In addition to the figures there stated, I should wish to present those Gentlemen, who have turned their attention to the simple and beautiful theory of spherical particles, with a cube to be extracted from a tetrahedron, similar to that described in the Lecture, capable of being held together by the most simple power of attraction, and possessing four pair of poles, which possibly may account for the phenomena discoverable in the boracite.

If from a tetrahedron consisting of seven layers a tetahedron be taken from each solid angle of three layers deep, then will remain an octahedron having four spheres in each edge, and a single one in the centre of each face, which is the corner of a cube contained in the octahedron ; and should five spheres be Temoved from each solid angle of the octahedron, a cube will remain, constructed exactly upon the same principle with the tetrahedron and iby

The easiest octahedron.

to make this cube is to take a tetrahedron consisting of ten spheres, and place one sphere on the centre of each face, which will produce exactly the same figure.

Should you think the above account of sufficient importance, your insertion of it in the Annals of Philosophy will great oblige, Sir, your most obedient servant,

N. I. LARKIN.

ARTICLE XV.

Proceedings of Philosophical Societies.

ROYAL SOCIETY.

ON Thursday the 1st of July a paper by Sir Humphry Davy was read, containing farther observations on the new detonating compound of chlorine and azote. After recovering from the accident which happened to him during his original experiments on this substance, Sir Humphry made a variety of experiments to determine its properties and composition. Its specific gravity is 1.623. When in contact with water, it congeals at about 40°; but this does not happen when it is kept separate from water. It detonates in nitric acid, and in ammonia; gives out azote in muriatic acid, and is likewise decomposed in sulphuric acid. Attempts were made to decornpose it in exhausted glass vessels in the state of vapour; but they were unsuccessful. In

The removal of the solid angles of the octahedron is only for the purpose of demonstration, and is by no means i: tended to convey an idea that any natural crystal of this shape is inclined to split in that direction, the impossibility of which has been ably proved by Dr. Wollaston.

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general, the glass was broken by an explosion; and when that did not happen, the proportion of chlorine and azote evolved could not be determined, on account of the unknown proportion of atmospheric air that remained in the vessel. When the detonating compound is brought in contact with mercury, a white powder is formed, and azotic gas disengaged. In one experiment a detonation took place, which obliged him to work upon smaller quantities. The white powder was found to be a mixture of calomel and corrosive sublimate; and it sublimed entirely without the disengagement of any gas, indicating the absence both of hydrogen and oxygen. Muriatic acid does not destroy the colour of solution of indigo in sulphuric acid; but if it be impregnated with chlorine, it destroys a determinate quantity of the blue colour, according to the proportion of chlo rine present.The same thing happens when the detonating compound is dissolved in muriatic acid. This furnished a method for determining the proportion of chlorine contained in the detonating compound. The result of all these methods of analysis is, that the detonating compound is composed of

reckoning by weight, or if we reckon by bulks of

Sir H. Davy proposes to call this detonating compound

azotane.

At the same meeting were read some observations on a new comet, observed by Capt. Hill, in the Hon. East India Company's service.

On Thursday the 8th of July the following papers were read: 1. A catalogue of the positions of a number of circumpolar stars by the Astronomer Royal, Mr. Pond.)

2. Au analysis of a substance thrown out of Mount Vesuvius, by James Smithson, Esq. This substance had been sent to Mr. Smithson when in Italy in 1794, in order to determine its nature; and he ascertained, by a number of trials, that it consisted chiefly of sulphate of potash. This result was published soon after in an Italian Journal, but no subsequent notice was taken of it by mineralogists. Mr. Smithson was induced to examine it with more accuracy lately, and the result of his experiments is, that it consists of sulphate of potash, sulphate of soda, sulphate of ammonia, muriate of ammonia, muriate of copper, and muriate

of iron, with some earthy matter. Mr. Smithson, by way of introduction to his paper, gives a view of his opinions about the origin of the earth. In his opinion, it was originally a sun, or a comet, and was brought to the state in which it is at present by undergoing combustion at the surface. The volcanoes are the relics of this original combustion, and the materials were the metallic bases of the earthy substances of which the primitive strata are composed. As a proof that these primitive strata have been formed by combustion, he mentions that garnets, hornblende, and other crystals found in them, contain no water, and that little or no water is to be found in the primitive strata themselves. yns sug of obliaruq son o

3. Observations by Dr. Marcet on the cold produced by the evaporation of sulphuret of carbon. This liquid evaporates more rapidly than any other, and produces in consequence a greater degree of cold. A spirit of wine thermometer, having its bulb surrounded with cotton cloth or lint, if dipped into sulphuret of carbon, and suspended in the air, sinks from 60° to 0. If it be put into the receiver of an air-pump, and a moderate exhaustion be made, it sinks from 60° to 81° (I have seen it myself in these circumstances sink from 74° to -972°). If a tube containing mercury be treated in the same way, the mercury may be readily frozen, even in summer. The drier the air in the receiver is, the more easily is the cold produced. Hence the presence of sulphuric acid may be of some little service in removing the vapour from the air in the receiver previous to exhaustion; otherwise it occasions no increase of the cold. G

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4. Observations on the composition of fluor spar, and on its acid basis, by Sir Humphry Davy. The author begins his paper with an historical detail of the attempts made by himself, and Gay-Lussac and Thenard, to decompose fluoric acid, and the ill success of these attempts. It appears from the compounds into which fluoric acid enters, that the weight of an integrant particle of it does not exceed 1.05, supposing an atom of oxygen to weigh 1. Hence it follows that if it is a compound of oxygen and an inflammable base, the base can only have the 20th part of the weight of the oxygen. This supposition he considers as unlikely to be correct. He therefore supposes that fluoric acid, like muriatic acid, is a compound of hydrogen and an unknown supporter of combustion, to which he gives the name of fluorine. He relates many experiments made in order to obtain Auorine in a separate state, but none of them were attended with success. As chlorine has the property of decomposing several oxides, and driving off their oxygen, it occurred to him as likely that it might in certain cases drive off fluorine. Fluate of silver and fluate of mercury, with this view, were acted upon by chlorine. The fluoric acid (or fluorine) was disengaged, and horn silver and corrosive sublimate formed; but no fluorine was

set free. When the experiments were made in glass retorts, the glass was corroded, and silicated fluoric acid gas obtained. When they were made in platinum vessels, the metal was corroded, and a red or brown powder formed. It would seem from the trials made that fluorine has so violent an action on all other bodies that it is very difficult, if not impossible to obtain it in a sepa rate state. The author promises to continue this subject in a subsequent paper. 1929

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5. A paper by Mr. Alman on the method of freeing equations from surds, though the roots be pretty high in their dimensions. From the nature of this paper it could not be read at full length, so that it is not possible to give any idea of the method employed by the author; but he referred to a method previously given in the Irish Transactions by Mr. Money, which the con siders as general, and which probably constitutes the foundation of his own.

• The Society adjourned till the 4th of November next.

On the 2d of April part of a paper by Mr. John Farey, sen. off the Ashover denudation in the county of Derby was read. This part of the paper is not susceptible of abridgment.

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On the 23d of April a notice by the Rev. J. J. Conybeare, relative to the state of Tintagel, in Cornwall, was read. This slate would appear to be transition slate. It answers well for roofing slate, and is traversed by veins containing quartz, calca reous spar, chlorite, and adularia.

Mr. Farey's paper on the Ashover denudation was concluded. The structure of Derbyshire, according to Mr. Farey, consists of alternate formations of limestone and toadstone, in the folbowing order, beginning with the lowest :

On the 7th of May part of a paper, by Dr. Macculloch, on the geology of certain parts of Scotland, was read. The prin cipal and fundamental rock of the island of Jura is a rock called. by some granular quartz, by others granite, and by all considered as a primitive rock; but Dr. Macculloch considers it as a mechanical deposite of quartz and felspar, formed from the older

rocks, and therefore not entitled to the name of primitive. According to Professor Jameson, this rock rises from below the mica slate. Hence it follows according to Dr. Macculloch, either that the mica slate is not primitive, or that the primitive are not the oldest rocks. 289 9401 19isregar

Rona consists chiefly of rocks of gneiss and hornblende. The gneiss is traversed by numerous veins of graphic granite.

The district of Assynt, forming the western part of Sutherland, contains mountains composed of the same granular quartz as occurs in Jura, and therefore, according to Dr. Macculloch, a mechanical deposite Associated with this rock, occur compact gneiss, hornblende slate, and sienitic granite. There occurs also a great deposite of limestone, which appears to alternate with the same rock. It is in two very thick beds, with the granular quartz interposed. This limestone is dark grey, or nearly black, of an earthy aspect, and minute granular texture, and smells offensive when rubbed.. 971 29 w

On the 21st of May the rest of Dr. Macculloch's paper on the geology of different parts of Scotland was concluded. The granular quartz of Isla, according to Dr. Macculloch, is a mechanical deposite like that of Jura. It alternates with mica slate and clay slate, and with a very important formation of limestone. N

Schehallien, according to Dr. Macculloch, consists of a central ridge of granular quartz, which he considers as a sandstone, flanked on every side by beds of mica slate nearly vertical, and containing subordinate beds of limestone.

The vicinity of Crinan is remarkable for containing nearly vertical beds of grey-wacke and grey-wacke slate.

The rocks bounding the valley of Aberfoyle towards Ben Ledi consist of alternations of grey-wacke and grey-wacke slate, with clay slate; then comes a fine roofing slate, approaching in parts to mica slate, but consisting of grains cemented by mica slate. Beyond this, mica slate makes its appearance.

A paper by the Rev. William Gregor was also read, containing observations on a species of tremolite found in Cornwall. It occurs in a dark green serpentine rock forming the ridge called Clickertor, in the neighbourhood of Liskeard. It was composed of