true bearing of the latter being S. 13 W. Thus the magnetic fluid seemed on this spot to have less influence on the needle than on the spot where its power was first observed; and at a short distance from the base of the hill, the needle regained its natural position. The rocks, when broken, were of a dark iron-grey: they did not appear to contain any iron, for when tried at the tent, the magnet had no power over them. I could not discern any regular stratum of rock, the hill being covered with large detached stones, many of which form figures of five and six sides.

The variation of the needle was observed by azimuth to be 6° 22′."

Having again ascended Loadstone Hill, Mr Oxley repeated the above experiments with the same results. "Several different stations on the summit ridge were tried, and the needle was variously affected. The spot where the phenomenon was_first observed, seemed to have the greatest effect on the needle. A common sewing-needle was strongly rubbed with a magnet, and balanced on the point of the rock, when it was much agitated, and the point flew round from the north to the south. The needle of the circumferentor, taken out of the box, was affected in a similar manner, only that when balanced on the rock, the fluid did not possess sufficient power to turn the point more than one point of the circle instead of quite round, as when balanced in the compass-box. A compound magnet was laid on the rock, and applied to it in different ways; but it did not seem in any manner affected by the power which had so surprised us with its effect on the compass." "The observations. made here placed us in Lat. 31° 13′ S., Long. 148° 41′ 30′′ E., and I estimate the mean variation to be about 7° Easterly. We found that no reliance could be placed on bearings taken with the compass on heights in this vicinity, and I am fearful that the bearings taken from Mount Exmouth will require verification, a difference of 4° being observed in some, when compared with other bearings, which could not be supposed to be affected by the magnetic fluid."

ART. XXX.-Reply to a Note in the Annales de Chimie by M. ARAGO, on the Phosphorescence of Fluor-Spar.

IN the Annales de Chimie et de Physique for July 1820, p. 297.

the Editor has done us the honour to translate the paper On the Phosphorescence of Minerals, published in the 1st Volume of this Journal, and also the Notice in the 2d Volume, On a Singular Developement of Crystalline Structure by Phosphorescence. To the translation of this last notice, M. Arago has thought proper to add the following harsh observations, without taking the trouble of understanding the notice to which it is appended:

"Note du Redacteur.-Je laisse au lecteur à juger s'il n'est pas au moins extraordinaire, qu'après avoir remonté jusqu'a Benvenuto Cellini, pour tracer l'histoire des recherches que les physiciens ont faites sur la phosphorescence des mineraux, M. Brewster ne se soit pas ressouvenu d'une note de Pallas, qui a été inserée en 1783, dans le tome 1er des Mémoires de Petersbourg. Je vais reparer cet oubli.

"M. Pallas nous apprend que le spath-fluor de Catherinenbourg devient lumineux à la simple chaleur de la main, lorsqu'on l'y tient renfermé une demi-minute seulement. La lucur que le cristal repand alors est blanchâtre et pale; à la chaleur de l'eau bouillante, cette lueur verdit; par un temperature plus elevée, la lumiere phosphorescente passe d'un vert celadon au plus beau bleu de turquoise; phenomenes que les fluors communs n'offrent pas.

"La couleur generale du filon est un violet pale; on voit par-ci par-là des parties plus foncées; ailleurs on remarque des couches d'une transparence blanchâtre tirant par fois sur le vert. Ce sont les veines verdâtres qui jouissent au plus haut degré de la vertu phosphoriques, et qui passent par la chaleur au bleu le plus vif. Dans le fluor qu'on trouve à la montagne d'Ouboukoun, près du Selenga, et dans ceux de Breintenbrunn en Saxe, qui sont veinés de vert sur un fond violet, les veines vertes deviennent lumineuses par un chaleur mediocre, tandis que le reste

3

n'emet aucune lueur sensible, et quelquefois n'est point phosphorique de tout."

The preceding passage, which we have printed literatim as it stands in the original, evidently contains two charges, the one expressed, and the other implied. The expressed charge is, that I have very strangely omitted to quote Pallas's experiments on phosphorescence; and the implied one is, that Pallas's paper contains the same discovery which I have announced in my notice On a Singular Developement of Crystalline Structure by Phosphorescence.

The first charge is unworthy of notice; as an author is entitled to give, as he pleases, either a short or a copious history of the subject of which he treats. The experiments of many other philosophers are omitted, as well as those of Pallas; and the blame of omitting his name, must be shared with Mr Wedgwood, Haüy, and every other writer on the subject that I am acquainted with.

The other charge, which was intended to be a more 'serious one, is founded on an utter misconception of the result announ❤ ced in my notice, arising, it is to be hoped, from an imperfect acquaintance with the English language.

The result obtained by Pallas may be thus expressed: "In the fluors of Ouboukoun, &c. which have green veins on a violet ground, the green veins are phosphorescent with a moderate heat, and the violet part is opaque." Now, it was known to all the world, that green fluor gave out a green light, and blue fluor sometimes a differently coloured light; and every child who has amused himself with heating some of the Derbyshire spars, which are generally blue and green, could not fail to notice, that the green gave out one light, and the blue a different light, or perhaps none at all. This fact I have observed repeatedly; and if I had published it as a new discovery, I might have been justly reminded, in the usual language of civility, by those who had a tender regard for Pallas's reputation, that he had anticipated me in this fact.

The result, however, contained in my paper, is very different from this. I take a piece of fluor-spar, which has perceptible veins in one part, and no appearance of them in another: I place it on

a hot iron, and directing my attention to the part without veins, I find that the phosphorescent matter is arranged in strata or veins, (although no veins are seen), and upon looking to the part with veins, I observe, that the veins rendered visible by phosphorescence are parallel to the veins visible to the eye. In this experiment, I pay no attention to the phosphorescence of the veins visible to the eye; but I remark, that each stratum (not the strata visible to the eye, but the strata rendered visible by phosphorescence) emits a phosphoric light peculiar to itself. If any ground for misconception existed, it was entirely removed, by comparing the effect now described to that produced in a piece of chalky Tabasheer, of an uniform whiteness, where a veined structure is exhibited, after the partial discharge of the oil which it had unequally absorbed.” Will the reader believe, that these three lines, though containing a curious fact, and highly illustrative of the subject under discussion, are not only omitted in M. Arago's translation of my paper, but are the only lines in it that are omitted *?

If the object of my notice had been to communicate the fact, that a veined structure gave a veined phosphorescence, it would have been entirely inconsistent with the title of it, which expressly states, that it is upon a Singular DEVELOPEMENT of Crystalline Structure by Phosphorescence; and when I found a veined structure thus luminously displayed, where the eye could not discern it, I had recourse to a microscope, and even then I found that the phosphorescence exhibited veins which could not be detected by the application of that instrument.

But let us suppose that my notice had nothing to do with the developement of crystalline structure, where it was not otherwise apparent, and let us suppose that it was only, like that of Pallas, a simple experiment on veined fluor-spar. Even in this point of view, it contains a new result. Pallas observed in a piece of violet spar, with green veins, that the green veins were phospho

That these lines were intentionally omitted, is very obvious; for in the paragraph which precedes the translation of my notice, the Editor says, "En voici la substance." But instead of the substance, he has given the whole notice, excepting the three lines on tabasheer! The Editor had perhaps some good reason for keeping the word Tabasheer out of the Annales de Chimie.

rescent, and the blue part opaque, whereas I observed three dif ferent colours, besides the opaque portion, namely, purple light, yellowish-green light, and whitish light; and I venture to say, that the sight which I saw has never been described, and is one of the most splendid exhibitions of a natural phenomenon that can be witnessed. Had not my description of the experiment been printed the day after it was made, and when all the Plates of the Journal were thrown off, I should have given an engraving of it, which would have represented one of the finest patterns of the kaleidoscope, drawn with phosphoric light, and displaying the whole crystallographic structure of fluor-spar,-a structure, too, which could not be seen either by the naked eye, or by the aid of a microscope.

But beside the novelty and splendour of this phenomenon, we may claim for it a higher character, as it has led to the determination of the only general point which has been ascertained respecting the cause of phosphorescence, and which we shall be able to lay before our readers in a subsequent Number.

Here we intended to have concluded these remarks; but it naturally occured to us, that as M. Arago had given a garbled translation of my notice, by leaving out an important part, which tended to overturn his view of the matter, he might also have given a false quotation from Pallas. I therefore lost no time in procuring Pallas's Memoir, which was published in 1787, in the Petersburg Memoirs for 1783, and I found my suspicion completely verified *.

• In order that the reader may judge for himself, I shall give in this Note the whole of Pallas's Memoir.

"Sa Majesté Impériale ayant remarqué Elle-même que des échantillons d'un spath fluor, récemment envoyés de Cathérinenbourg par M. le Gouverneur-Général Kaschkin, possedent non seulement un degré supérieur de la vertu phosphorique que l'on connoit à plusieurs espéces de fluors, au point de devenir lumineux dans l'eau chaude; mais aussi que la lueur phosphorique qu'ils répandent à une chaleur plus forte passe d'un verd séladon au plus beau bleu de turquoise, phénomène que les fluors connus n'offrent pas cette Grande Souveraine, toujours attentive à l'avancement des Sciences & gracieusement disposée envers Son Academie, m'a chargé de remettre à la Conférence un bel échantillon de ce fluor nouvellement découvert, avec plusieurs petits, qui peuvent servir aux expériences.

"Le grand échantillon, destiné pour le cabinet académique, montre clairement, que ce fluor s'est trouvé en filon, de la largeur d'une main, dans une gangue micacée dont les deux salbandes montrent des restes. La couleur de la plus grande