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considerably increased their electricity, and at the same time produced a smell similar to that which is often perceived when the cushion of an electrifying machine rubs against the cylinder." P. 598, 599.

The Aurora did not often appear immediately after sun-set. It seemed that the absence of that luminary, for some hours, was in general required for the production of a state of atmospere, favourable to the generation of the Aurora. On one occasion only (March 8th, 1821), did I observe it distinctly, previous to the disappearance of day-light." P. 599.

"I have never heard any sound that could be unequivocally considered as originating in the Aurora; but the uniform testimony of the natives, both Crees, Copper Indians, and Esquimaux, and of all the older residents in the country, induces me to believe that its motions are sometimes audible. These instances are, however, rare; as will appear, when I state that I have now had an opportunity of observing that meteor for up wards of two hundred different nights." Ibid.



Proceedings of Philosophical Societies.


May 29.-At this meeting, the reading of Mr. W. S. Harris's Account of a Magnetic Balance, and of some recent Experiments on Magnetic Attraction, was resumed and concluded.

The construction of the magnetic balance is analogous to that of the electrical balance, described by Mr. Harris in his Observations on the Effects of Lightning on Floating Bodies, lately published: the experiments made with it were on the laws which govern the force of attraction in magnetized bodies, under different circumstances of distance, &c.

At this meeting, also, the reading of the following paper was commenced: A Case of Pneumato Thorax, with experiments on the absorption of different kinds of air introduced into the pleura; by John Davy, MD. FRS.

June 5.-The reading of Dr. Davy's paper was resumed and concluded.

The case described by Dr. Davy was one of Phthisis Pulmonalis, which proved rapidly fatal, owing to the supervention of Pneumato Thorax. A few hours after death, the chest was perforated under water, and nearly 226 cubic inches of air were collected from the right pleura, into which it had passed by means of an ulcerated opening communicating indirectly through a vomica with the bronchia. This air was found to consist of

azote and carbonic acid; about 94 of the former, and 6 of the latter.

For the purpose of elucidation, Dr. Davy described the results of a number of experiments which he had made on dogs, proving that different gases introduced into the pleura are absorbed with different degrees of rapidity. Nitrous gas, nitrous oxide, oxygen, and hydrogen, soon disappearing, carbonic acid gas more slowly, and azote slowest of all.

Some of the experiments gave rise to the idea that azote was effused into the pleura by the secernent arteries. This subject is discussed by Dr. Davy in connexion with the consideration of the air occasionally found by anatomists in different parts of the body. This air, for reasons which he assigns, he thinks is azote. He does not believe that it is carbonic acid gas, because he has been able to detect the slightest traces of this acid in blood either by means of a high temperature, or the vacuum of an airpump, and because blood contains alkali not saturated with this acid, and is able, in consequence, to combine with an additional portion of it.

At this meeting a paper was also read, on Fossil Shells; by L. W. Dillwyn, Esq. FRS. in a letter to the President.

This paper principally related to the geological distribution of turbinated univalves.

At this meeting likewise, the reading of the following paper was begun: Observations and Experiments on the Daily Variation of the Horizontal and Dipping Needles, under a reduced directive Force; by Peter Barlow, Esq. of the Royal Military Academy, FRS. elect. (Communicated by Davies Gilbert, Esq. Treas. RS.)

June 12.-The reading of Prof. Barlow's paper was resumed and concluded.

A century has now elapsed, Prof. Barlow observed, in the commencement of this paper, since Mr. Graham discovered the diurnal variation of the needle, and, during this period, a number of observations upon it have been made by others, but none of them have led to any decided results respecting the general nature and laws of the phenomenon. Two years ago, the Royal Academy of Copenhagen proposed a prize question on the subject, which has not yet been claimed.

It occurred to the author, that if he could reduce the action of the terrestrial magnetism upon the needle, as mineralogists and others had long been in the habit of doing, for the purpose of detecting very small quantities of magnetism, the diurnal variation would then become more considerable. By pursuing this idea, the most convenient method of executing which he found to be the presenting of one pole of a magnet to the similar pole of the needle, and the opposite pole of another magnet to the opposite pole of the needle, he was enabled successively to increase the diurnal variation from a few minutes to 3° 40', then

to 7° 0', and so on to almost any quantity at pleasure. By approaching his opposing magnets nearer to each other and to the needle, the latter might, moreover, be deflected to any point, and by this means the daily variation observed with the needle in all possible positions. In this way the author found the daily variation, with the north end to the south, to the east, west, &c. &c. and it appeared that the daily change was always greatest. with the needle east or west, and least (indeed imperceptible) when the needle pointed any where near NNW and SSE. From the NNW to south, the principal daily motion was shown by the north end approaching the north, and between the SSE and N, the north end still approached the north and NNW, and, therefore, the motion in the two cases was made in a reverse order. Similar experiments were made on the dipping needle, but the results were not so well marked.

From a comparison of these experiments, Mr. Barlow is inclined to attribute the cause of the daily variation to a change of magnetic intensity in the earth produced by the action of the solar rays, and depending for its amount upon the declination of that body; and consequently on its situation with reference to the plane of no attraction as described in his Essay on Magnetic Attractions, where he has stated his reasons for assuming that the cause, whatever it may be, that gives direction to the needle, is resident on its surface only.

A singular anomaly in the diurnal variation under a reduced directive force, was described in the latter part of the paper: a compass-needle which varied, in Mr. Barlow's house (with the north end of the needle to the east or west), to north, varied, in the garden, from east or west to south. Only three suppositions could be made as to the cause of this anomaly; first, that it might arise from the circumstance that the needle was not exactly in the same relative position with respect to the magnets, &c. in the house as in the garden; secondly, the window of the room where the compass was placed being on the north side, the light might thence affect the needle; or, lastly, was it possible that a stove in the room could experience a diurnal increase and diminution of magnetic power? În order to examine the first of these suppositions, Mr. Barlow carefully measured and determined the position of the needle, &c. in the one situation, and gave them precisely the same in the other, but the discrepancy still remained: he then completely darkened the room for two days, and merely examined the compass with a wax taper, but the former effect was only diminished by this means; the author is of opinion, however, from the result of this experiment, that the light, and not the heat of the sun, will be found the exciting cause of the diurnal variation: in order to examine the third supposition, Mr. Barlow placed a howitzer shell in the garden in the same position with respect to the needle as the stove was in the

house; this changed the period of the maximum effect from eleven o'clock in the morning till four in the afternoon; but the discrepancy continued, and consequently remains unaccounted for. The same difference of variation in the two situations was also found by Mr. Christie, whose house is at some distance from Mr. Barlow's, and who, at the suggestion and request of Mr. B. carried on a similar but totally distinct series of observations, and was led to the same results without being aware that they had occurred to Mr. Barlow.

The following paper was also read: On Bitumen in Stones; by the Right Hon. George Knox, FRS.

The results of Mr. Knox's experiments on the pitchstones of Newry and Meissen, already before the Society (Phil. Trans. 1822, p. 313; Annals, N. S. iv. p. 460), had induced him to submit a great number of other minerals to similar trials. Among these, the following yielded various proportions of bitumen and water Pitchstone, from the Isle of Arran lost 4.705 per cent. by distillation, about 3 of which were bitumen, and the residuum, as in many other cases, was pumice; pearlstone from Tokay, in Hungary; obsidian yielded much bitumen, as did the basaltic greenstone, which forms a vein in the granite of Newry, parallel to that of pitchstone; basalt from Disko Island, and from the Giant's Causeway; wacke from Disko Island yielded 11 per cent. of bitumen; iron clay from Howth; bole from Disko Island; menilite from Menil-montant; adhesive slate from the same place; common serpentine from Zoëblitz in Saxony; mica slate yielded a small quantity of bituminous water; clayslate from Bangor; fetid quartz from Nantes gave 2 per cent. of bituminous water; felspar from Aberdeen, a little.

The following substances sustained no loss of weight by distillation: pumice from Lipari fused; rock crystal underwent no alteration; a colourless crystal of adularia.

Mr. Knox states, as the general result of his researches, that nearly all the minerals belonging to Werner's floetz-trap formation, contain bitumen; and that it likewise exists, but in smaller quantity, and more difficultly separable, in some of the substances which constitute the older rocks.

The paper concluded with some remarks on the new precautions in the analysis of stones, which the author's experiments just noticed seem to indicate the necessity of; since it would appear that the loss of weight by ignition, generally estimated as water, may, in reality, be partly owing to the expulsion of bitumen.

June 19.-As this was the last meeting of the Society for the present session, little more than the titles of the following papers could be read :

On Astronomical Refraction; by J. Ivory, Esq. FRS.

Tables of certain Deviations which appear to have taken

place in the North Polar Distances of some of the principal fixed Stars; by J. Pond, Esq. FRS. Astronomer Royal.

On a Case of Pneumato Thorax, in which the operation of tapping the chest was performed, with additional observations on air found within the body, and on the absorption of air by mucous membranes; by J. Davy, MD. FRS.

On the Length of the Invariable Pendulum in New South Wales; by Sir Thomas Brisbane, KCB. FRS.: communicated by Capt. Kater, FRS.: in a letter to the President.

Astronomical Observations made at Paramatta; by Mr. Rumker: communicated by Sir T. Brisbane, in a letter to the Presi dent.

Of the Motions of the Eye, in Illustration of the Uses of the Muscles of the Orbit; by Charles Bell, Esq. Part II.: communicated by the President.

On Algebraic Transformation, as deducible from first Princi ples, and connected with continuous Approximation, and the Theory of Finite and Fluxional Differences, &c.; by W. G. Horner, Esq. communicated by Davies Gilbert, Esq. Treas. RS. On the Apparent Magnetism of Metallic Titanium; by W, H. Wollaston, MD, VPRS.

In Dr. Wollaston's former paper on the minute cubes of metallic titanium contained in the slag of the iron works of Merthyr Tydvil (see Philosophical Transactions for 1823, Part I.; or Annals of Philosophy for January last, p. 68), he had stated that they were slightly magnetic; for although they were not taken up by a magnet, yet if one of them was suspended by a thread, the action of the magnet would draw the thread upwards about 20°, indicating an attractive force equal to about one-third of the weight of the crystal. By a comparative experiment, he found that 1-250th part of iron would impart equivalent magnetic power to metallic substances, and by repeated solution and evaporation, succeeded in removing so much of the titanium as to discover, in the edges of the precipitate by tincture of galls, the black colour of gallate of iron. It remains a question, therefore, whether these cubes of titanium are properly magnetic themselves, or whether they derive their magnetism from the minute portion of iron which they contain.

An Account of the Effect of Mercurial Vapours on the Crew of H. M. S. Triumph, in the year 1810; by William Burnett, MD.: communicated by Matthew Baillie, MD. FRS.

Contributions towards a Natural and Economical History of the Cocoa-nut Tree; by H. Marshall, Esq.: communicated by Sir James Macgregor, Bart. FRS.

On the Diurnal Variation of the Horizontal Needle, when under the Influence of Magnets; by S. H. Christie, Esq. MA. Mem. Cam. Phil. Soc. and of the Royal Military Academy: communicated by the President.

The President announced some alterations in the statutes of New Series, VOL. VI.


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