May 1823, at the Cape of Good Hope, when the sun's disc was just dipping in the ocean. On either side of the true luminary, and within the breadth of a degree and a half of his disc, four mock-suns appeared on the left, and three on the right. They had the same shape as the true sun, touched the water at the same instant, and all of them disappeared together, shining as bright spots upon the water's edge. It was a delightful evening, without a cloud; the barometer was 30.2 inches and the thermometer 64° F. This most probably was an instance of lateral mirage. 266. According to Dr Thomas Young, parhelia and paraselena, with their accompanying luminous circles and segments, depend upon the combined reflexions of the solar or lunar rays, from the facets of snowy prisms floating in the atmosphere, a theory which, in the 17th century, was entertained by Huygens.' When the snowy crystals are at the same time prismatic and lamellated, the rays suffer both refraction and reflexion, and a combination of excentric circles results. 267. The first or internal solar circle, is produced in the same manner as the artificial halos which we have explained, through prismatic crystals of ice and snow floating in the air, giving rise to a halo whose radius is nearly 22°, having the red within, and vivid in proportion as the ray strikes the crystal at the minimum angle of deviation, for there is a position. in which the prism may be placed, so that the incident angle may be varied without producing a corresponding change in that of refraction. The second or exterior solar circle,-the extraordinary halo,-is concentric with the former, less vivid, and distant from the sun about 46.5°; the red is internal: its explanation is less easy than that of the former. According to Galle, it arises when the icy prisms are terminated in hexagonal planes at right angles to the lateral faces of the crystal, through which diedral angles, in the proper position. of the crystal, the light suffers refraction. Cavendish suggested that this halo arose from refraction by the terminal right angles of the prisms. Were it, as Young and Brandes Dissert. de Corn. et Parhel.; Smith's Optics, vol. i. Q suppose, the effect of refraction through two prisms, one behind the other, the radius of the circle would be nearly 44°, which it is not; consequently, we must adopt another hypothesis, and the suggestion of Cavendish, and theory of Galle, explain the phenomenon. Besides these, a third concentric solar circle is sometimes, but rarely, met with; it is much larger than the others, having a radius of 90°, and the red external. In this case the ray of light suffers refraction, after reflexion by the posterior surface of the hexangular prism. 268. The tangental or circumzenithal arcs arise from refractions through horizontal prisms. Galle' explains that of the second or extraordinary halo,—the circumzenithal external arc, by refraction through prisms the axes of which are vertical to the horizon, the light impinging upon one of the facets and emerging by the hexagonal termination below. 269. The white-coloured parhelic circle which passes through the sun and runs parallel with the horizon, is, according to Dr Thomas Young, derived from the reflexion of the vertical prismatic facets of the crystals which are floating at all azimuthal distances. Fraunhofer and Schmidt consider it the consequence of diffraction. 270. The parhelia result, according to Young, from two refractions and an intermediate reflexion within the same prism. They are rarely met with opposite the sun in the great horizontal circle, but frequently at the intersections of this and the other circles, and the meetings of the latter halos with the tangental arcs,-not exactly in, but a little beyond the circle, and distant from the sun in proportion to the altitude of that luminary. According to Bravais, the amplitude of this lateral deviation is inappreciable when the sun's altitude is zero, but it amounts to 18' at that of 10°, to 1° 13' at that of 20°, to 3° 2' at that of 30°, and to 5° 46′ at that of 40°. 271. Paraselenæ are frequently met with, but less often than parhelia. Five moons were seen at once, in Yorkshire, at the commencement of a severe winter in the year 1200:2 two appeared in the winter of 1215. Hevelius observed this 1 Poggend. Annalen, xlix. 261. 2 Hol. vol. iii. p. 163. meteor at Dantzic, on the 30th March 1660; it lasted nearly three hours. Around the moon were two concentric circles with tangental arcs; the paraselenæ appeared in the inner halo, to the east and west of the true moon, and from them issued tails which extended as far as the external circle. Again, on the 17th December, in the same year, he saw a similar phenomenon, which continued from 6.5 A.M. till sunrise. About 22°. 5 from the moon there was a prismatic circle, cut by the horizon and tipped by a tangental arc; opposite the moon, north and south, two paraselenæ appeared with luminous tails, and at the intersection of the arcs a third image was visible. In addition, a white and bright cross with the moon in its centre, pointed three of its limbs to the mock-moons and the fourth to the horizon; in the angles close to the moon, there was a corona, upon which the cross seemed to be projected. Muschenbröck has recorded a fine. example. On the 12th of April 1816, at 9 P. M., two paraselenæ were seen from the Observatory at Prague, by David; the meteor lasted about an hour. Forster records one seen on the 30th July 1817, at 11.5 P.M. Two are mentioned by Burney' as witnessed in November 1818; seven in 1819; and ten in 1820. Several are recorded by Fisher, seen in the arctic circle. On the 1st January 1820, at 11 A. M., he observed a halo 45° in diameter, intersected by two luminous columns of a yellowish-white colour, which crossed the moon at right angles and were equal in breadth to her disc; these columns, as they approached the halo, tapered to a point, and Journal passim. 1 Ann. of Philos. xvii. 365. in their meetings with the prismatic circle, mock-moons were visible, the two horizontal ones having a long tail extending beyond the halo. Dr Traill' observed a paraselene, at Liverpool, on the 30th of March in the same year, about 10 P.M. On the 25th October 1825, two circles were observed at Kensington, about 10.5 P. M., the one circumzenithal and the other around the moon, but no image of our satellite was seen at their intersections. Several paraselenæ were seen in 1827 in Bedford." A similar meteor was witnessed by Mr Birt' on May 6. 1841; on September 25. same year, two paraselenæ were visible; on May 1. and October 20. 1844, similar meteors were seen by Mr Lowe." A fine meteor of the same kind was seen by Professor Page" on the night of April 19. 1845. On the first of June 1847, between the hours of 11 and 2, a luminous circle surrounded our satellite, on which were two paraselenæ, one on each side of the moon. A partial appearance of this meteor was witnessed by Dr Armstrong of South Lambeth, on the night of the 25th February 1842. The moon was that day full and rose about 7 P. M. When at an altitude of nearly 10°, a bright belt crossed her disc, of the same apparent diameter, perpendicular to the horizon, uniformly well defined, and terminating at each end in a small cirri-stratus cloud; at 8 o'clock it shortened at the upper extremity. Its edges underwent no diminution in brightness, but inclined 45° to the moon's horizontal diameter, preserving this position till the phenomenon had entirely vanished. 272. Cassini, Lattire, Feuillée, and others, mention having seen the sun rise and set with a perpendicular column of light, projecting sometimes upwards, at other times downwards, to the distance of 6°, and the breadth of his disc. Mr Ellis at Churchill, Hudson's Bay, observed the sunrise heralded by two long columns of red light about 20° distant on either side. Just as his disc had risen, these luminous beams converged forming an arc, with a kind of parhelion over the true 1 Ed. Phil. Jour. vol. iii. P. 402. Unit. Ser. Jour. 1829, i. 367. 2 Ann. Phil. xxviii. 236. Ib. vols. 25 and 26. Phil. Mag. No. 121. 7 W Poole Herald. sun. These streams of light, he says, are connected with two other parhelia which rise with the sun, and in the winter season accompany him during the day, disappearing with him in the evening. A phenomenon of this kind was seen at Toula in Russia,' in July 1819. Captain Lyon' describes a singularly beautiful appearance, which he saw in the arctic regions, on Nov. 20. 1821. Previous to sunrise a spiral ray of delicate pink shot from the horizon, and increasing in size and brilliancy, reached the zenith, at which time its form was that of a blowpipe flame. On the appearance of the sun, the whole eastern sky partook of the rosy hue, and the snow, ships, and entire scenery, became warmly illuminated until his whole disc had risen; then the usual grey tints of morning assumed their accustomed place, the scene becoming doubly desolate by a fall of snow. This meteor was seen by Lohrmann, at Dohna, near Dresden, on the 8th of June 1824, at 8 P.M.; it was visible in other parts of Germany, and frequently afterwards the same phenomenon was witnessed. The sun was setting behind the mountains when a luminous column 1° wide and 30° high, rose above the position of his disc; it continued some time, and rapidly disappeared in the shades of night. Professor Kämtz had an opportunity of studying this meteor in January 1838, when the sun was preceded by a column about 10° high, which continued for several hours; when he had mounted 6°, an analogous band was observed beneath his disc, with this peculiarity, that the lower column appeared to reach the ground where the observer was standing. The phenomenon lasted till about noon; during its continuance, a portion of the halo whose radius is 22°, was once noticed in the east. Numerous spiculæ of snow were floating in the atmosphere at the time. Professor Christie' mentions having several times observed, in the south of England, a vertical yellow ray extending upwards from the sun, of the same diameter throughout, and rising to an altitude of 30°, diminishing in brightness with its altitude. Lord Valentia mentions having seen the sun set at Mocha in Arabia, in 1 1 Ann. of Phil. xx. 223. 2 Jour. Lond. 1824. 3 Kamtz and Martins,-Met. Brit. Assoc. 1837; Athen. No. 519, p. 747, Oct. 7. 1837. |