Sincey, 0. Subtracting the latter equation from the former -p cos x y (Y + X cos x y) -(y1+p cos xy) (y4-2 Y-2 X cos xy) = 0. By equation (9.) Р 2 2 + X (Y2+Y3—2 Y) cos xy = 0; hence { ( x, − 2/2 ) (Y2+Y3) + p (Y+X cos x y} cos x y -(y+p cos xy) (34-2 Y- 2 X cos x y) = 0. Also by equation (10.) (x, − 2) (Y2+ Y3) + p (Y+X cos x y) = 0; hence (y+p cos xy) (34-2 Y-2 X cos xy) = 0 Y4= p cos xy, or y1 = 2 Y + 2 X cos xy, and it is evident that the circumscribing circle passes through the focus of the parabola. XXIII. On the Position of the South Magnetic Pole. THE By HE experiments detailed by Captain James Clark Ross, R.N., &c., which led to the important discovery of the north magnetic pole, and which are published in the Philosophical Transactions for the year 1834, suggested to me as an object of interesting inquiry, whether any similar affection of the horizontal magnetic needle had ever been noticed by any former navigator of the southern hemisphere, from which an approach to the magnetic south pole could be surmised. No such appearances seem to have been observed by Anson, or any one after him; but prior to his circumnavigation of the globe, Captain Abel Tasman, who was appointed for the discovery of southern countries by direction of the Dutch East India Company, sailed from Batavia with two vessels on the Read before the Royal Society, Feb. 19, 1835; and now communicated by the Author. 14th of August 1642, in his account of the voyage, gives the following particulars of an observation made on the 22nd of November of the same year, when by a prior and subsequent observation of November the 15th and 24th, he was in about latitude 43° S., and longitude from Paris 160°. "The needle was in continual motion without resting upon any of the eight points of the compass," which he says, "led him to conjecture that there were some mines of loadstone on that spot. Tasman's Journal, written in Low Dutch, is now an extremely rare book: a translation of it is given in Dr. Hooke's Philosophical Tracts, p. 179, for the year 1682; in Narborough's and in Correal's Collections of Voyages; and also by Harris, who gives a new translation of it in the second edition of his Collection of Voyages, where, although he notices Dr. Halley's theory of the magnetic poles, which was published in 1683, he does not seem to suspect that Tasman's observation of this very remarkable affection of the magnetic needle was made in the immediate vicinity of the south magnetic pole, at that period in that particular situation, ascertained by the horizontal needle only; the dipping-needle, invented by Norman in 1681, being then unknown."Dr. Halley was of opinion that the north magnetic pole was not far from Baffin's Bay, and that the south magnetic pole was in the Indian Ocean, south-west from New Zealand; whether he had availed himself of the observation made by Tasman in forming this opinion, does not appear. Euler places the north magnetic pole for the year 1757 in latitude 76° north, and longitude 96° west from Teneriffe; and the south magnetic pole in latitude 58° south, and longitude 158° west from Teneriffe. It has been ascertained by observation, that the magnetic poles were on the meridian of the poles of the earth at London in the year 1657, being fifteen years after Tasman's observations, and that it reached its utmost degree of variation west in the year 1818, when it became stationary at 24° 26' west, and has since in respect of London been retrograding towards the east, completing one quarter of the circle round the poles of the earth in 161 years at the rate of 11 or 12 minutes of a degree in a year; so that, presuming Tasman was on the south magnetic pole on the 22nd of November 1642, it would now be found in or about the forty-third parallel of south latitude to the south-east of the island of Madagascar, a convenient situation, when compared with that of the north magnetic pole for ascertaining the exact position of the south magnetic pole, and where experiments with the horizontal- and dippingneedles to lead to its discovery and determine the comparative intensity of the south magnetic power might with facility be Third Series. Vol. 9. No. 52. Aug. 1836. N made. In pursuance of this desirable object the progress of the south magnetic pole might be accurately ascertained by annual observations; whether its distance from the south pole of the earth is uniform in its progress and if in an exact opposite direction to the north magnetic pole; to trace the point at which the axis of the magnetic poles crosses that of the earth; and thus by a continued series of observations and experiments a wide field might be opened to enlarge our hitherto imperfect knowledge of this mysterious power, which might be considered of so much importance in guiding and directing the motion of the earth on its axis and in its orbit. Table of the Observations on the Magnetic Needle made by Captain JOHN ABEL TASMAN from the beginning to the termination of his Voyage; extracted from his Journal. May 6 30 E. 18. 0 26 5 30 E. 27. The needle in conti- Frederick Henry bay. Van Diemen's Land, New Zealand. 147 55 6 12 S. 127 18 Returned to Batavia after 10 months' absence, having sailed round the Australian continent without seeing any part of it but the extremity of Van Diemen's Land. XXIV. On Fluorine. By G. J. KNOX, Esq., and the Rev. THOMAS KNOX,* AS S far as the existence of a substance which had not hitherto been procured in an independent state could be determined, the experiments and reasoning of Davy and Berzelius are sufficiently conclusive. The only desideratum seems to have been the obtaining a vessel upon which this energetic principle would exert no action. Since fluorine shows no affinity for the negative elements oxygen, chlorine, iodine, and bromine, nor for carbon or nitrogen, it would appear that the vessel to contain it should consist of some solid compound of those substances; but as such vessels would be unable to bear exposure to a high temperature, we considered that though they might be convenient for retaining the gas when once obtained, they would not answer for its production. It was therefore necessary to employ some substance already saturated with the element; and for this purpose fluor spar, from bearing exposure to a high temperature and being easily formed into vessels, appeared best adapted. The most convenient method of obtaining the gas seemed to be by acting upon fluoride of mercury with dry chlorine, by which means, if the absence of moisture could be insured and the formation of a chloride of mercury obtained, fluorine must have been disengaged, and if present would be recognised by appropriate tests. Placing dry fluoride of mercury in the fluor-spar vessel, we heated it till a glass plate cooled by the evaporation of sulphuret of carbon showed no trace of moisture in the vessel; the chlorine was then passed through a desiccating tube filled with fused chloride of calcium, the tube being bent at an angle, and its extremity drawn capillary, so as to enter the vessel, which, when filled with the gas, had its orifice closed with a plate of fluor spar which was fastened firmly down. After exposing it to the heat of a spirit-lamp for some time, on removing the fluor spar cover, and replacing it rapidly with one of silica, it showed immediate and powerful action. The inside of the vessel was found on examination to be covered with crystals of bichloride of mercury; both of which results prove the presence of either fluorine or hydrofluoric acid; to determine which, we repeated the experiment, cooling the cover of the vessel so as to condense any hydrofluoric acid which might be present, but none appeared, from • Communicated by the Authors. which we inferred that fluorine and not hydrofluoric acid had been present in the vessel, which was also further confirmed by the absence of fumes when the vessel and its contents had been previously dried. Placing inverted over the orifice of the vessel a clear crystal of fluor spar, with a small perforation in the centre into which a stopper of fluor spar fitted accurately, on the stopper falling into the vessel the tube was filled with a yellowish green gas, the colour of which deepened with heat, and disappeared when cold. On reheating the vessel below, the gas rose again into the crystal above. On removing the crystal while hot to a wet glass plate, it flew to pieces, which prevented us from determining whether the coloured gas was bichloride of mercury under heat and pressure, hydrofluoric acid, or fluorine. Having procured larger vessels with receivers into which ground stoppers were made to fit accurately, we resumed in the present month the experiments we had tried in the beginning of April. 1st Exp. We heated fluoride of lead with oxygen, and afterwards with dry chlorine without action upon the fluoride. When the receiver (its stopper having fallen into the vessel below) was placed over gold-leaf, a chloride of gold was formed. 2nd Exp. Treating hydrofluate of ammonia similarly with chlorine, there was strong action on glass and formation of chloride of gold as before. 3rd Exp. Treating fluoride of mercury with chlorine (as we had done in our former experiments), we obtained crystals of bichloride of mercury in the vessel. Leaving the receiver over gold-leaf, there was after a considerable time action on it, producing a yellowish brown appearance. This we placed on a slip of glass, and on adding a few drops of sulphuric acid and evaporating to dryness there was very strong action on the glass where the gold had been, proving that it was a fluoride of gold, and that since gold is not acted on by hydrofluoric acid there must have been fluorine in the receiver. As an additional corroboration there was no hydrogen in the tube, which there would have been had hydrofluoric acid been decomposed by the gold. From these experiments we conclude that fluorine was present in the receiver, but whether a slight trace of hydrofluoric acid (to which the action on glass was due) may not have been present with it, we have not yet determined. We hope on a future occasion to be able to give particulars with regard to the properties of the gas; but we consider that |