passing through the increased thickness. Two years will probably be required for the grinding, polishing, and final testing of this huge lens.

Dr. E. H. Williams, of Philadelphia, has generously given $15,000 for the purchase of a refracting telescope of 16 inches aperture for the observatory of Carleton College, Northfield, Minn. The objective is being made by J. A. Brashear, of Allegheny, Pa., and the equatorial mounting by Warner & Swasey, of Cleveland, Ohio, who two years ago constructed a steel dome for that observatory. This firm has contracts for the construction of two steel domes for the new Naval Observatory, Washington, D. C., one of 45 and the other of 26 feet diameter. The 18-inch telescope and other astronomical instruments formerly belonging to the Chicago Astronomical Society have been removed to the Evanston University, and a new observatory has been built on its grounds at a cost of $75,000, a gift of James B. Hobbs, Esq. Prof. G. W. Hough is director.

The University of Denver has received from the Hon. H. B. Chamberlain, of that city, the gift of an observatory, with generous equipment, costing (buildings and instruments) $50,000. The dome of the observatory is of iron, and is built on the Hough system. The object-glass, 20 inches in diameter and adaptable to photography, is by Alvan Clark's Sons, and its mounting by Fauth & Co. Its director is Herbert A. Howe, Sc. D.

William Smith, of Geneva, N. Y., has built a commodious observatory, and also a dwelling for its director, in the outskirts of that village. The former is furnished with a 10-inch refractor, transit circle, sidereal and mean time clocks, and a Brashear spectroscope. The construction of the steel dome and the mountings of the telescope and transit circle were by Warner & Swasey. William R. Brooks, the discoverer of many comets, is its director.

Many smaller telescopes, which a few years ago would have been considered large, are being constructed in the manufactories of the five principal telescope makers of the world, viz., the Clarks, Brashear, Grubb, Calver, and Cook.

Telescopes for Photography.-Prof. Barnard, of Lick Observatory, in a letter to the Royal Astronomical Society, published in the March number of the "Notices," says: "The photographic telescopes now being made, except the Bruce telescope, will give us but little information about the structure of the Milky Way, as the field of view will be too small to show the cloud forms. What is wanted is a photographic chart of the Milky Way made with a short-focus portrait lens of the largest attainable aperture-one that will cover at least 100 square degrees." The writer has received from him two photographs of the great nebula in Andromeda and two of the Milky Way, the former showing 64,000 stars, the latter stars innumerable, and its cloud forms perfectly and beautifully delineated, the work of a camera bearing a 6-inch objective. These cloud forms are wonderfully true to nature, and this is the first time they have been truly revealed by photography or by any other method.

Comets. Since the last report the following named comets have been discovered: Comet ƒ 1889 was detected at Warner Observatory, Roch

ester, N. Y., by Dr. Lewis Swift, on Nov. 16. From its small inclination, it was immediately suspected to be a periodic-a fact confirmed by computation from subsequent observations. The subjoined elliptic elements, computed by Karl Zelber, differ but little from those made by others: Time of perihelion passage, Nov. 29-66411 Berlin mean time; longitude of perihelion, 40° 55′ 52.8"; longitude of node, 331° 26′ 40-1"; inclination, 10° 3' 21.1"; perihelion distance, 1.19; period, 6.91 years.

It is probably the faintest of all the periodic comets, D'Arrest's not excepted.

Comet g 1889 was discovered by M. Borelly at Marseilles, France, on Dec. 12. Though it was faint at discovery, its brightness increased to 23:52 on Jan. 24, 1890, or to more than twentythree and a half times its brilliancy at discovery. Its motion was rapidly south, and it was soon lost to view from northern observatories. The following elements were computed by A. Berberich: Time of perihelion passage, 1890, Jan. 26.5143 Berlin mean time; node to perihelion, 200° 1.52'; longitude of node, 8° 17-82'; inclination, 56° 43-43'; perihelion distance, 0.26926.

Comet a 1890 was found by Prof. W. R. Brooks, Director of Smith Observatory, Geneva, N. Y., on March 19. It was faint when discovered, but in June had attained a brightness five and a half times that of March 19. At this writing (Oct. 1) its brightness =0.55, and it is running well with the ephemeris computed from the following elements by Prof. O. Ĉ. Wendell, of Harvard College Observatory: Time, 1890, June 1.15896, Greenwich mean time; longitude of perihelion, 29° 2' 15.5"; from node to perihelion, 320° 18′ 55'6"; inclination, 120° 30′ 56′5′′; perihelion distance, 1.9091.

Comet b 1890 was discovered, on July 19, by M. Coggia, of Marseilles Observatory, France. Though telescopic, it must have been rather bright at its perihelion passage, as it was of fair brilliancy at discovery, but grew fainter so rapidly that in twenty days it had diminished one half. The elements of its orbit, as computed by F. Bidschof, are: Perihelion passage, 1890, July 8.730, Berlin mean time; from node to perihelion, 85° 58.5'; longitude of node, 14° 25'6'; inclination, 63° 14'6'; perihelion distance, 0·7661.

Comet c 1890 owes its discovery to William F. Denning, of Bristol, England, on July 23. It was both faint and small, with motion almost exactly south. Gradually increasing in brightness, it reached 2.21 on Sept. 2. These are its elements, according to Berberich: Time of perihelion passage, 1890, Sept. 24-6489, Berlin mean time; from node to perihelion, 161° 22′ 24·9′′; longitude of node, 98° 47′ 39′7′′; inclination, 99° 13' 38-7; perihelion distance, 1.2838.

Comet d 1890 was discovered on Oct. 6 by Barnard in right ascension 19h 13m 30, declination 26° 7' 30". Subsequent observations proved it to be D'Arrest's periodic comet, which astronomers for several months had been searching for.

Denning's periodic comet of 1881, which was expected to return to perihelion during the early months of 1890, was not found. Search for it was almost useless, as the geocentric positions of both the comet and the sun were so nearly alike that when near enough to have been other

wise visible the comet was constantly immersed in the sun's rays. No doubt is felt about its periodicity, though it has been observed at only one return. At its next appearance, in 1899, it will be better placed for observation.

The following periodic comets were expected at perihelia in 1890, but up to Oct. 1 not one of the three has been found: Barnard's 1884 II, Brorsen's of 1846, and Coggia's of 1873. The elements of the first of these strongly resemble those of De Vico's comet of 1844 I, and also those of Finlay's comet 1886 VII. Brorsen's was diligently sought by many astronomers with large telescopes, but without success. It was seen in 1846, 1857, 1868, 1873, and 1879, but eluded observation in 1851, 1862, 1884, and 1889. At its recent return it was well situated for observation. Coggia's, which is supposed to be identical with Pons's comet of Feb. 23, 1818, was not searched for. It has not been seen since 1873, though a period of five and a half years has been assigned to it.

Barnard's comet e 1888 = Comet I 1889, is at this writing still visible as an exceedingly faint and small object, even with the Lick glass of a yard in diameter. It was first found on Sept. 2, 1888, and has, therefore, a visibility of more than two years' duration, the longest of any comet on record.

Identity of Periodic Comets.-In the "Astronomische Nachrichten," No. 2,964, M. Schulhof, of Paris, has an instructive paper entitled "Notes on Some Comets of Short Period." It discusses the probable identity of several pairs of periodic comets of short period, and also the possible identity of several, as Finlay 1886 VII and De Vico 1884, Denning 1881 V and Pigott 1783, Blanpain 1819 and Grischaw 1743 I, Coggia 1873 VII and Pons 1818 I, and others. Prof. Seth C. Chandler, in "Gould's Astronomical Journal," Nos. 204 and 205, has proved to the satisfaction of a majority of astronomers that Comet V, 1889 (Brooks) is identical with the long-lost Lexell comet of 1770; but M. Schulhof regards as more probable the identity of the Lexell comet with Comet 1886 VII (Finlay's). When it is remembered that the orbit of Lexell's comet, by its near approach to Jupiter in 1767, was changed from a parabola to an ellipse with a short perihelion distance, thus rendering it visible, and that in 1770 it was again perturbed and made invisible by a still closer approach to that planet, which caused an increase of perihelion distance, and, also, that Jupiter has several times exerted his powerful attraction in changing its orbit, the question rises whether there are none among the large number of known comets of short period identical with this lost one.

It is highly improbable that of all the short-period comets, or even a tithe of them, are or ever will be known to astronomers. The facts of the division of Biela's comet into two perfectly formed comets which for at least six and a half years maintained their cometary character and individuality, the separation of the great comet of 1882, the recent division and subdivision of Brooks's comet of 1889, and, furthermore, the remembrance that this process has been going on since the solar system has existed, filling it with subdivided comets too faint to be detected by any known optical means, carry us into a

realm of the wildest speculation as to the number of these bodies in the solar system.

Synchronical Revolution and Rotation of the Planet Mercury.-Signor Schiaparelli, of Milan Observatory, Italy, has given astronomers a surprise somewhat akin to the discovery of Neptune and of the satellites of Mars. He announces, as the result of a discussion of one hundred and fifty drawings of Mercury, covering seven years of observation, that that planet completes but one rotation during a revolution around the sun, exactly as the moon rotates on her axis once while she revolves round the earth. He arrives at the conclusion that Mercury completes a rotation on its axis in 87,969 days, which is the exact time of his period of revolution around the sun. If his deductions be true, it follows that one Mercurial hemisphere is constantly bathed in sunlight, while the other is enveloped in perpetual darkness. Observations of this planet are always unreliable and unsatisfactory and must always be made under difficulties, because he is ever in direct sunlight or in strong twilight (in the latter case at a low altitude), and hence the conclusions of this distinguished astronomer require strong confirmation from other observers. Were his assumption true, it does not follow that an exact half of the planet is forever devoid of sunlight, as, owing to his small size compared with that of the sun and also to his nearness to that luminary, there will be exposed to his direct beams in excess of one half of his surface a belt nearly twenty miles in width entirely around the planet, whose breadth must be still further increased by refraction from an undoubtedly existing atmosphere, and (because of the great eccentricity of his orbit) by greatly extended librations, and from these, and perhaps other causes, it may be that not much over one fourth of the planet is in unending darkness. The same astronomer claims to possess evidence to warrant the declaration that Venus also rotates on her axis but once during a revolution around the sun, or in 224-7 days.

Oxygen in the Sun.-Since the invention of the spectroscope, the presence of oxygen in the sun has been denied by many spectroscopists, while others have testified to having obtained unmistakable evidences of it. By a series of observations of the spectrum of an electric light placed on the Eiffel Tower in Paris, as examined from his observatory at Meudon, M. Jansen has confirmed the conclusion he drew from his observations made in 1888, that the supposed oxygen lines in the solar spectrum are due wholly to the influence of our own atmosphere. This, if true, is of great importance; for while more than half of the earth and its atmosphere consists of oxygen, it is indeed remarkable that this should be entirely absent from the sun in which twenty or more other telluric elements exist, as proved by spectrum analysis. Its absence from that body affords a strong argument against the theory of the earth's having originally been evolved from the sun.

Sun-Spots. In 1889 the sun was free from spots for 211 days, the longest spotless period being from Oct. 23 to Dec. 11. There were also eight others of more than two weeks' duration. The mean daily area, however, for the latter half of the year was nearly twice as great as for the

No. 282 has been named Clorinde; 286, Iclea; 287, Nephthys; and 288, Glauke.

Mars. At the opposition of Mars in 1890 his altitude was so low for northern observation as to render abortive every effort to improve our knowledge of this planet. In another respect it was also unfavorable, viz., the earth's aphelion and Mars's perihelion were not coincident with his opposition. The duplication of his canals, put forward so confidently by their alleged discoverer, Schiaparelli, was not visible with the 36inch refractor of Lick Observatory, nor with other large telescopes, and their existence is not generally credited among astronomers. At Mount Wilson, where the great observatory for the 40inch lens is to be erected, seven photographs of the planet were taken on April 9 between 22 56m and 23h 41m Greenwich mean time; and seven more on April 10, between 23h 20m and 23h 32m, the same face of the planet being presented to the earth in both cases. Distinct and identifiable spots and markings are shown in all the fourteen pictures, but on those of the latter date a considerable accession to the white spot surrounding the south pole is shown. It is, says Prof. W. H. Pickering, in Payne's "Sidereal Messenger" for June, 1890, surprisingly large, amounting to about 25,000,000 square miles. He makes no mention of the duplication of the planet's canals having been seen on any of the plates.

Saturn.-The unique observation of an eclipse of the satellite Japetus by the shadows of the globe, the crape ring, and the bright ring of Saturn was made with the 12-inch telescope of Lick Observatory by Barnard on Nov. 1, 1889. The phenomenon was expected, and he was prepared for the work, with, fortunately, a clear sky. The satellite was first seen to emerge from the shadow of the globe, pass into the semi-shadow of the crape ring, and finally disappear in the shadow of the inner bright ring, when approaching daylight prevented further observation. The diminution of brightness of the satellite while in the shadow of the crape or gauze ring was easily apparent, and confirmed the latter's translucency, which fact has long been received. But the shadow of the bright ring was as dense as any opaque body could cast, as much so, indeed, as was that of the planet itself, and this tends to disprove the theory that it is made up of an infinite number of satellites. And the fact that

both edges of both the bright rings are as clean cut and as sharply defined as the limb of the planet is another argument against the satellite hypothesis. Mr. Lockyer claims to have obtained some photographic evidence of the existence of bright lines in the spectrum of Saturn, but Dr. Huggins saw no lines save those given by ordinary sunlight.

Jupiter and his Satellites.-The great red spot, floating, probably, in the atmosphere of Jupiter, which for a dozen years has been under observation, is still visible, though from the planet's low altitude at this year's opposition, it is an extremely difficult object even with the largest telescopes. Spots of several varietiespale-red, white, and black-appear on his disk. Recently a black one has made its appearance on his southern equatorial belt, which, like the "great red spot," has a motion of translation in such direction and at such rate that one has occulted the other. A. Stanley Williams, who has directed attention to this interesting phenomenon, calculates that the black spot, if it remains visible and progresses uniformly, will be in conjunction with the following (east) end of the red spot on July 29, with the center on Aug. 28, and with the preceding (west) end on Sept. 27, thus requiring two months to pass over or under the red spot.

Two of his satellites-the third occasionally, the fourth very rarely-traverse Jupiter's disk as black objects. A striking instance, observed at the Warner Observatory, occurred on the evening of July 21, 1890, when the third satellite and its shadow were both on his disk simultaneously, the satellite being, if possible, more densely black than its shadow. It usually traverses as an object with brightness so nearly equal that of the planet as to be hardly discernible. No satisfactory explanation of this phenomenon has been given, as the sun shines alike on both disks, and, if the reflective powers of both planet and satellite are the same, as they generally seem to be, the satellite while on the planet's disk ought not to be visible except when superimposed on one of his belts.

Zodiacal Light.-In No. 2,976 of the "Astronomische Nachrichten," Prof. Arthur Searle, of Harvard College Observatory, has a paper on this theme, it being a summary of what is to appear in extenso in Vol. XIX, Part II, of the "Annals" of the observatory. It contains the records of this phenomenon for the past fifty years. The three main topics to which attention is called are: 1, the permanence of the ordinary western zodiacal light; 2, the normal distribution of light in the Zodiac and its vicinity, which evidently affects all observations of the fainter portions at greater elongation; 3, the phenomenon of a feeble maximum of light in opposition to the sun, commonly known as the Gegenschein. A daily record kept since 1877 shows that the zodiacal light must be considered as a permanent phenomenon, subject to only slight variations apart from atmospheric causes. This concurs with the writer's conclusions, resulting from many years of observation, that the oft-repeated statement of wavy motion seen in the zodiacal light is without foundation. The same applies also to the flickering motion, similar to the merry dancers" in the Aurora Borealis, imag

ined in the tails of comets. Prof. Searle inclines to the belief that the light is sometimes variable, but asserts that the delicacy of the work requires independent observation by different astronomers made simultaneously, under like atmospheric conditions, and kept up for several years. Of the Gegenschein, of which a comparatively large number of observations have been obtained, he says, "All are confessedly uncertain." Though the writer has never seen the Gegenschein at the Warner Observatory, yet he enjoyed at the Lick, in January, 1889, several unmistakable views of it. It appeared as a circular luminous patch of extreme faintness, about 5° or 6° in diameter, exactly opposite the sun, having a daily progressive motion equal to the sun's apparent motion in the ecliptic.

The Sun's Motion.-"Gould's Astronomical Journal" has an instructive paper by Prof. Lewis Boss, Director of Dudley Observatory, Albany, N. Y., on the proper motions of 295 stars and his conclusions therefrom regarding the direction of the sun's motion in space. Of all this number of stars, only 49 have been previously used by others in a similar investigation, and, therefore, his determinations are independent of the results obtained by others. The stars were divided into two groups according to magnitude, the mean magnitude of the first group 6-6, and of the second 86. He found the mean maximum motion of the sun, as viewed from the mean distance of both groups of stars, to be 13-06" in one hundred years toward a point nearly 5° north of west of Alpha Lyra, right ascension 280°, declination + 40°. Sir William Herschel's point was 260° 34′ + 26° 17'. The mean place of four determinations by Argelander, Luhndahl, Struve, and Galloway is right ascension 258 + 28° 7'. These results are not in very near accord, yet, considering the intricate nature of the problem, the agreement is, perhaps, as close as could be expected. It is undoubtedly true that the apparent motion of these stars is partly due to a relative motion of our sun, and, of course, of the entire solar system toward the point named, at the rate of 10 or 15 miles a second; but whether this latter movement is curvilinear or rectilinear, posterity, ages hence, must determine.

Orbits of Binary Stars.-Mr. Gore, of England, has recently published an orbit of Sirius, and finds a period of 58.5 years, and that, with Guylden's parallax (=0·193'), the sum of the masses of the star and its companion is 26-25 times that of our sun, and the mean distance of the components from each other 445 times that of the earth from the sun, or about one and a half times the solar distance of the planet Neptune. The same astronomer announces that, from recent measures, the binary star Struve 228, has described about 120° of its apparent orbit since its discovery in 1829. A computation of its orbit gives a period of 88-73 years, and its time of peri-astral passage as A. D. 1906. Its present distance is almost exactly one second, but at peri-astron the components will probably be separated by less than 0-2". It is a very interesting binary, which in a few years but few telescopes will be able to divide. Its position is right ascension 2h 6m 59a, declination + 46° 58'4'. The magnitudes of the components are 67 and

76. He also has deduced the provisional elements of the orbit of Delta Cygni, and makes its period 376-659 years, its peri-astral passage A. D. 1914, and its present distance 2:39". For the binary Gamma Corona Australis, E. B. Powell has calculated an orbit, and finds a period of 93-338 years; peri-astral passage A. D. 1885, 122; distance, 2034", with an annual retrograde motion 3° 51′ 25′′.

Astro Photography. A beautiful photograph of Jupiter was taken on July 12, 1890, by Prof. W. H. Pickering at his temporary mountain observatory on Wilson's Peak, California. Its scale is 00000000, or 1.65"=1 millimetre magnified (at 29 c.m. distance) 450 times. The 13-inch telescope was used. The exposure, only 87 seconds long, shows his system of belts with surprising distinctness. At the same place, on Feb. 7, 1890, the planet Saturn was exposed for 6m 16, scale 30000000 or 0.84" 1 millimetre magnified 770 times. Both bright rings and the division between them, also the dark ring and the equatorial belts, are plainly visible. A remarkable photograph of what he calls "an inky black hole in the Milky Way (coal sack) has been made by Prof. Barnard at Lick Observatory. This study is in Sagittarius right ascension 17h 56m, declination south 28°. Much of its inky blackness is undoubtedly due to contrast with its surroundings, which are very bright from the mingled light of many thousands of telescopic stars. The 16-inch objective of the Warner Observatory shows but five stars in it, four of these needing closest scrutiny, yet the photograph shows myriads of stars, very few of which are visible in the great 36-inch telescope. The exposure was continued for 3h 7m. The instrument employed was not a telescope, but a portrait camera, the lens having an aperture of 5.9 inches. It was mounted temporarily on a rough wooden box and strapped to the tube of the 6-inch equatorial telescope, which latter was used simply as a pointer. Though driven by clock-work, it was necessary to keep it exactly directed on a star by slow-motion hand-rolls, one moving it when so required in right ascension, the other in declination. These vacuities are thickly interspersed along the Milky Way, and Barnard's system of photography will probably reveal countless stars in them all. In observing this hole or cavity Sir William Herschel proclaimed that he had sounded the depths of the Milky Way with his great telescope, and had penetrated to the dark, starless regions beyond.

W. E. Wilson, of Ireland, has invented a method of recording transits by photography, whereby personal errors are eliminated. A sensitized plate is placed in the focus of a transit instrument, and if a star traverse it uninterruptedly, a continuous black line will be found on the development of the plate, thus but if an up-and-down motion be given it by the electric clock, the result is a broken line of this -, each break being equal to a sidereal second. With only a rough apparatus the inventor found the recorded time of transit correct to within one fourth of a second.

sort

Andromeda Nebula.-Isaac Roberts has published in "Himmel und Erde," and reproduced in the "Sidereal Messenger" for January, 1890, a magnificent photograph of the nebula in An

only photographically. The nebula proper, the rings, the spaces between, and its surroundings are dotted with thousands of stars, as the engraving clearly shows, though, it must be remembered, it is designed to show details of the nebula itself rather than the stars in its neighborhood, which would have required a much more prolonged exposure. Prof. Barnard has also successfully photographed this nebula, or rather its surroundings, as the over-exposure (4h 18m) to attain

We have recently considerably extended the nebulosity about Theta by giving longer exposures and using a quicker lens. The connection with c is now well marked, while the long nebulous streak extending southward from Zeta is broadened and joins c upon the other side, connecting the sword-handle with the belt. This extension is of much greater area than the other two. nebulæ combined. Its northern portion as far as 3° 30' south declension is fairly conspicuous, and makes an excellent test object, not of the instrument or the steadiness, but of the clearness of the air and the blackness of the sky. Owing to recent advances in stellar photography, this matter of sky illumination has assumed considerable importance, and it is very doubtful if any of the fainter nebulous extensions here described can be photographed at any observatory located in or near a large city. This is due, undoubtedly in part to the gas, but chiefly to the electric lights which illuminate the slight atmospheric haze and aqueous vapor. A large spiral nebula, which starts from between Omega and Psi, is seen on the plate, passing four degrees north of Zeta, extending to Beta, thence north to Eta, with an outside stream lying nearly north and south, and preceding Beta about four degrees. Another stream, lying nearly east and west, precedes Eta about the same amount. This nebula is about 15° in length by nearly the same breadth, and surrounds a cluster of bright stars,