A paper, entitled Some Observations on the Salt Mines of Cardina made during a Tour in Spain in the Summer of 1814, by Dr. Traill, was read. From the bank of the river Cardonero, near the town of Cardona, in the province of Catalonia, a small valley extends for about half a mile in a direction from E. S. E. to W. N. W., bounded by steep and lofty ridges, of a coarse yellowish grey micaceous sand-stone. The bottom and immediate sides of the valley consist of reddish-brown clay, from which large imbedded masses of rock salt project in the manner of more ordinary rocks. At the upper extremity of the valley is a rugged precipice from 400 to 500 feet in height, of greyish-white salt, being perhaps partly natural, but principally artificial, as it forms the side of the great quarry from which this valuable mineral has been extracted during many ages. The lowest part of the present works has a solid floor of pure salt, and is nearly on a level with the bottom of the valley, where no salt occurs, but the real depth of the bed has not been ascertained. The surface of the precipice of salt, which has been long exposed to the weather, is furrowed by innumerable shallow tortuous channels, divided from each other by their edges, often so sharp as to cut the hands like broken glass. This appearance is evidently produced by the winter rains, which in their descent along the face of the rock become nearly saturated with the salt which they dissolve. The general colour of the exposed surface is greyish white, tinged here and there of a pale reddish brown by the intermixture of clay. Towards the extremities of the rock extremely thin layers of plastic clay are insinuated between layers of salt, giving the mass a waved and striped appearance. The fracture of the salt is highly crystalline, and usually exhibits large grained distinct concretions. A brine spring flows out at the foot of the great precipice, the water of which is probably almost saturated, since the channel which it has worn in the salt, over which it has flowed for many years, is not more than two feet wide, and less than a foot in depth. No specimens were observed by Dr. T. of the fibrous variety of salt, nor was there the least appearance of gypsum in the neighbourhood. The salt is quarried by wedges and pickaxes, and when ground in a common mill is perfectly white and fit for

use.

Dec. 15.-The reading of Dr. Berger's paper on the Physical Geography of the County of Donegal, in Ireland, which had occupied the Society during the two preceding meetings, was concluded.

The county of Donegal presents an area of about 2,000 square miles, of very varied surface. By far the greater part of this is occupied by primitive rocks, which, rising to considerable elevations above the level of the sea, constitute a very distinct chain of mountains, about 54 miles in extreme length from N. E. to S. W. This chain is itself composed of six nearly parallel and equidistant lines, the entire breadth of which may be stated on an average at about 15 miles. The northernmost parallel, ranging about three miles from the coast, extends from Sheephaven to the Bay of

Giddore. It is composed of several mountainous elevations, more or less connected together; some of which are round backed, do not exceed 800 feet in height, and consist of green-stone; while the others have long flat summits subsiding to the S. W., attain in some parts an elevation of 1,200 feet, are excessively barren, and consist of quartz rock. Of these latter the most remarkable is Caintrena mountain.

The second parallel runs about three miles south of the first, including most of the highest mountains of the county, and is almost wholly composed of quartz rock. It forms a continuous line from Muckish to Arigie, of which the principal summits are Muckish mountain, 2,100 feet high, and exhibiting on its south-western side a wall of quartz rock nearly 1,400 feet high; the three mountains called Aghla, the highest of which rises about 1,900 feet above the sea; and Arigie, the loftiest in the county, being at least 2,400 feet in height.

The third parallel lies at the distance of two or three miles south of the second, and consists entirely of gneiss. It presents roundbacked hills more fertile than the quartz rock mountains, and for the most part of inferior elevation. The two mountains, however, of the name of Slieve-Snaght, which belong to this range, must be considered as exceptions with regard to the last particular, as the lower of them is nearly 1,900, and the higher exceeds 2,100, feet in height.

The fourth parallel, almost adjacent to the third, is, like that, composed entirely of gneiss. It is of inferior elevation, the loftiest summit not exceeding 1,700 feet. In parts it is covered by bog; but, upon the whole, offers a large extent of good pasturage.

The fifth parallel is the longest, but the most interrupted, of any. It commences with Binnion Hill, in Innishaven, and extends as far as the entrance of Lough Sivilly. The whole of this range is quartz rock; the summits vary in height from 800 to 1,700 feet, the latter of which is the elevation of Aghla-more, the principal mountain of the line.

The sixth parallel consists of groups loosely connected with each other, some of which (and those the highest) consist of quartz rock. Of these latter Dooghrsey, 2,195 feet above the sea, is the most remarkable.

The spaces which separate the above-mentioned lines of mountain from each other form longitudinal vallies, the course of which nearly corresponds with the bearing or dead level of the strata. From each opening of the valley the ground rises more or less rapidly, but in an unequal proportion, till it attains the summit level in which various springs originate, the waters of which run N. E. and S. W., and are augmented in their progress by the streams discharged into them from the transverse valleys, by which latter the continuity of the main ridges is more or less interrupted. The summit level of the valley between the first and second lines of mountains is 347 feet above the level of the sea; of that between

the second and third lines, 940 feet; the elevation of the others was not ascertained. The mean elevation of the flats and valleys, and champaign land of the county, is about 240 feet.

Most of the individual mountains, and the chains themselves, generally speaking, have a greater declivity to the S. than to the N.; but this declivity is more rapid on the N. than on the S., amounting in the former to eight, and in the latter to only two, feet in 100. The slopes to the N. are encumbered, and rendered uneven, by fallen blocks and bowlders, while those to the S. are quite smooth and even.

A letter from the Rev. Archdeacon Barnes to Mr. Buckland, dated Bombay, March 31, 1815, was read.

In this letter Mr. Barnes communicates, on the authority of Mr. Copland, Assistant Surgeon to the European forces in the Guzerat, some particulars relative to the carnelians of Cambay.

These are all procured from the neighbourhood of Broach, by sinking pits during the dry season in the channels of torrents. The nodules which are thus found lie intermixed with other rolled pebbles, and weigh from a few ounces to two or three pounds. Their colour, when recent, is blackish olive, passing into grey. The preparation which they undergo is, first, exposure to the sun for several weeks, and then calcination. The latter process is performed by packing the stones in earthen pots, and covering them with a layer five or six inches thick of dried goat's dung. Fire is then applied to the mass; and in 12 hours time the pots are sufficiently cool to be removed. The stones which they contain are now examined, and are found to be some of them red, others pink, and others nearly colourless; the difference in their respective tints depending in part on the original quantity of colouring matter, and in part perhaps on the difference in the heat to which they have been exposed.

ROYAL INSTITUTE OF FRANCE.

Account of the Labours of the Class of Mathematical and Physical Sciences of the Royal Institute of France during the Year 1814,

MATHEMATICAL PART.

By M. le Chevalier Delambre, Perpetual Secretary.

(Continued from vol. vi. p. 463.)

M. Mongez, Member of the Class of Ancient History and Literature, has presented to that of the Sciences an antique piece of armour found on the banks of the Somme, and which is formed of a flint fixed in a handle of hart's-horn.

M. Barbie du Bocage, Member of the same Class, has read a memoir of M. le Comte Andreossi on the bosphorus of Thrace, in which there is a long discussion about the actual state of the shore, which ought to furnish important information to judge of the

different systems proposed by philosophers respecting the ancient state of the different seas which at present compose the Mediterranean. This is all that it is possible to say at present of a work merely known to us by a single reading.

M. Rochon, who has supplied astronomers with a more exact method of estimating the diameters of the little planets, has stated to the Class his ideas about extending that method to the diameters of the sun and moon.

M. le Chevalier Delambre has given the description of a sun-dial found at Delos among the ruins of the temple of Apollo, which was brought to Paris by M. Mauduit, jun. architect in the service of the Emperor of Russia, and deposited in the Cabinet of Antiquities. The author of the memoir has taken occasion to treat of the gnomonics of the ancients.

Just when this article was going to press, we were informed that the Antiquities of Athens by Stuart, newly translated into French, Paris, Firmin Didot, 1808, contains a gnomonic monument much more important, more curious, and especially more complete. We have read in the dissertation of Martini, p. 60, that Leroi in his Ruins of the Monuments of Ancient Greece, p. 15, has described a dial which he had seen at Athens, near the house of Thrasillus. Martini adds, that his dial is quite similar to that of Berosus. He says, likewise, that the figure which Leroi has given of it is very incomplete. This prevented us from consulting Leroi, and led us to conclude that Athens offered nothing of this kind worthy of exciting our curiosity. By the advice of M. Visconti, we have consulted the work of Stuart. We there find a very detailed description of a monument known by the name of the Tower of the Winds. It is a regular octagon, on the faces of which are represented the eight principal winds, below which are seen eight different dials, four regular and four declining, at angles of 45°, 135°, 225°, and 315°. The regular dials are the verticals of south, north, east, west; the four others are in the intermediate positions.

Vitruvius, who has described this Tower of the Winds in the sixth chapter of his first book, does not say a word about these eight dials and, what is singular is, that in the part of his book in which he speaks of all the known dials, he keeps the same silence with respect to the eight dials of Athens, though more important in every respect than those of which he names the inventors. One seems entitled to conclude from this, that the dials have been added afterwards at a time posterior to Vitruvius, and especially posterior to the time of Andronicus Cyrrhestes, author of the monument.

Stuart, who makes himself this objection, endeavours to answer it by a passage of Varro, who, speaking of this tower, denotes it by the name of the Tower of the Clock. This answer, which is far from direct, becomes still less so by the efforts which Stuart makes

to show that the tower contained a water-clock, the vestiges of which still exist in conduits, which he has described with care, and of which he has given figures in two of his plates.

If the tower contained a clepsydra, Varro might call it Tower of the Clock. He would have named it Tower of the Clock, if, besides this clepsydra, it had presented eight other clocks, or solar dial plates.

This curious particularity for the history of gnomonics was a thing sufficiently remarkable for Varro and Vitruvius. We draw little more information from the incomplete expression of the one than from the silence of the other.

The authors of the Historical Dictionary, in speaking of the architect Andronicus, say nothing of the time when he lived. Those of the Universal Biography say that "we judge from the style of architecture of that monument' already corrupted, and by the mediocrity of the bas reliefs, that he was after the time of Pericles."

In the time of Pericles and Anaxagoras the science of gnomonics was too little advanced in Greece to enable them to form these eight dials at Athens. Historians speak of the first gnomon established by Anaximander at Lacedemon. There was a great distance between this gnomon, which probably only pointed out mid-day, and the dials declining in various figures, exhibited in the Tower of the Winds. It appears, then, very probable, that Andronicus, or the author of the eight dials, whoever he was, lived a good while after Pericles, who died 429 years before our era. Nothing prevents us from supposing him contemporary with Hipparchus; and then the sun-dials at Athens will suppose nothing that was not known by the works of the ancient mathematicians, of whom Ptolemy has explained and completed the doctrine in his book of Analemma. If there be no contrary proof, I should be inclined to assign as the date the first years of our era. Probably the question will never be resolved. What is certain, or at least very probable, is that these sundials suppose a knowledge of gnomonics, and consequently of trigonometry, unless we suppose them to have been traced empyrically by means of the concave hemisphere of Berosus.

These sun-dials are of a form similar to those which we find in the Commentary of Commandin on the Analemma. Their theory is perfectly known. It remained to be known with what precision they had been drawn.

The style is every where wanting. We see only in the marble the holes where it was inserted; but the summit of the style was seldom in the axis of these holes, not even in the regular dials, which are here to the number of four. But the height of the style, and the place of its foot, are not indispensable data; we can deduce them from some of the dimensions of the dial. The author has taken care to mark on his plates the length of a considerable number of these lines; but the choice which he has made is not