 21 per sec. 1882-88..Sirius moving toward us at the rate of 4.7 per sec. 1883-34.. Sirius moving toward us at the rate of 19.4 per sec. 1884-'85..Sirius moving toward us at the rate of 21.5 per sec.

At the present time Aldebaran, Capella, and Castor are receding, while Pollux, Sirius, Arcturus, and Alpha Cygni are, at different velocities, approaching our system.

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Dr. Gould announces that the eighth-magnitude star, in R. A. 23h 58m. 1.85", Dec. 37° 58' 18.76" for 1875.0 No. 1584 in hour XXIII of the Cordoba Zone Catalogue, has the very large annual proper motion, in a direction 66° 46' to the east of south, of over 6.2′′ of a great circle. But two stars whose proper motion exceeds the one just described are knownviz., Groombridge 1830, and Lacaille 9352. That of the former amounts to 6.976", and of the latter to 6.9565". The last mentioned, since it was catalogued by Lacaille in 1752, has moved over an arc of 15′ 30′′.

Periodic Changes in the Spectrum of Beta Lyra.Herr von Gothard has contributed to the "Astronomische Nachrichten" an elaborate paper on the changes seen in the spectrum of Beta Lyra during the past year. He secured thirty observations between the middle of February and the middle of November, and found the bands of D, to vary periodically from an almost dazzling brightness to disappearance. As this is a variable star, changing in somewhat less than thirteen days from 5.5 to 6.5 magnitude, it suggests the question whether the sodium lines in all variables do not change periodically, and also whether the period of change coincides with the period of variability.

New Nebula.-This department of practical astronomy has, for many years, been sadly neglected. Lately, however, a fresh interest has been awakened in the minds of a few astronomers possessing large telescopes, and it is to be hoped that ere long the study of the nebulæ may be prosecuted with some of the old-time vigor shown in the labors of the Herschels, D'Arrest, Lassel, Rosse, and Tempel. Only the latter two survive, and they, together with M. Stephan, of Marseilles, France, and Dr. Lewis Swift, of the Warner Observatory, Rochester, N. Y., are the only astronomers now engaged in a systematic search for new nebulæ. M. Stephan has recently contributed to the "Comptes Rendus " a catalogue of one hundred new ones, discovered by himself, reduced to the epoch of 1885 0. This and former catalogues published by him at various times contain about five hundred new nebula. Dr. Swift, since assuming the directorship of the

Warner Observatory, has devoted his entire time to the search for nebula and comets, beginning his quest for the nebula on July 9, 1883. His first catalogue, containing approximate positions of one hundred new nebulæ reduced to the epoch of 1885.0, may be found in the "Astronomische Nachrichten," followed by the publication in the same journal of a second list of a like number.

So thoroughly has the sky been explored by comet-seekers that it may be truthfully averred that, north of 25° south declination, there is not a single undiscovered nebula as bright as Herschel's class I (bright). Of his class II (faint) there may remain a very few. Of his class III (very faint) there are probably several thousands that have escaped detection, which, including those already known, would bring the entire number up to about ten thousand. Since July 8, 1885, forty-six have been discovered at the Warner Observatory. In his first published catalogue, Dr. Swift has included twelve that are the property, by right of original discovery, of his son Edward, a lad of thirteen years.

Dr. Ralph Copeland's stellar nebulæ, like the stars, are mere points, and can only be determined by the spectra they give. During the autumn of 1884 five such objects were discovered by him at Dun Echt Observatory, Scotland, with the star spectroscope after the method of Prof. E. C. Pickering, of Harvard College Observatory, who has also discovered quite a number of the same class of objects.

Occultations.-The only star brighter than a 3 magnitude occulted by the moon during 1885 is Alpha Tauri (Aldebaran), which to some part of the earth disappeared behind the moon thirteen times, or once in each month except September, when it was twice occulted; but three of the thirteen occultations were visible at Washington. Owing to the peculiar position of the moon's nodes, Aldebaran will have been successively occulted 44 times, viz., in 1884 4 times, in 1885 13 times, in 1886 12 times, in 1887 12 times, and in 1888 3 times. To the astronomer, occultations of stars by the moon are of great value, as they enable him to determine with greater accuracy the moon's diameter; to learn of her many inequalities, including the cause and amount of the acceleration of her mean motion, and help him to answer the unsolved problem, How much of this acceleration is due to a gradual decrease in the eccentricity of the earth's orbit, and how much to some other cause or causes? Venus suffered one occultation in 1885, Mercury three, Jupiter three, and Uranus ten, none of which were visible at Washington.

New Star in the Great Nebula in Andromeda.-On September 1 the astronomical world was startled by the telegraphic announcement that on the previous evening Prof. Hartwig, of the Observatory of Dorpat, Russia, had discovered a new star in the center of the great nebula in Andromeda. This is the most conspicuous