The air was exceedingly calm, and the rupture of the narrow ring was made with the utmost tranquillity, leaving two very sharp cusps. The exterior edge of the Sun appeared in the narrow thread of light, before the rupture, more faint a good deal than the part of the Sun at the opposite point of the diameter of the planet. The blackness of the planet appeared greater a good deal than the usual nuclei of the spots, and its termination persuaded me that the nuclei are really badly terminated, and that there is a real diffusion of matter in their borders. In the intervals left between the clouds, during the passage, I measured a great many distances and positions of the planet from the edge of the Sun's disk; and I made, also, 9 double measures of the diameter of the planet. The result of these is 9"077, with probable error =0"189. It is remarkable that the duration of the passage gives for this diameter 9" 165. This value is different from that given in the tables. A year ago I obtained from some measures a diameter even smaller-that is, 8"-91. I propose to take a few more measures of this element; but it is rather difficult, on account of the termination of Mercury's disk, which is always very bad, and seems to be very faint at the edges. = A new discussion of my magnetical observations compared with a series of electrical atmospherical observations has led 38, 39 me to admit a real connexion between this electricity, and the variations of at least the horizontal intensity. In many things, I think, M. Lamont is right; and what he has suggested on this account I believe him to have demonstrated and seen directly. The Transit of Mercury, November 11, 1861, observed at Malta. By W. Lassell, Esq. At No. 9, Piazzi Slierna, Via Torre, Malta, approximate longitude 58m 2 east of Greenwich, latitude 35° 54′ 46′′ north, 1861, Nov. 11th, I observed the emersion, or egress, and part of the transit of Mercury over the Sun. The best telescope I had at hand was a very sharply-defining Gregorian of 4.7 inches aperture; power used, 78. I first pointed the telescope at about 19.50 Slierna mean time. The planet, being considerably advanced on the disk, appeared perfectly well defined, round. and black. I watched the phenomenon from time to time unti about 22h; after which I observed it uninterruptedly until its disappearance. I had, however, no means suitable for making any accurate measures; but I was filled with admiration. throughout, of the exquisite beauty of the vision. The limb of the Sun and the disk of the planet were far more sharp and beautiful than I have ever seen them with equal power, and within 1 to 3 hours of the horizon. Notwithstanding that the heat of the Sun was so great as to make a shield necessary for the exposed part of my person (though I was generally well protected by a verandah), yet the image was, with occasional slight disturbances, as sharp as can be conceived, and afforded a striking contrast to all I have seen before. I scrutinised the planet well throughout its transit, but could not be sure of any peculiarity. I repeatedly fancied it! a little elliptical, but I do not believe in the reality of the appearance, The times are given in Slierna mean time; they were noted with a duplex watch, compared with a standard mean time clock, accurately corrected and rated by sextant observations. At 22h 15m 571 the planet was estimated to be just its own diameter from the Sun's limb. At 22h 16m 135 it was clearly within one diameter. At 22h 18m 59, first contact. Shortly after, the plane seemed momentarily drawn out towards the limb, pear-like. At 22h 18m 535 the Sun's limb bisected the planet. N distortion whatever. Shortly afterwards I had a momentar impression of the lengthening out of the diameter which was tangent to the Sun's limb, or which had just passed it. At 22h 20m 215, last contact, i. e. the first moment that was sure that the planet was no more to be seen. It has rarely been my lot to observe an astronomical phen menon with circumstances so favourable and pleasant. 39, 40 Prof. CHEVALLIER: on the Transit of Mercury. Observations of the Transit of Mercury, November 11, 1861, made at the Observatory, Durham. By Prof. T. Chevallier. The weather was very favourable, at Durham, for observing the transit of Mercury on the 11th of November. At sunrise the eastern part of the sky was almost cloudless, and continued so till the emersion of the planet. The Sun's limb, however, in consequence of his low altitude and the state of the atmosphere, was very undulating. Mercury was seen upon the Sun's disk immediately after sunrise, his appearance as a round black spot contrasting strongly with that of some ordinary spots on the Sun's surface. The instruments used, in different rooms, were the Northumberland Equatoreal, of 7 feet 4 inches focal length and 5 inches aperture, and the Fraunhofer Equatoreal, of 8 feet 3 inches focal length and 6.5 inches aperture. The internal and external contacts were observed as follows, in Durham sidereal time : Each of these observations was difficult, in consequence of the undulations of the Sun's limb. An instant before the internal contact, the thin curved line of light between the planet and the Sun's limb seemed to break up, by the sudden filling up of the two cusps by a black space. This appearance was, no doubt, occasioned by the tremulous motion affecting the Sun's limb. The exact time of the external contact was rendered uncertain from the same cause. The times, computed from Le Verrier's Tables by the formulæ given by Dr. Schjellerupp (Astronomische Nachrichten, No. 1286), are, 41, 42 Observations of the Transit of Mercury, November 11, 1861, at and near Liverpool. The time was taken from the sidereal clock, which was 333 fast. The fine line of light appeared broken at 12h 33m 98, but it instantly united again, and between 95 and 203 it broke and united several times; after 20° the separation remained permanent. I have taken 145 as the most probable time of interior contact. Contrary to expectation, the last contact was observed with less difficulty than the first; the separation of the planet from the Sun's limb was instantaneous, and may, I think, be depended on to one second of time. Observed with a refractor of 3 inches aperture and 50 inches focal length. The time was taken from a chronometer, the error of which was obtained from the Liverpool Observatory. Egress observed by Matthew Jee, Esq., at Edge Hill, Liverpool: Observed with a Dollond's refractor, 2 inches aperture; power 80. The time was taken from the seconds clock in the office-window of the Magnetic Telegraph Company. This clock is controlled from the Liverpool Observatory. The Transit of Mercury, November 11, 1861, observed at Grantham. By J. W. Jeans, Esq. Morning fine, but rather hazy; a good many light clouds; wind moderate, and atmosphere very tremulous; vision at times good. The first observation I consider very fair, the last rather uncertain; telescope 5 feet focal length, achromatic, 4 inches aperture, reduced to 2 inches; power 80. I was of 42, 43 Mr. BAXENDELL: on the Transit of Mercury. Observations of the Transit of Mercury, November 11, 1861. By Joseph Baxendell, Esq. The following observations were made at Mr. Worthington's Observatory, the instrument used being the equatoreallymounted achromatic of 5 inches aperture and 70 inches focal length. A power of 126 was first applied; but, owing to the unsteadiness of the atmosphere at so low an altitude, micrometrical measurements of the diameter of Mercury were found to be quite impracticable. Two measures of the planet's position on the Sun's disk were taken under a power of 68, but a light cirrous cloud was passing slowly over the Sun at the time, and the images were still very tremulous. The mean result, corrected for refraction and parallax, was as follows: : When the planet was about one-fourth or one-third of its own diameter from the Sun's limb, its form was observed to change slightly; and at the moment of internal contact it was decidedly egg-shaped, the small end of the egg being next to the Sun's limb. The only other feature observed worthy of notice was the excessive blackness of the planet, as compared with the nuclei of the spots then visible on the solar disk. In connexion with the apparent alteration of form of the planet, I may perhaps be allowed to give an extract from my journal, describing a similar appearance observed by my friend Mr. S. W. Williamson, of Cheetham Hill, and myself, on the occasion of the transit of Mercury which occurred Nov. 9th, 1848. The telescope employed was an excellent equatoreallymounted achromatic, of 34 inches aperture and 42 inches focal length, belonging to Mr. Williamson, and the image of the Sun. was thrown on a screen. This image was very well defined, and exhibited the usual features of the solar surface with great distinctness: "At the ingress of the planet a remarkable distortion of its image took place. When the planet had advanced nearly its own diameter on the Sun's disk, the image, instead of immediately assuming a full circular figure, gradually lengthened out on the following side into a pear-like form, until the planet had advanced about one-and-a-half of its own diameter on the Sun's disk, when the projecting part disappeared instanta 43, 44 neously, and the Sun's light closed round the planet, exhibiting it removed a very sensible distance from the limb of the Sun." As the apparent diameter of Mercury, when on the sun' disk, is probably diminished by the effect of irradiation, th alteration of its form, on approaching or leaving the limb, a noticed by some observers, may perhaps be due to the dimi nished effect of irradiation consequent upon the rapid diminishing intensity of the Sun's light near the limb, and t the greater susceptibility of some eyes than others to the effect of irradiation; and I may remark that, to my own eye, the degradation of the light of the Sun's disk near the borde whether seen directly through the telescope or projected e a screen, is always very strikingly evident. Manchester, Dec. 12, 1861. On the Elements of the Variable Star R Sagittæ. This star was discovered to be variable in October, 1859 and in a notice of it which I communicated to the Physica Section of the Manchester Literary and Philosophical Society on the 5th January, 1860, its period was stated to be abor 74 days, and its range of variation to be from the g magnitude at minimum to the 8.4 magnitude at maximum The observations which I have since made have, howeve enabled me to determine its elements with much greate: accuracy than could be expected in a first approximation and have also shown that it merits attention as being one c the very few but interesting variables, the light-curves wherect exhibit a distinctly marked secondary minimum. Many o the variables occasionally exhibit decided deviations from the ordinary course of their changes; but the cases are very rare in which a secondary minimum forms a permanent feature in the curves laid down from observations extending over severa successive periods. During the two years which have elapsed since I first noticed the variability of R Sagittæ, I have obtained the following determinations of the times of nine of its principal minima : These differences show that the variations in the length of the period of R Sagittæ are confined within moderate limits, and that this star may be ranked in the class of moderately regular variables. Using the mean period of 70-88 days in combining all the observations made in the different phases of the star's changes, and projecting the mean results in the usual way, I find, from the curve thus obtained, that the principal maximum, the secondary minimum, and the secondary maximum, follow the principal minimum in 17, 35, and 44 days respectively. It appears, therefore, that the interval between the principal and the secondary minimum is almost exactly one-half of the whole period, precisely as in the case of the well-known double-period variable, ß Lyra. 8:45 6 10 24 23.6 = 8.95 6 10 44 50'5 8.60 7 10 24 25 2 7 10 54 53°7 7 II 25 214 8 10 58 56.3 8 II 24 130 Sept. 10 12 11°3 I 10 37 87 On the Variable Star R Vulpecula. By G. Knott, Esq. R Vulpecula. Piazzi xx. 457. My earliest observations of this variable were made on the 7th, 9th, and 10th of September, when it shone as a star of the 9.3 magnitude. Bad weather and absence from home prevented another observation till the 26th of the month, when, to my surprise, I found it considerably fainter, and of the 117 magnitude. Since that date I have kept the star pretty constantly in view; and the discussion and projection of my observations give October 27th as the epoch of minimum, just two days prior to the date of probable maximum, as given in Mr. Pogson's ephemeris. The magnitude at minimum appears to have been about 13.6. As this is the first communication I have had the honour of submitting to the Astronomical Society, it will probably be deemed desirable that I should briefly describe my instrument and method of observing variable stars. My Observatory is furnished with a 9-foot equatoreal, the object-glass by Messrs. Alvan Clark and Sons, and of 7 inches aperture. It was formerly in the possession of the Rev. W. R. Dawes, and was very favourably spoken of by him—a sufficient guarantee of its quality. I usually employ an excellent positive eyepiece, constructed for me by Mr. Dollond; it has a large field, and gives a magnifying power of 60, as determined by measuring the emergent pencil. Higher magnifiers are occasionally employed. 1860 165. Decidedly less than & Centauri; about equal to d Crucis. 1860 287. Equal to d Crucis; not much greater than @ Argus. 1860 972. A little less than & Crucis. Argus. Argus. Taking the observations in groups according to the brackets, and using Sir John Herschel's photometric magnitudes for the reference-stars, the following approximate table is obtained. Where a star of reference does not occur in Sir John Herschel's list (as is the case with d Crucis, for example), 4 has been added to the ordinary magnitude, to bring it to the photometric scale. Photometric Mag. Mean Solar Time of Observation. Irene 70 56 8.14 72 2 22.22 72 10 22 27 73 26 7'39 N.P.D. from Observation. R.A. from Observation. h m 2 24 59'11 86 54 23°36 86 47 6:18 h m 1861, Nov. 2 87 5 52°52 |