and that no exact limit can be set to it; but he has extended it to about twice the wave-length previously known, and believes that beyond this the heat can scarcely pass through the atmosphere at all, and therefore is nearly all absorbed before it can reach any human eye. Dr. Frolich, of Berlin, bas devised apparatus for the purpose of comparing the solar heat from day to day with that radiated from a box which was blackened with smoke and kept filled with steam. His regular measures were taken in and near Berlin, but he also made observations on the Faulhorn at the height of 9,000 feet. From his data Dr. Frolich found that the solar heat diminished when the spots were more numerous, while the higher gradations of heat were attended with fewer sunspots. This result, although suspected by other observers, has not, however, been proved. The Maximum of Solar Spots.-The last epoch of greatest sun-spots which has been investigated occurred, according to Dr. Wolf, about the end of the year 1870. From previous observed maxima Dr. Wolf fixed the period at 11.1 years; this would bring the next computed maximum at the beginning of 1882. It appears, however, that this maximum has been delayed by one or even two years, as it was not until after the middle of 1884 that the diminution of the spots was so well marked as to show that the maximum had actually passed. It is noticeable that this epoch has not been marked by auroral displays of such brilliancy as have sometimes been observed. The maximum of 1860 was most remarkable in this respect. It has sometimes been supposed that brilliant auroras appear at every third sun-spot maximum; if such is the case, the year 1894 may be expected to be one of brilliant auroras. Solar Parallax and Velocity of Light.-No important additions have been made to published discussions on the subject of the solar parallax; but determinations of the velocity of light and the constant of aberration have been made which promise to give a more accurate value of the important constant than any that can be made by direct measurement. The new determinations of the velocity of light, made first by Prof. A. A. Michelson, and then by Prof. S. Newcomb, agree in giving a velocity of light not far from 299,860 kilometres per second. The three separate results are: NAME. Michelson Michelson Newcomb result with the above velocity of light gives 8.794" as the solar parallax, a result in good agreement with the best recent measures. The corresponding distance of the sun may be stated in round numbers as 93,000,000 miles, which we are now entitled to regard as the most probable result, and which is not likely to be altered by much more than 100,000 miles by any future discoveries. The fluctuations in the adopted value of this distance have been very remarkable. From 1825 to 1855 the distance 95,000,000 miles, found by Encke, was received with a degree of confidence entirely unwarranted by the character of the observations on which it depended. When it was found to be in error by a larger amount than was expected, it was rejected without due examination, and from various observations made about 1860 the distance was supposed to be about 91,000,000. Subsequent investigations have shown that these two extremes were almost equally far from the truth, and every important step since taken has been in the direction of the old value. Reduction of the Transit of Venus Observations of 1882.-Although the observations of the last transit of Venus succeeded much better than those of 1874, no definite information is yet available respecting the progress of the reductions in foreign countries. In the United States the work of the commission has been directed principally to the measurement of the photographs and an examination of the instruments with which the photographs were taken. The measurements of the photographic plates have been completed under the direction of Prof. W. Harkness, U. S. N., and a careful investigation of the action of the photo-heliograph under the influence of the sun's ray is now in progress. It is found that the reflectors change their figure under the influence of the sun's rays by an amount which is very appreciable when the most delicate measures are employed. The following table shows the various stations at which photographs were taken according to the plan devised by the American commission, and the number which are available at each: The agreement of these results shows them to be sufficiently near the truth for the determination of the parallax. The more difficult and uncertain question is that of the exact time required for light to pass from the sun to the earth. A new determination of the constant of aberration, which depends upon this time, has been made by Nyrén, of Pulkowa, giving the result 20"-492. The combination of this VOL. XXIV.-4 A At Auckland, New Zealand. they would be entirely invisible except when Mars was near perihelion. They have, however, been well observed at every opposition since their discovery, including that of 1884. It is now expected that in the most powerful telescopes they will be visible even in the least favorable oppositions, including those of 1886 and 1888. The Planet Jupiter.-It has for some time been suspected that the planet Jupiter bore a remarkable resemblance to the sun, in that its equatorial regions rotated in less time than those nearer the poles. This view seems to have been entirely confirmed by observations upon the remarkable red spot which was visible from 1879 until 1883. This spot was in the middle latitude, and from its motion the following periods of rotation of the planet on its axis were obtained by Denning, of England: By comparing the observations of Sir William Herschel in 1789, one by Sir John Herschel at the Cape of Good Hope in 1837, and his own observations, Prof. Hall found the sidereal revolution to be performed in 79-3310152 days. From these results, the mass of Saturn comes out of that of the sun. This mass is one half per cent. greater than that of Bessel, and more than one per cent. greater than that found by Leverrier. It agrees, however, with other determinations from the motions of the satellites, and especially with the conclusion of Dr. Meyer described in the "Annual Cyclopædia" for 1883. The other researches refer to the motion of Hyperion, the minute satellite discovered by Bond in 1848, the orbit of which is next within that of Titan. Some years ago Prof. Hall showed that the line of apsides of the orbit of this satellite was revolving in a retrograde direction. This was apparently in contradiction to the received results of gravitation, since the secular variation should be from west to east. But in a paper published by the Royal Astronomical Society in May last, it was shown by the comparison of all the observations since 1852 that there could be no doubt of this seem From a white spot near the equator the fol- ingly anomalous motion. This unexpected relowing times of rotation were obtained: It thus appears that there is a difference of more than five minutes between the period of rotation at the equator and in the latitude of the spot. This result is of great inter est, as showing how great the analogy is between the planet Jupiter and the sun. No satisfactory explanation of this more rapid rotation at the equator has yet been found. Since the distance which the equatorial regions of the planet must travel in order to make one complete revolution is greater at the equator than anywhere else, the time of its revolution should, it might be supposed, be greater, instead of less, as we actually find it. Saturn and its Satellites.-Important and interesting researches on the Saturnian system have been made by Prof. Asaph Hall with the great Washington telescope. One of these researches has led to a more certain value of the mass of Saturn than any before attained. The mean distance of the outer satellite was found from the observations of 1875, 1876, and 1877, which give the following separate values of this element, when seen from a point distant 9.53885 astronomical units: 1875;515-594" ± 0·056". 1876; = 515-454” ± 0·058", 1877;= 515-517′′ ± 0·058′′. Mean; = 515-522′′/ 57 observations. 40 81 66 sult led Prof. Newcomb to investigate the subject, and he found that the motion was due to the fact that three times the period of revolution of Hyperion was very nearly equal to four times that of Titan, the largest of the satellites, which lay next within the orbit of Hyperion. The correspondence was not perfectly exact, and the result of its not being exact was that the line of apsides was dragged around as it were by Titan, in such a way that all conjunctions of the two satellites take place at or near the point when Hyperion was farthest from Saturn. Thus there exists a third case of a relation among motions in the solar system. Those previously known were the rotation of the moon on its axis, which we know to correspond exactly to its time of revolution around the earth, so that the same face is always presented to us, and the relation among three of the satellites of Jupiter which prevents their ever being in conjunction at the same time. In the spring of 1885 the ring of Saturn reaches its greatest inclination to the line of sight of an observer on the earth. The winters of 1884, 1885, and 1886 are, therefore, the the most favorable for studying the planet and its rings which astronomers will enjoy until another revolution is completed, which will not be until 1914. It is understood that, under favorable circumstances, Prof. Hall has succeeded in seeing the planet through the division in the ring, thus showing beyond doubt that the division is a real gap, and not merely a dark portion of the ring. So far as known, the observations made with the great Washington telescope do not confirm the view which has sometimes been expressed by astronomers, that the rings of Saturn change their aspect from time to time. Observers have sometimes described the outer ring as broken up into a number of concentric rings, thus giving rise to the theory that this ring was sometimes continuous, and sometimes divided up. A somewhat ill-defined shaded line, known as the Encke division, is always seen under favorable circumstances near the outer edge of the outer ring, and this appearance may have given rise to the impression of one or more divisions. Nor has any separation ever been seen between the dusky ring and the inner edge of the bright ring. In fact, the latter seems to fade into the former by insensible gradations of shade. On the other hand, Mr. Trouvelot, who was formerly attached to the Harvard College Observatory, but who has returned to Meudon, France, expresses himself very decidedly in favor of the supposed changes. These changes he claims to consist 1. In variations of the brilliancy and color of the surface of the rings. 2. In changes, sometimes slow and sometimes quite rapid, in the form of the shadow cast by the globe of the planet upon the rings. 3. In variations which affect the ring throughout its entire thickness. At the last opposition he found that the Encke division had entirely disappeared, and that its place was taken by a new division, more marked and nearer to the old and well-known one of Cassini. He also noticed that the narrow belt between this new division and the old one was more brilliant than he had ever before seen it, and was subject to fluctuations. The question of variability must still be an open one which can be decided only by comparing simultaneous observations made by observers at distant stations. Until this is done it will be safest to attribute the supposed changes to variations in the state of the atmosphere and the eye of the observer. The physical features of the ball of the planet have been investigated by a number of English investigators. At the January meeting of the Royal Astronomical Society, Mr. Green said that the outline of the ball could be traced on either side for some little distance through the dusky ring. This coincides with the observations made some years ago by Mr. Trouvelot with the great Washington telescope, and, if correct, show conclusively that the dusky ring is transparent, at least near its inner edge. The studies made by Mr. Green and Mr. Pratt indicate a remark able resemblance between the balls and other markings on Saturn and those on Jupiter, the principal difference being that the former are very much fainter, and can therefore be made ont only under favorable conditions. Around the equatorial region extends a zone of a creamy yellow tint, which is usually free from markings. At about latitude 10° there is a strongly marked narrow belt, sometimes gathered into wispy notches and curved markings, as on Jupi ter. The color of this belt is a Vandyke brown. Several alternate belts, ranging from a creamy tint to a very pale rose madder, are seen in middle latitudes, and terminate with the bluishwhite polar cap. The Zone of Asteroids.-The discoveries of small planets, which fell off so remarkably during the years 1882 and 1883, were recommenced with their old vigor in 1884, nine being discovered during the latter year. This carries the whole number now known up to 244. The following table shows the discoveries of the year: Cometary Discoveries in 1884.-The first comet discovered in 1884 is catalogued properly with the comets of the preceding year, as it passed perihelion on Dec. 25, 1883. It was discovered by Ross, an amateur observer at Esternwick, near Melbourne, Australia, on Jan. 7, 1884, a "faint nebulous object with an ill-defined, taillike projection." By January 18th, the tail had reached a length of a degree and a half. The comet was invisible in the northern hemisphere, and was under observation at the southern observatories for only about a month. The first comet of 1884, in order of peribelion passage, was that discovered by Brooks at Phelps, N. Y., on Sept. 1, 1883 (comet C, 1883). As soon as sufficient observations were obtained to determine approximately the orbit, it became evident that this was a return of the comet originally discovered by Pons at Marseilles on July 20, 1812, one of a group of which Halley's comet is another member, having a period of about seventy-five years, and an aphelion a little beyond the orbit of Neptune. As the second comet of this group to return to perihelion, the comet was looked for with considerable interest, and this interest was subsequently increased when observations showed the rapid changes suffered by the head in approaching the sun, and the curious fluctuations in the brightness of the nucleus. From a star of the eleventh or twelfth magnitude at the time of discovery, it increased gradually in brightness to the 7 magnitude on September 23, and then suddenly decreased to the ninth magnitude on September 29. A gradual increase again took place till October 6, when it was a second time noted as 7 magnitude, and then, after another short period of decrease, a final steady increase in brightness began abont the first of November, and continued until a maximum of the second magnitude was reached, about the time of perihelion, in the latter part of January. From Nov. 27, 1883, to March 3, 1884, the comet was reported visible to the naked eye. The tail, which was detected about the first of December, attained a length of six by January 20, and then faded out gradually until it was invisible even in the telescope by February 26. The nucleus was observed as late as March 29, 1884. The spectroscope gave the usual hydrocarbon spectrum of comets. till June 17 and 18, and then the object could no longer be seen; nor could it be found afterward. It is still doubtful whether this was the expected comet of 1858 or not. Pickering's Photometric Researches.-The application of the photometer to astronomical research has been a specialty of the Harvard Observatory since Prof. Pickering became its director. The method of observing the eclipses of Jupiter's satellites by the photometer is likely to be a great improvement in The second comet of 1884, in order of peri- accuracy upon the older eye-methods, and may helion passage as well as of discovery, was be expected to supersede them for all the purfound by Barnard, at Nashville, Tenn., July 16, poses of accurate astronomy. The greatest 1884. It was a nebulous object, slightly con- work of this class is the determination of the densed near the center, and, for a telescopic brilliancy of all the stars down to the sixth comet, quite bright. The orbit proved to be magnitude visible at Cambridge by means of elliptical, with a period of about 5 years, peri- a meridian photometer. The latter is an inhelion occurring August 16. The elements strument of Prof. Pickering's invention. It is bear a remarkably close resemblance to those so arranged that an image of the pole-star is of De Vico's comet of 1844 (1844 I), but the always visible in the field of view, and is used identity of the two objects is improbable. The as a standard of comparison. The instrument comet, at no time prominent, was last reported itself is mounted in an east-and-west horizontal visible about the end of October. position. It has two objectives of the same aperture and focal length. A prism in front of each reflects the light of a star, the one being used for the pole-star, and the other for the star to be measured. The latter prism may be turned round the axis of the telescope, so as to form an image of any star sufficiently near the meridian. The two pencils as they leave the object-glass are each divided by a double refracting prism, in such a way that one ray from each is made to coincide. The result of many ingenious devices and precautions is, that the images of the two stars can be brought into close juxtaposition, and by means of a polarizing apparatus the two images can be brought into exactly equal brilliancy. The observations occupied the four years, 1879 to 1882, and the results, as published in Volume XVI of the “Harvard Öbservatory Annals," form one of the most available catalogues of the brightness of stars now at the command of astronomers. A new comet was discovered by Wolf, a student of astronomy at Heidelberg, on Sept. 17, 1884. It appears to belong to the group of the Faye-Moller comet (comet 1857 IV, and comet 1874 IV). There is no evidence of any previous appearance, though, if the period of 6.75 years assigned is correct, it would be visible from the earth at only about every third return. The comet shows a pretty welldefined, star-like nucleus surrounded by its nebulous envelope, but it has not developed a tail. Perihelion was passed Nov. 17, 1884. The fact that this comet was never before observed, although it is now moving in an orbit in which the time of revolution is less than seven years, led Dr. Krueger to investigate the question whether we had not another case of a comet taking a new orbit by the action of Jupiter. Tracing back the course of the comet, he found that about May 28, 1875, it must have passed very near to Jupiter, and might therefore have had its orbit entirely changed. Another astronomer has undertaken to compute the change produced in the orbit by this approach, and found that before 1875 it might have been moving in a much larger orbit. This result is, however, entirely uncertain, owing to the want of exact knowledge of the time of revolution. All that can be said with confidence is that a great change was produced by the action of Jupiter. It will probably perform seven or nine revolutions in its present orbit without again approaching Jupiter, and may then again encounter that planet and be once more thrown into a new orbit. A round, faint, nebulous object was found by Spitaler on the evening of May 26, 1884, while he was searching with the twenty-seveninch refractor of the Vienna Observatory for comet 1858 III. Unfavorable weather prevented a re-examination of this part of the sky Astronomical Photography.-In Dr. Gill's photographs of the great comet of 1882, taken at the Cape of Good Hope Observatory, it was found that the stars down to the eighth and ninth magnitude were clearly depicted on the plate. This fact suggested a new method of forming approximate catalogues of the fainter stars by taking photographs of regions of the heavens, several degrees square, and afterward measuring the position of the stars on the plates. The method has been tried at the Harvard College Observatory by Mr. W. H. Pickering. He had in view the construction of a photographic map of the whole heavens, and the determination of the light of the brighter stars. He succeeded in obtaining maps nearly 15° square, containing stars as faint as the eighth magnitude. Should the method prove a success, it is expected that catalogues of the fainter stars can be made with far less labor than heretofore. a Centauri.. Lacaille 9852. € Eridani Possible Influence of Cosmical Dust.-The phenomena of meteors and shooting-stars show that matter is constantly falling upon the earth from space. But science has hitherto furnished no method of estimating the probable quantity of such matter. The dust collected upon the snow in the polar regions has sometimes been supposed to have originated in this way, but this Toucani theory is as yet entirely unproved. Dr. Oppolzer, of Vienna, has recently investigated the question whether the excess of the moon's apparent acceleration above its computed value may not arise from the mass of the earth being gradually increased in this way. By a very careful but somewhat abstruse mathematical calculation he finds that a precipitation of cosmical dust amounting to 2.8 millimetres in a century, over the whole earth's surface (or about a thousandth of an inch in a year), would completely account for the observed excess of the secular acceleration. The question whether a fall of this amount is possible has not yet been considered by geologists. The Krakatoa Eruption, and the Red Skies.-The autumn of 1883 was remarkable for a succession of brilliant sunsets of a very unusual kind, in nearly every part of the world, but more especially in India and the Indian and Southern Pacific Oceans. As the sun approached the horizon, it was seen to assume a distinctly greenish aspect, and an unusual color seemed to pervade the western sky. As a rule, nothing very unusual was observed during the half-hour after sunset. About that time, however, an extraordinary red glow, as from a great fire, began to pervade the western sky, and in some instances actually led to the belief of a conflagration. The phenomenon was first noticed in India, but gradually spread around the whole world. The theory that found most credence among astronomers was that it proceeded from volcanic dust and vapors thrown up at the great eruption of Krakatoa near the end of August, 1883. (See METEOROLOGY, in "Annual Cyclopaedia" for 1883, page 525.) It was found that the course of the red skies around the world followed closely the course that such vapors might be expected to take, from being wafted from place to place by the winds. Additional interest was given to this view by the discovery that self-registering records of barometric pressure, in various points of Europe, showed that an atmospheric wave from the same eruption was carried around the earth. Stellar Parallax.-An important addition has been made at the Cape Observatory to our knowledge of stellar parallax by Drs. Gill and Elkin, working in concert, the latter being the guest of the former at the Cape Observatory. The instrument employed was the fine heliometer made for Lord Lindsey, for the observations of the transit of Venus in 1874. This instrument was purchased by Dr. Gill individually and was brought into use at the Cape in 1880. The following results were communicated to the Royal Astronomical Society in 1884: The most interesting of these results are the first two. The nearest fixed star, so far as we know, is a Centauri, but its distance is shown to be a third greater than was formerly supposed. The actual distance from the above parallax is 275,000 times the distance of the sun, a space which light would require four years four months to traverse. Sirius, though the brightest fixed star in the heavens, is shown to be more distant than several others of the fourth, fifth, or sixth magnitude, and must be regarded as emitting some fifty times as much light as our sun. But the case of ẞ Centauri, a star of almost the first magnitude, is yet more remarkable. Its small negative parallax is impossible, and only shows that its distance is so great as to elude even the refined measurements of Dr. Gill. It can hardly be less than eight or ten times the distance of Sirius, and its absolute brightness must be several times that of Sirius. Parallax of a Tauri.-It does not appear that any attempt has ever been made to measure the parallax of a Tauri, its proper motion being so small that the parallax has been supposed very minute. In preparing his measures of double stars for the press, Otto Struve, director of the Pulkowa Observatory, noticed that they were very favorable for a determination of parallax, and proposed to one of his assistants to investigate the subject. The observations were very accordant in showing a parallax of 0.516". This result, if confirmed, will place a Tauri among the three or four nearest of the fixed stars. Motion of Stars in the Line of Sight.-The spectroscopic determination of the motion of stars in the line of sight, which was inaugurated by Mr. William Huggins, is still continued at the Greenwich Observatory. One result of recent observations is quite inexplicable. The earlier determinations of the motions of Sirius, both by Mr. Huggins and the Greenwich observers, were accordant in showing that Sirius was receding from our system at the rate of some twenty-five miles per second. But, according to the recent measures, this motion has entirely ceased, many observations even showing that the star is approaching us. The reality of such a change in the motion must be considered inadmissible. The Companion of Sirius.-The discovery of this companion is memorable as having been made by Alvan Clark, Jr., in 1862, with the objectglass of the great telescope which had been constructed for Chicago, and as lying exactly in |