Elements of Lexell's comet by Leverrier. T= 1770, Aug. 13.54085, Greenwich Mean Time of Per. Pass. 356° 16′51′′ Longitude of Perihelion. 2131° 58'56" 66 "Ascending Node. i= 1° 34' 28" Inclination to the Ecliptic. log. q=9.8289491, log. of perihelion distance. e 0.786119, Eccentricity. Motion Direct. "He The comet was discovered by Messier, June 14, 1770. stated," says Mr. Cooper, "that on the night of his discovery, the comet showed a very feeble nebulosity, occupying little space; the centre was brilliant, but it was difficult to decide whether the object was a nebula or a comet. He could observe no relative change of its place in comparing it with fixed stars during two hours. On the night of 17th-18th June, the diameter of the nucleus = 0'22"; that of the nebulosity 5'23"." "On the 29th-30th, the former 1'22", the latter 54', without any sign of tail." From the rapid increase of these angles, as the comet approached the Earth, I judge that they have not been reduced to the unit of distance. Hence it is necessary to compute the Earth's distance from the comet at the date of the observation on June 17th-18th, in order to find po or P1 or p. From Leverrier's elements of Lexell's comet, I have found for June 17.54085, Gr. M. Time, log. r= 0.0731141, and for D, the comet's distance from the Earth at that date, log. D=1.2380469. Hence pD sin (2′ 41.5"). The mass of Lexell's comet is therefore greater than that of the Earth's atmosphere, but appears to be far within the superior limit assigned by La Place. 25. I shall next apply the formula for the limit to Encke's comet. The comet of 1795, discovered by Miss Caroline Herschel, was subsequently recognized as Encke's comet. It was discovered on Nov. 7, 1795, and the discoverer observed that the diameter on that evening was "about 5'." "It had no nucleus, and had the appearance of an ill-defined haziness, which was rather strongest about the middle." I quote from the Notes of Cooper's "Cometic Orbits." On Nov. 21st, Olbers observed the comet, and found its diameter to be "about 3'." I shall therefore take the mean of these determinations, or 4', for the diameter on Nov. 14, 1795. Olbers states that the comet was "round, badly-defined, and without a distinct nucleus." The Elements of this comet, for 1795, were subsequently computed by Encke, and are given by Cooper, as follows: : Perihelion Passage 1795, December 21.44098, Gr. M. T. From these elements and the Earth's place in her orbit, I have found for Nov. 14, 1795, Encke's comet has therefore more than three times the mass of the Earth's atmosphere. 26. I shall next apply the formula for the mass to Halley's comet. Arago says that on January 25, 1836, Sir J. Herschel made two measurements of the head of Halley's comet, as follows: :Diameter of the head in the direction of right-ascension, 229.4" "declination, 237.3" 66 66 66 66 66 66 Two hours after, the measurements were respectively 196.7" in R. A. and 252.0"" Dec. Whether these measurements were reduced to the unit of distance, or not, is not stated. I shall therefore compute the limit of the mass, first on the supposition that they have not been so reduced, and again by supposing that they have been reduced to the unit. I shall take the mean of the first two measurements, or 233.4" for the apparent diameter, which differs only about 41" from the mean of the four. From Cooper's "Cometic Orbits," the elements of Halley's comet are taken, at its perihelion passage in 1835, being the second set of elements computed by H. Westphalen. The inclination, however, has been changed to its supplement, because the motion is retrograde, in order to use Gauss's general formulæ. Halley's comet, perihelion passage Nov. 154.93927, 1835, Gr. M. T. 304° 31′ 34′′ From these elements, and the Earth's position at the date, 1836, January 25a.5, I have found log. 2 (2)3 = 11.9331398 Hence 34.331 log. A 12.3974508 If, therefore, Herschel's observations were not reduced to the unit of distance, IIalley's comet had a mass more than thirty-four times as great as that of the Earth's atmosphere. But if, as is probable, Herschel reduced his measurements to the unit of distance, then I find that Halley's comet had a mass somewhat more than forty-five times that of the Earth's atmosphere; or 45.098. μ A Regarding a comet as comparatively a small mass of gaseous matter, which largely changes its distance from the sun, the preceding analysis shows that the sun exercises a great and constantly varying influence over the comet's figure of equilibrium. As long as any completely closed figure of the comet is maintained, the attraction due to its mass must be superior to the sun's disturbing power. But at the moment when a rupture of the figure takes place in any direction, the sun's disturbing force must then and there be equal or superior to the attraction towards the comet's centre of gravity. On these principles it seems easy to account for the forms of comets, their transformations, and even for their disruptions, as in the case of Biela's comet. Their divisions and subdivisions into swarms of small comets, or meteoric gaseous matter, scattered along the track of the original orbit, are also simple consequences of the same analysis. THE RED SPOT ON JUPITER: OBSERVATIONS UPON ITS PHYSICAL CHARACTER; ITS MAGNITUDE AND THE DETERMINATION OF THE THE great red spot on Jupiter which has attracted such widespread attention from astronomers for two years past was first observed at the Morrison Observatory in July, 1878. During 1879, the spot was observed on about seventy different nights and many observations were made of transits across the central meridian as well as careful observations of its physical appearance and surroundings. The observations were continued until Feb. 7, 1880. Observations were resumed again early in May and are being continued at the present time. The observations have been all made by Prof. C. W. Pritchett with the 12 inch Equatorial of this Observatory and all with the same power, a positive eyepiece magnifying about 280 times. In what follows I shall attempt to give simply a résumé of what has been done, together with the approximate results arrived at in a preliminary discussion of the observations. The rough sketches which are given are intended to give a correct idea of certain phases of the spot and its environment without special regard to finish, or the special detail of the planet's disk. They represent in each case the inverted image as seen in the telescope. In 1878 the spot was seen only once, July 9, at which time a drawing was made and the spot was described briefly as being a rosetinted elliptical cloud." Although sought for the next night and on succeeding nights, when it should have been seen near the center of the disk, nothing more was seen of it during this opposition. For the failure to see the spot during the latter part of 1878 I am at a loss to account. The general appearance of the spot and the physical phenomena of the surrounding surface may be best indicated perhaps by the following extracts from the observing books during 1879 and 1880. 1879, July 2.—Spot observed last year again seen for the first time. The major axis is about one-fourth longer than last year and the minor shorter. Color a bright pink and tinge deeper than that of the belts. 1879, Aug. 8.-At 11.5" Gl.m.t., as for several days past, all the cloud masses called belts seem collected south of the equator except the broad and distinct northern equatorial belt. The surface south of the equator is dense with clouds except in the vicinity of the spot. Here the belt masses seem not to approach. 1879, Aug. 24.-Seeing very fine. For the first time fine red streaks were noticed extending out a short distance from the ends of the spot. 1879, Sept. 6.-A white spot, which was first observed on Sept. 4, is again seen, but much farther to the preceding side, showing a motion either of this or of the red spot. 1879, Sept. 13.-Spot and belts are nearly of the same color (bright pink). The spot is always pink while the belts take all hues from white to ashy, gray, brown and red. 1879, Sept. 20.-The appearance of Jupiter to-night was magnificent. The northern equatorial belt is much redder than the southern which is almost blue. Between the two main belts is an irregular mottled space interspersed with numerous white patches. One white spot just north of the preceding end of the red spot at time of transit. Two small dark cloudlets, one a little preceding, the other following, the west end of the red spot. Far north of the equatorial belt are two very sharp dark lines curving as parallel circles. It is worthy of note that the red spot does not seem to change its position relative to the dark cloudlets above it, while in |