off and carries the picture of the corona out to 60' from the Sun's limb. Thus the pictures made by the Naval Observatory parties cover the whole ground, and are far more complete than those of any previous eclipse. They are not adequately discussed, however, in the volume before us, which is the less excusable as Mr. RANYARD in his recent work on Solar Eclipses has given a practical example of how such work should be done.

Some idea of the fullness with which these collected reports treat nearly everything which can be made the subject of observation may be had by a glance at the subject-index. For example, the contacts were observed at over twenty stations by more than twenty-five observers. Descriptions of the corona are given on thirty-nine different pages, and these do not include the thirty or more drawings. Nearly every one of the phenomena is attested by more than one observer of the many engaged. Thus the corona was seen before or after totality at six stations. Ten persons swept in the vicinity of the Sun for the discovery of Vulcan. Prof. WATSON reports the discovery of two planets, Mr. SWIFT that of two different ones, making four in all, seen or suspected. The report shows that four persons swept over the place of WATSON's (a) without seeing any planet there, and four also swept over the place of SWIFT's two, also without seeing them. In all these cases the telescopes were of adequate power to have shown the objects of WATSON and SWIFT.

The main results of the eclipse of 1878 may be summed up much as follows:

The connection between the activity of the Sun's surface, as evinced by the number and size of the spots and protuberances, and the nature of the corona, has been again shown. The corona in 1878 was far simpler in general character than those of 1869 and 1870. It was observed to extend to a much greater distance from the Sun in this eclipse than in any other, but this is probably due to specially advantageous circumstances. Professors NEWCOMB and LANGLEY both observed the corona with the naked eye, extending 50 or 60 from the Sun's center. There is much difference of opinion as to the brightness of this corona; it prob ably was not materially fainter than that of 1869. Photometric observations were made at Pike's Peak upon this point, but there are no earlier observations easily comparable. The most important point of difference between the coronas of 1869 and 1878 was in their spectra. The bright lines due to the gaseous parts were conspicuous in 1869, while in 1878 they were so faint as only to be seen by a few observers, though these lines were undoubtedly present. A continuous spectrum was seen by most spectroscopic observers. The 1474 line was seen at the beginning and end of the eclipse, but only a few observers saw it during the whole of totality. Prof. EASTMAN traced this line all round the Sun, finding it equally bright at equal distances from the center, and what is remarkable, finding no defect in the brightness of this line in the points

where absolutely no corona was visible to the naked eye or to photographs. No new bright lines were visible in the coronal spectrum. A new line (K. 534) in the chromosphere was discovered by Prof. RockWOOD, who, as well as Prof. YOUNG, saw both lines brightly reversed. Prof. BARKER and others saw the Frauenhofer lines (dark) in the coronal spectrum; they were very faint. The polarization of the corona was observed by several parties. The photographic observations of Professors HARKNESS and WRIGHT show it to be radial in direction. Prof. HASTING'S eye observations give tangential polarization. Such are the main facts of observation to be derived from the volume in question. It is yet too soon to state the bearing of these facts upon existing theories or to deduce any general conclusions from them.

COMETS.

The following comets were visible in 1879:

A. BRORSEN's periodic comet was first seen by TEMPEL on January 14, and on February 26 by TEBBUTT. It passed the perihelion on March 30, and was observed till the end of May. It was found more than a month earlier than Dr. SCHULZE'S ephemeris commenced.

B. TEMPEL'S periodic comet was first seen by him on April 24, and was observed until the end of June. It passed the perihelion on May 7, according to Mr. RAOUL GAUTIER'S elements.

C. SWIFT found a pretty bright comet on June 16, which was independently discovered by WINNECKE on June 21. It was observed till August 23.

D. PALISA discovered a pretty bright comet on August 21, which was seen as late as October 12 (the date of the perihelion passage).

E. Another comet was first seen by HARTWIG on August 24. The last observation seems to be from September 14.

The spectrum of BRORSEN's comet appeared this year very different from what it was in 1868. It consisted of three bands, the central one the brightest, and the least refrangible one exceedingly faint. The wave-lengths as determined by YOUNG, were 468±2, 517+1, and 558 +3. The abnormal character of the spectrum in 1868 (which only one other comet, that of BO RELLY, c. 1877, has exhibited), has therefore disappeared, and the comet has now the ordinary spectrum.*

The following comets were visible in 1880:

Comet A, 1880, was first seen, probably, at the Cape of Good Hope, February 1. It has been usually spoken of as the Great Southern Comet. Dr. B. A. GOULD, of Cordoba, Argentine Republic, says: "It was brightest February 7 or 8, when its length was 40° and its breadth 130, but its brightness not superior to that of the Milky Way in Taurus." Another observer says: "The portion of the tail visible was about 34° in length and 20 in width, its long, straight, narrow form resembling the

*Young, N. xix. 559, Obs. III. 56, Christie N. xx. 5.

one of 1843, which I remember well, although it was inferior in length and brilliancy to that famous comet." February 4 the head of the comet was 3 minutes of arc in diameter, as reported by Dr. GOULD, who also computed the elements of its orbit and found them to agree well with those computed by HIND. The elements of the orbit of this comet agreed very closely with the one of 1843. They are compared below:

Mr. HIND, in communicating these results to the Astronomer Royal of England, says: "Can it be possible that there is such a comet in the system almost grazing the Sun's surface, in perihelion, and revolving in less than thirty-seven years? I confess I feel a difficulty in admitting it, notwithstanding the above extraordinary resemblance of orbits." The appearance of this great comet has again revived the discussions of a resisting medium in space. Prof. OPPOLZER, of Vienna, has published recently two important papers on this theme. TH. BREDICHIN, of Moscow Observatory, Russia, has computed the numerical value of the repulsive force necessary to produce the enormous tail of this comet, and finds it to belong to the same type of those of 1680, 1744, 1769. I am not aware that any observations by the spectroscope were had during the late appearance of this comet.

Comet B was discovered by J. M. SCHAEBERLE, assistant at the Ann Arbor Observatory, April 6, and its train was easily seen, and was three minutes in length. On the 16th it was brighter and larger. Elements of its orbit were computed by SAFFORD, HOLETSCHEK, BIGOURDAN. MARTIN'S elements of this comet are in close agreement with the above.

Comet C is FAYE's short-period comet. It was seen by Mr. COMMON, of England, August 2. It was then extremely faint. The periodic time of this comet is 7.413. It was found by the aid of an ephemeris previously computed.

Comet D was discovered by Dr. HARTWIG, at Strassburg, September 29, and also independently announced by Prof. HARRINGTON, of Ann Arbor, September 30. It was a bright comet, just visible to the naked

eye. "Prof. WINNECKE finds that this comet may be identical with the comet of 1382, 1444, and 1569, as well as that of 1506, and he is led to suggest a period of sixty-two and one-third years as probable."

The spectrum of this comet was observed by KONKOLY, BACKHOUSE, and YOUNG. It gives four bright lines, whose wave-lengths are, respectively, 5,609, 5,492, 5,169, and 4,859 tenth-meters. The spectrum, though faint, was continuous.

October 7, 11, and 12, the spectrum was examined at Greenwich, and was found to consist of the three usual cometary bands, the brightest comparing well with that of alcohol vapor and that of the Bunsen-burner flame.

Comet E was discovered by LEWIS SWIFT, of Warner Observatory, Rochester, N. Y., October 10. It reached its maximum brightness November 16; presented an ill-defined disk several minutes in diameter. The particular feature of interest attending this telescopic comet is that it is identical with comet III of 1869.

Prof. FRISBY, of the United States Naval Observatory, has also computed the elements of this comet from observations by the Washington transit circle. The perihelion distance of the comet appears to be a little greater than that of the earth, and its aphelion is just beyond Jupiter's orbit. These planets may greatly disturb its path in the future. Prof. FRISBY makes its period about five and one-half years.

Comet F was a small bright telescopic object, one minute in diameter, with a distinct central condensation. It was discovered by Dr. PECHULE at Copenhagen; elements were computed by Dr. J. HOLETSCHEK.

Prof. YOUNG observed this comet December 18, 19, and 22, and saw two faint tails. One direct, as usual, away from the Sun, in nearly the opposite direction, and the other roughly toward the Sun, though deflected some degrees to the north. The two streamers made an angle of 150° with each other. "Each was about thirty minutes long on the 18th, and neither was seen after the 22d."

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The three periodic comets whose orbits have been the most carefully examined are ENCKE'S, WINNECKE'S, and FAYE'S. Their least distances from the Sun are 4, 7, 163, of the Earth's distance, respectively. 100, 100, It is well known that ENCKE's original researches indicated the exist ence of a resisting medium in space which, by opposing the motion of the comet through it, gradually shortened its period of revolution. All of ENCKE'S computations were repeated by Dr. VON ASTEN, and his general results confirmed. Dr. MÖLLER, of Lund, executed a like work for FAYE'S Comet, and found no such change in its period and the conclusion was that, granting the existence of a resisting medium, it did not extend so far as one and a half times the earth's mean distance. Dr. OPPOLZER has just concluded a similar investigation for WINNECKE'S comet. He finds that its motion is altered in the same way as that of ENCKE'S comet, and the value of the resisting force is found to be almost

the same as that found by ENCKE. Dr. OPPOLZER goes further and shows that, granting the existence of such a resisting force, its effect upon the motion of FAYE's comet would be so small as to be confounded with uncertainties of the computed perturbations. The question of the existence of a resisting medium will be definitively settled by computations now in progress upon the other comets of short period.

THE PLANETS.

Vulcan (?).—A new attempt to find an orbit in accordance with the more or less doubtful observations of dark round spots passing across the Sun's disk was published in the A. N. by HERR V. OPPOLZER. He found a system of elements which was in remarkably good accordance with the eight observations on which the calculations were founded. WATSON'S observation during the eclipse in 1878 was not among these, and the resulting orbit made "Vulcan" at that moment be 7° preceding the Sun. A nearly central transit ought to have taken place on March 18, 1879, but nothing was seen, though many telescopes were directed to the Sun that day.

In No. 2253-54 of the A. N. Dr. C. H. F. PETERS has published a long article entitled "Some critical remarks on so-called intra-Mercurial Planet Observations." In the first part of this article the writer considers at length the observations made during the eclipse of July 29, 1878, by WATSON and SWIFT, of two unknown objects southwest of the Sun. The fact that the line between the two stars, called a and bby Prof. WATSON, is almost parallel and equal in length to the line between 0 and Cancri, joined to the small size of the improvised circles of the instrument, appears to him to prove beyond doubt that the objects seen were nothing but the stars 0 and Cancri. The constant error of about 3m, which, under this supposition, would affect the R. A.s of a and b, he explains by the different circumstances under which the circle markings were made for the stars and for the Sun; in the former case, in semi-darkness and in a hurry; in the latter case, in full daylight and with leisure. Possibly, also, the markings were made at the same side of the wire-pointer, thus creating a parallax of 20 or 3 of an inch. Mr. SWIFT's observation is treated more summarily by Prof. PETERS, who thinks the confusion and successive gradations in his statements must deprive every reader of confidence in them.

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To this criticism Prof. WATSON has given an indignant reply in No. 2263 of the same journal. He denies flatly that his wire-pointers were as easily bent as supposed by Prof. PETERS, and feels confident that the probable error of 5', assigned by himself, is rather too large than the reverse; the 20' of Prof. PETERS he considers perfectly absurd. There is only one of Prof. PETERS's objections which he did not answer; he did not state whether he saw a and 0 Cancri at the same time or not in this paper. This seems to be the crucial point of the whole question, and Prof. WATSON, in his report to the Naval Observatory, has distinctly