I SHALL not here rehearse Dr. Lescarbault's well-known account of his observations on the supposed planet to which this name has been given. The following approximate elements have been calculated by Le Verrier from Lescarbault's rough observations :— do. do. (=1) 18° 16' 19d. 17h. 13,082,000 miles. 3° 36' 6.79 Greatest possible elongation = 8° The application of Kepler's third law gives a remarkable semblance of truth to these elements; but, as will now be seen, additional evidence can be adduced as to the reality of the discovery, much as it has been called in question. On March 20, 1862, Mr. Lummis, of Manchester, was examining the sun's disc, between the hours of 8 and 9 A.M., when he was struck by the appearance of a spot possessed of a rapid proper motion. He called a friend's attention to it, and both remarked its sharp circular form. Official duties most unfortunately interrupted him, after following it for twenty minutes; but he has not the slightest doubt about the matter. The apparent diameter was estimated to be about 7", and in the twenty minutes it moved over about 12' of arc. The telescope employed was 23 inches aperture, and was charged with a power of 80. Mr. Lummis communicated with Mr. Hind on the subject of what he had seen; and the latter, by the aid of the diagram sent, determined that 12' was too great an estimation of the arc traversed by the spot in the time-that 6' would be a nearer value.* Two French calculators attempted to deduce elements from Lummis's observations: the results they obtained, though necessarily very imperfect, are not in the least contradictory, either to each other, or to what has gone before. The first result is adapted from Valz's elements, the second from Radau's. From the heliocentric position of the nodes, it appears that transits can only occur between March 25 and April 10 at the descending node, and between September 27 and October 14 at the ascending node. Instances are not wanting of observations of spots of a planetary character passing across the sun which may turn out to have been transits of Vulcan.† On October 10, 1802, Fritsch saw a round spot pass over the In 3m. it had moved 2', and after a cloudy interval of 4h. had disappeared. sun. On October 9, 1819, Stark saw a well-defined and truly circular spot, about the size of Mercury, which he could not find again in the evening. On October 11, 1847, Schmidt saw a small black point rapidly pass across the sun. On October 14, 1849, the same observer saw a dark body, about 15" in size, pass very rapidly from east to west before the sun. It was neither a bird nor an insect. In the works whence these instances are cited, others are given; but, though suspiciously relating to planets, the dates do not come within the necessary limits for them to have been apparitions of Vulcan, so I do not transcribe them; but they are very interesting, and worthy of attention. It is only right here to state, that M. Liais says he was watching the sun in Brazil during the period in which Lescarbault professes to have seen the black spot, and that he is positively certain that nothing of the kind was visible, though the telescope he em * Month. Not. R.A.S. vol. xxii. p. 232. + Month. Not. R.A.S. vol. xx. p. 100, also p. 192-4; Webb. Celest. Obj. p. 32. ployed was considerably more powerful than that of the French physician. He adds that parallax will not explain matters.* MERCURY. ☀ Mercury is, of the old planets,† the one nearest to the sun, round which it revolves in 87d. 23h. 15m. 43'9s., at a mean distance of 35,360,000 miles. The eccentricity of the orbit of Mercury amounting to o 205, the distance may either extend to 42,609,000 miles, or fall as low as 28,111,000 miles. The apparent diameter of Mercury varies between 4'4" in superior conjunction, and 11" in inferior conjunction: at its greatest elongation it amounts to about 61". The real diameter has been set down at 2,950 miles. The compression, or the difference between the polar and equatorial diameter, has usually been considered to be too small to be measurable, but Dawes, in 1848, gave it at. Mercury exhibits phases resembling those of the Moon. At its greatest elongation (say W.) half its disc is illuminated, but as it approaches superior conjunction, the breadth of the illuminated part increases, and its form becomes gibbous, and ultimately circular when in superior conjunction; at this time the planet is lost in the sun's rays, and is invisible. On emerging therefrom the gibbous form is still existent, but the gibbosity is on the opposite side, and diminishes day by day till the planet arrives at its greatest elongation east, when it again appears like a half-moon. Becoming more and more crescented, it approaches the inferior conjunction; having passed this, the crescent (now transferred to the opposite side) gradually augments until the planet again reaches its greatest westerly elongation. Owing to its proximity to the Sun, observations on the physical appearance of Mercury are obtained with difficulty, and are therefore open to much uncertainty. The greatest possible elongation of the planet not exceeding 29° (and it being in general less), it can never be seen free from strong sunlight, under which conditions it may occasionally be detected after sunset and before sunrise, shining with a pale rosy hue. Mercury does not appear to have received much attention from astronomers of the present day, and the observations of Schröter, at Lilienthal, and of Sir W. Herschel, are the main sources of information. The former observer, and his assistant Harding, obtained what they believed to be decisive evidence of the existence of high mountains on the planet's *Ast. Nach. No. 1281 (Nov. 1, 1860). In case it should be thought that these accounts of the planets are too deficient in statistical data, it may here be remarked that they are intended to be read in connection with tabulated statistics, as it has been thought for several reasons undesirable to encumber these pages with too many figures. surface one in particular, situated in the southern hemisphere, was negatively supposed to come into view from time to time, in consequence of the southern horn, near inferior conjunction, having a truncated appearance, which it was inferred might be due to a mountain arresting the light of the sun, and preventing it reaching as far as the cusp theoretically extended. The extent of this truncature would serve to determine the light of the mountain occasioning it, which has been set down at 10.7 miles, an elevation far exceeding absolutely anything we have on the earth, and in a still more marked degree relatively, when the respective diameters of the two planets are taken into consideration. Schröter, pursuing this enquiry, announced that the planet rotated on its axis in 24h. 5m. 48s. Sir W. Herschel was unable to confirm these results either in whole or even in part. The phases of Mercury are noticeable, as it has sometimes been found that the breadth of the illuminated portion is less than according to calculation it should be. This does not rest alone on the testimony of Schröter, but is supported by Beer and Mädler, from an observation made on September 29, 1832. Mercury is not known to be possessed of an atmosphere; at least, if it has one, it is too attenuated to be detected, as we learn from Sir. W. Herschel, contradicting Schröter and Harding. During the transit across the sun in 1799, these observers, as well as Köhler at Dresden, perceived a small luminous spot on the dark disc, which has been regarded as an indication of volcanic action, an opinion which I cannot but think is expressed on insufficient grounds. (To be continued.) PERIODIC COMETS. (Continued from vol. iii. p. 292.) No. 6.-On June 27, 1851, D'Arrest, at Leipsic, discovered a very faint telescopic comet in the constellation Pisces. Within a fortnight of its discovery, the observations appeared irreconcilable with a parabolic orbit, and it was soon placed beyond a doubt that the true path was an ellipse. The comet was visible for more than three months; but, notwithstanding, the results of the calculations for period were very discordant, and the (predicted) return of the comet in the winter of 1857-8 must be regarded rather in the light of a successful guess than anything else. Sir Thomas Maclear, at the Royal Observatory, Cape of Good Hope, was the only observer of this apparition. M. Villarceau communicated to the Academy of Sciences at Paris, on July 22, 1861, an interesting memoir on the orbit of this comet, which I am induced to place on record (in an epitomised form) in these pages, as it will serve to give the general reader some insight into the nature of the mathematical investigations which the calculators of cometary orbits are called upon to conduct : The perturbations experienced by this comet are owing chiefly to the action of Jupiter, to which it is so near, that during the month of April of the present year its distance was only o'36, or little more than one-third of the Earth's distance from the Sun. Before and after this epoch, Jupiter and the comet have continued, and will continue, so little distant from one another, as to produce the great perturbations to which the comet is at present subject. From a table of the elements of the perturbations produced by Jupiter, Saturn, and Mars, in the interval between the appearance of the comet in 1857-8, and its return to its perihelion in 1864, M. Villarceau obtained the following results: (1.) The longitude of the perihelion will have diminished 4° 35' to August 1863, and will remain sensibly stationary for about a year from that epoch. (2.) The longitude of the node will have continually diminished to the amount of 2° 8'. (3.) The inclination will have increased 1° 49′ to the middle of 1862, and will diminish 6' during a year, continuing stationary during the year following. (4.) The eccentricity, after having increased to the middle of 1860, will diminish rather quickly, and will remain stationary from 1863-5 to 1864-6. "But of all these perturbations," says M. Villarceau, "the most considerable are those of the mean motion and the mean anomaly. After having increased from 5" to July 1860, the mean motion diminishes 9" in one year, and nearly 12" in the year following, remaining stationary in the last year, and with a value 15", 5 less than at its origin. The perturbations of the mean anomaly, after having gradually increased till 1860, will increase rapidly till 1861, when they will amount to 10° 28'; and setting out from this, they will increase 9', and in 1863 and 1864 they will have resumed the same value which they had in 1861." The effect of the first of these perturbations will be to increase the time of the comet's revolution about 69 days; and of the second, to hasten by 49 days the return of the comet to its perihelion in 1864. It will pass its perihelion on February 26, whereas without the influence of these perturbations it would have passed it on April 15. M. Villarceau showed that it would be very difficult to see it on its return. From October 25, 1863, to April 22, 1864, its distance from the Sun was less than 160 or 180, so that it could not then have been seen, its lustre being only 0037 at the first of these dates, and o'089 at the second. By August 22, 1864, it was to have increased to 0035, the difference of longitude between it and the Sun being the 69°. When Sir T. Maclear observed the comet at the Cape in the beginning of 1858, its lustre was o'190, when it was described as very feeble. As was anticipated, the comet escaped notice altogether at its return to perihelion in 1864. FAYE'S COMET, No. 7, was discovered by M. Faye, at the Paris Observatory, on November 22, 1843, being then in the constellation Orion. It exhibited a bright nucleus, with a short tail, but was never sufficiently brilliant to be seen by the unaided eye. That the comet's path was an ellipse, seems to have been suspected independently by more than one observer. To Le Verrier, however, is due the honour of having completely investigated its elements. That astronomer showed that the comet came into our system at least as far back as the year 1747, when it suffered much perturbation from Jupiter,* though it escaped observation during * The intelligent reader may wonder why Jupiter is so constantly called to account as the great bugbear of these short-period comets. The reasons are two in number:-(1) The immense mass of Jupiter compared with that of |