extraordinary nature. It appeared like a white spot, of very little density, and without the appearance of a nucleus. It had then only the beginning of a tail, and was not visible to the naked eye. On the 22d January, M. Pons again examined the comet, but what was very singular, it had changed its figure without having changed its place. Though he had not been able on the 21st to take its exact position, yet he had laid down its relative position to the neighbouring stars. Not only was its light more intense, but its tail had changed its shape in the course of a day. It was now two degrees long, and resembled a jet d'eau. M. Pons supposed that its light was rapidly increasing, and that it would soon be seen by the naked eye. Astronomers will readily find it in 0° 30′ of right ascension, and 18° of north declination, near x and u of Pegasus, stars of the sixth magnitude. The preceding comet was re-discovered in this country, by Mr James Veitch of Inchbonny, near Jedburgh, on the 19th of February, when it was distinctly visible to the naked eye, being situated a little to the NW. of Algenib, near to the tip of the wing of Pegasus.

5. Observations of the Solar Eclipse of the 7th September.The following observations of the solar eclipse have been made by Colonel Scherer at St Gall, by MM. Horner and Feer at Zurich, by Oriani at Milan, by Santini at Padua, and by M. Bouvard at Fiume:

The Latitude of St Gall is 47° 25′ 40′, and its Long. 7° 2′ E. of Paris. The Lat. of Zurich is 47° 22′ 27′′, and its Long. 24′ 50′′ of time E. of Paris. 'The Latitude of Fiume is 45° 20′ 10".

See the Bibliotheque Universelle, Novembre 1820, p. 223.

6. Geocentric Places of Pallas from April 1. to July 30. 1821. -The following geocentric places of Pallas have been calculated by M. Staudt :

7. Geocentric Places of Juno, from May 5. to October 20. 1821, -The following geocentric places of Juno have been calculated

8. Astronomical Society of London.-The report of this flourishing institution, which has just been printed, is of the most gratifying nature, and will be read with the highest pleasure by every person who is attached to the study of astronomy, or who takes an interest in the public establishments of his country.

The Council have ordered a die to be formed for striking medals in bronze, silver and gold, as a reward for any material discovery or improvement in the science; and they have specified in their report the different points in practical astronomy to which they wish the attention of the candidates to be more particularly directed. The Society's Gold Medal and L. 21 will be given "for the best paper on the Theory of the motions and perturbations of the satellites of Saturn. The investigation to be so conducted, as to take expressly into consideration the influence of the rings and the figure of the planet, as modified

by the attraction of the rings on the motions of the satellites: to furnish formulæ adapted to the determination of the elements of their orbits, and the constant co-efficients of their periodical and secular equations, from observation; likewise to point out the observations best adapted to lead to a knowledge of such determination. The papers to be sent to the Society on or before the 1st February 1823." The Council propose that each memoir shall bear a motto, and that a sealed paper, having the same motto, shall contain the name of the author. The sealed papers of the unsuccessful candidates will be destroyed unopened, in the presence of the Council. The remaining part of the Report contains an account of their pecuniary resources, which are in a flourishing state; and a notice of the principal points to which the Council requested the attention of Captain Basil Hall, during his voyage to the South Seas.

9. Geocentric Places of Ceres and Vesta.-The following are the geocentric places of Ceres and Vesta for the month of April:

10. Optical Structure of Melted Quartz.-In order to decide the important question relative to the existence of circular or rotatory polarization in the ultimate particles of Silex, which had been maintained by M. Biot, as a demonstrated result of his experiments*, I was anxious to examine the optical properties of a piece of quartz-crystal that had been fused. Upon mentioning my wish to our eminent Professor of Chemistry, he kindly supplied me with a piece of considerable magnitude. This piece, which Dr Hope had reduced to fusion by the action of a stream of oxygen, is nearly two-tenths of an inch long, and

See this Journal, vol. ii. p. 179, 180.; and the present Number, p. 373. VOL. IV. NO. 8. APRIL 1821.

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ths of an inch broad. I now placed it in a fluid of the same refractive power, so that I could transmit polarized light through it in every direction, and, upon a careful examination of its structure, I found that it was entirely destitute both of the ordinary polarizing structure, and of the circularly polarizing structure, having no other action upon light than a piece of well annealed glass. In one corner, a small bubble of air had created, by its expansion, a slight depolarizing structure, such as I have described in this Journal, vol. iii. p. 98. D. B.

11. Singular Properties of Chlorophaite, found in Scotland and Iceland.—In the year 1817 I received from Major Peterson, on his return from Iceland, a mass of amygdaloidal rock, containing what he considered a new substance, and which he had observed possessed the singular property of being perfectly transparent, and of a bottle-green colour, when taken out of the rock, but which became quite opaque when removed from its place, or exposed to the air. I was anxious to ascertain whether this remarkable change was an optical or a mechanical one; and the observations I made put it beyond a doubt that it was of a mechanical nature. The cause of this change may be conceived, by supposing a number of prisms assembled in a particular manner, and kept together by screws, so as to bring their touching surfaces into that close contact which prevents total reflection at the junctions. The mass of aggregated prisms will be now quite transparent; but if we either diminish the compres sing forces by loosening the screws, or suppose some force similar to the disintegrating force of the atmosphere, to act in opposition to the cohesive force represented by the action of the screws, the touching surfaces will be separated, and the whole mass become opaque. We were not aware till lately, that Dr MacCulloch, in his very interesting work on the Western Islands, had discovered, many years ago, in Fife and in Rum the same substance, to which he has given the name of Chlorophæite. He found its specific gravity to be 2.020. It is easily scratched by a quill; is unchangeable before the blowpipe, and is as refractory as quartz. He found it to consist principally of silica, and to give indications of a considerable proportion of iron, and a little alumina. See MacCulloch's Description of the Western Islands, vol. i. p. 504. D. B.

MAGNETISM.

12. Dr Wollaston's Explanation of the Electro-Magnetic Phenomena.-In the Journal of Science, No. XX., Dr Wollaston is stated to have explained the phenomena of the conjunctive wire, (See this volume of our Journal, p. 407.) upon the supposition of an electro-magnetic current passing round the axis of the conjunctive wire, its direction depending upon that of the electric current, or upon the poles of the battery with which it is connected. This explanation will be understood from Plate VI. Fig. 5., No. 1. and No. 2. In No. 1. the current is represented in two sections, at right angles to the axis of the wires when similarly electrified, from which it appears that the north and south powers meeting, will attract each other. In No. 2., the sections of the wire are shewn dissimilarly electrified, by which similar magnetic powers meet, and consequently repel each other.

13. Ampere's Electro-Magnetic Telegraph.-In the curious memoir of M. Ampere, of which we have already given a full account, he proposes to construct a Telegraph, by using as many conducting wires and magnetic needles as there are letters. By placing each letter on a different needle, he establishes, by means of the pile placed far from the needles, an alternate communication betwixt its two extremities and those of each conductor, and thus forms a sort of telegraph, fitted for writing all the details which one may wish to transmit through any obstacle, to a person who is charged with observing the letters placed on the needles. By placing on the pile a row of stops, which would carry the same letters, and establish the communication by their descent, this method of correspondence might be made both easy and rapid.

14. Cause of the Diurnal Variation of the Needle.-In the me moir of M. Ampere above alluded to, he ascribes the Diurnal Variation of the Needle to the alternate change of temperature of the two regions, during the diurnal rotation of the globe, the influence of temperature on electric actions having been established by M. Dessaignes and others. "We must also add," says he, "among the electro-motive actions of the different parts of the earth, that of