presented an opportunity of again com- | paring the bases of Melun and Perpignan. In the long reticulation of triangles which separates these bases, some are favourably disposed, and were advantageously substituted, in the line between the forest of St. Croix and Bourges, for those of the meridian of Dunkirk. Now, this new comparison, so far from confirming the well-known and, probably, accidental agreement of these two bases, did on the contrary, exhibit a very great discrepancy; for the base of Perpignan calculated from that of Melun differed 1m 82, (about 5.8 English feet,) from the actual admeasurement. 296 This unexpected difference, which, there is now no reason to doubt, produced a necessity of correcting the length of the arc of the meridian obtained by Delambre, and which was employed concurrently with that of the equator in the calculation of the length of the Metre, seeing that this unit was definitively settled to be 3 feet 11 lines of the ancient iron toise of the academy taken at 13 of the thermometer of Réaumur. M. Puissant then showed, that the true length of the arc of the meridian, which extends from the parallel of Greenwich to that of Formentera, exceeds by 90-2 toises, the length given by Delambre. Consequently, the metre ought to be lengthened the of a line, or about the sixth of a millimetret, in order to be precisely, as was intended, the ten millionth part of the distance from the equator to the pole. As M M. Arago and Biot had been two of the commission for the continuation of the project, they naturally felt that the result announced by M. Puissant appeared to call the correctness of their splendid work into question. To meet the suspicion, the two academicians pointed out to their colleague that the result published by the commission had been obtained by three calculators unknown to each other, and according to a method, which necessarily introducing different combinations, as necessarily gave additional confidence on the results. At a subsequent sitting, when M. Puissant, in proceeding, stated that he now, by a mode of calculation peculiar to himself, found that an increase of 57 toises was necessary in that part of the meridional arc which crossed the triangulation of the astronomers of the commission, it was asked by M M. Arago and Biot, "whether the error lay on the side of the three calcu lators, or did it result from the new formula? If it could be possible that each of these three calculators could have made each separately an error of the same quantity, was it not also possible that this newly-introduced formula might not be quite exact? And," say M M. Arago and Biot, "as the works relative to the determination of the metre are not even yet entirely published, nor definitively settled, we shall again undertake this subject, and then we will scrupulously examine the methods employed in the calcution of our triangles, and on whichever side shall fall the error of the actual computations, we shall not hesitate to point it out." M. Puissant, by no means disposed to accept this promise of future correction, continued to agitate the question with his scientific colleagues, and after having gone through the calculations by two different methods, and by means of tables of geodæsical measures, his first conclusion was confirmed; and he asserted that there was an error of 57 toises, (about 1214 English yards,) which affected the true meridional distance as calculated by the Bureau des Longitudes, between Montjouy, and Formentera,-"an error," said M. Puissant, "which it is important to the interests of science to correct, and which can only be explained by supposing some mistake between the two stations at Morella, which are a very small distance from each other, and were required to connect Montjouy with the general triangulation.' Subsequent investigations, made by the indefatigable M. Puissant, into every part of his previous labour, and lations were founded, and additional into every document on which his calcurepetitions of his calculations, not only established the reality of the error, and of its amount, but also enabled him to point out the actual position of the place where it occurred. He ascertained that it ought not to be attributed to Delambre nor to any of the scientific successors to him, in that part of the arc measured by them, but that it proceeded from the circumstance, that the station of the second order, fixed by Méchain at Sierra Morella, has, inadvertently, been taken for that which he had used, at the same place, to form the triangle Matas-Montjouy-Sierra-Morella, (the first of the Table, p. 179, Vol. IV., of La Base du Système Métrique.) M. Puissant has, in consequence, assigned to the arc in question a length of 153662 75 toises, and not that of 153605 2, given to it by MM. Bouvard, Mathieu, and Burckhard. Though it is to be lamented that an error, of the smallest possible account, should have occurred in so important a work, yet it will not be without some good effects; it will establish the necessity of the increasing vigilance and uncompromising rigour, so ably urged by M. Dupin, in his Discourse before the Academy*, as imperiously demanded in all such operations; and, piqued as the surviving members of the commission must be, it will enlist all the personal feelings and gigantic acquirements on the side of further investigation, so that, eventually, the length of the metre will be determined to the greatest possible minuteness, and without any chance of future correction ever being found to be necessary. The method, by the aid of which M. Puissant has determined the length of an arc of the meridian, is based upon the most indisputable principles, and the various applications he has made of it have demonstrated its simplicity and correctness. In using it for the purpose referred to, he ascertained that the depression of the terrestrial spheroid, generally taken at, is only, an amount precisely the same as that deduced from the lunar inequalities. Blissful Ignorance. THE ladies of North Britain and others, admirers of the beetle-stone, and who frequently select it from their trinketbox, and place it in a conspicuous situation on the person, in the shape of a brooch, &c., will hardly thank their facetious friend, Dr. Buckland, for the following account of the origin of the jewel: * See page 257 of this Volume. "In 1832, Mr. W. O. Trevelyan recognised coprolites in the centre of the nodules of clay-ironstone, that abound in a low cliff composed of strata belonging to the coal-formation at Newhaven, near Leith. I visited the spot with this gentleman and Lord Greenock, in September, 1834, and found these nodules strewed so thickly upon the shore, that a few minutes sufficed to collect more specimens than I could carry; many of these contained a fossil fish, or fragment of a plant, but the greater number had for their nucleus a coprolite, exhibiting an internal spiral structure; they were probably derived from voracious fishes, whose bones are found in the same stratum, These nodules take a beautiful polish, and have been applied by the lapidaries of Edinburgh to make tables, letter-pressers, and ladies' ornaments, under the name of beetle-stones, from their supposed insect origin." In spite of their polish and their beauty, beetle-stones will now, we fear, be irrevocably banished from the toilet and the writing-table. Alas! "Where ignorance is bliss, Cold fatal to Barbel. M. AGASSIZ has observed that a sudden depression to the amount of 15°, of the temperature of the water in the Glat, which falls into the lake of Zurich, caused the immediate death of thousands of barbel. First Belgian Scientific Congress. THE first national association of scientific and learned men, in Belgium, met at Liège, on the first of August last. About 130 members had entered their names at the commencement of the session; among them were those of two ladies, one a botanist, the other a poetess. M. Caumont, of Caen, the founder of + Fæcal remains, in a state of petrifaction, dispersed through the same strata in which the skeletons of some fossil animals are buried. The state of preservation of these very curious petrified bodies is often so perfect as to indicate not only the food of the animals from which they were derived, but also the dimensions, form, and structure of their stomach and intestinal canal. (See Trans. Geol. Society, London, 1829.) BUCKLAND, Bridgewater Treatise, 1836. the scientific congresses of France, was elected president. The business of the congress was, as in other similar national associations, divided into sections; but the subjects of inquiry were of far greater variety than in the German or the British meetings. At Liège there were added to the list, legislation, social economy, agriculture, manufactures, commerce, history, archæology, philology, and literature. Another distinct feature of the Belgian congress was, the preparation of questions on points considered the most desirable to be elucidated. These amounted to about 80: they were printed in a programme, and distributed. At the general meetings they were proposed seriatim, and several of them gave rise to discussions of great interest, and pregnant with the most valuable information. When it is stated these discussions did not prevent papers, of great interest, being read at the general assemblies, it will puzzle the visiters of the Bristol session of the British Association, to imagine how so much business could be accomplished. It may liam Allen, delivered an address on the abolition of the slave-trade, and on the complete emancipation of the negroes. The second Belgian congress is to be held at Ghent, in September, 1837. Bug-destroying made easy. M. FOURNEL, after having in vain Application of Science to Navigation French Prize-question. be useful that they should know that the Belgian philosophers met in section at six o'clock in the morning, and DURING the time that the Baron C. worked till two. They then rested and Dupin held the office of Minister of the refreshed, and, at four in the afternoon, Marine, in the government of France, met in general assembly. If we sup- he induced the king to offer a reward of pose, as we reasonably may, from the 6000 francs (2401.) for "The work or business done, that the Bureaux were memoir, in which the application of the attentive, the chairmen exact to the mathematical sciences to the art of naappointed hour, and the members punc-vigation shall be carried to the farthest tual, what a contrast shall we have to extent. the blank days, the late hours*, the empty committee-rooms, and the vacant chairs, which were so frequently complained of at Bristol! One very remarkable circumstance occurred, and, it is said, commanded the deepest attention of the congress: a Miss Anna Knight†, niece of Mr. Wil The sectional committees at Bristol rarely met before half-past ten, and it was seldom that a section was in actual operation till eleven, frequently much later, and, except in one or two of them, "school was up" often before three. This, with "halfday holidays," on Tuesday, Thursday, and Saturday, made a most serious waste of time. + We should think this is, perhaps, an error, and that it was the ci-devant Miss Frances Wright (now married to a French gentleman, and resident at Paris), the lady who made such heroic efforts in this cause in the United States, that addressed the congress. The term prescribed for the receipt of the competing works expires in the ensuing month. The decision on their merits is to be made by the Bureau des Longitudes. New Theodolite for surveying under ground. M. COMBES, professor at the Ecole des Mines, has supplied a deficiency felt by mining engineers, of an instrument for subterranean surveying; it is an adaptation to this express purpose of Gambey's theodolite, which was constructed for the French national geodesic operations. The minutiae of the construction of M. Combes's Subterranean Theodolite, as he has termed it, would not be intelligible without a figure; and we notice the improvement merely to apprize our countrymen of its existence. Recent Account of the African Desert to west, necessarily lay bare the eastern Sahara. THE extent, nature, formation, and encroachments of this mighty desert have lately been more accurately defined than heretofore by Ritter, in his Géographie Comparée. It is bounded on the north by the Biledulgerid (the Country of Dates); to the east it reaches the Atlantic; towards the south it stretches, very uniformly, to the Senegal and the Niger, with which rivers it extends between the 16° and 18° of north latitude, into the unknown regions of eastern Soudan. In magnitude, the Sahara may be compared to the half of Europe, or still more definitely to about double the Mediterranean; the area of the desert being 72,000 geographical square miles, including the Oases, and to 50,000 square miles without them: its length is 450, and its width 300 geographical miles. The essential characteristic of this desert consists in its uniformity both of surface and substance; the dead level of the former is only varied by comparatively slight elevations and depressions, -a feature which precludes the accumulation of large bodies of water, while the latter, generally speaking, is a mass of pebbles, or salt, equally distributed. The limestone, which rises into the elevations in the neighbourhood of Fezzan, and in the Haroush, is, according to Humboldt, of a formation analogous to that of the Jura: in Darfour it occasionally encloses granite, talc, and basalt. The rocks are covered over with pebbles, shingle, and with moving sand, which the wind raises in clouds like to a fine fog. The sand of the Libyan desert is composed of transparent fragments of quartz, about the third of a line in diameter; with this the surface of the subjacent rock is equally covered over in a manner analogous to that with which snow would be deposited. The eastern portion of this vast desert is much freer from sand than the western; it is intersected by low rocky shelves, denuded of sand, and quite barren, and it contains a great number of oases. The western part, on the contrary, is nearly destitute of the latter; and the few that are met with are very limited in extent. The terrific hurricanes, which about the period of the equinoxes, annually sweep over this sandy ocean, being directed from east portion. Hence arises that great quantity of rolled pebbles, of naked rocks, and of denuded oases, which are found in the Sahara, or eastern district; while the moving sands of the western one, (the Sahel) advance gradually towards the ocean, and are formed on its shores into sandy downs by the effect of the great rotatory movement of the Atlantic Ocean. Excellent springs, wells, marshes and lakes, are met with in the Sahara, on the sides of the ranges of rocks, especially in Winter: but all these advantages disappear in the Sahel, where nature presents no variety. Rivers, springs, oases, wells, and saline lakes, are there nearly unknown. Nothing is seen but indurated rock-salt, and moving sand: water is only to be met with by digging to an enormous depth, even where the process is at all practicable; while the few wells which are dispersed over the interior, are so deep that the caravans can derive no advantage from them. To prevent their being choked with sand, the wells which have been successfully established are walled round with bones of camels for want of stones, and covered over with skins: the skill with which the conductors of caravans trace their way in these monotonous solitudes to these wells when once known, is admirable. The prevailing winds in the Libyan desert are from the north and northeast; the consequence is that hills of sand are continually advancing from those quarters, at the usual rate of ten or twelve feet, as has been estimated by the gradual disappearance of springs and wells: these winds only raise into the air the fine sand;-the pebbles and shingle remain bare. The moving desert consequently covers with its sands those spaces which it has gained, while the wind from the district of moving sands converts it into a plain of gravel, pebbles, and shingle. The portion designated as Sahel, thus forming the advance guard of the Sahara, in time becomes converted into the latter; but this phenomenon is not general in Libya. The progressive advance of the sand does not then leave behind it, as might be expected, vast naked plains, because the Mediterranean is ceaselessly throwing up considerable masses of sand on its shores, these the winds seize hold of, and carry towards the interior of the con tinent: this process may be detected by the gradual disappearance of the palmtrees under the sand along the coast. The sea has even, in many places, enabled the Libyan desert to extend its domain at the expense of the valley of the Nile. This encroachment is especially remarkable near to the village of Warden, at the northern extremity of the plain of Gizeh. A belief in this encroachment of the sands is general among the Arabs, who possess accurate knowledge of all the phenomena of the desert. The well-known colossal sphinx which is now half buried by the sand, appears to them a talisman, incessantly conjuring the storm of sand not to advance further. Caviglia, who undertook to excavate the hillocks of sand accumulated at its base, discovered many remarkable objects which the desert had ingulfed. The same effects from the sand are perceivable in Nubia, whereof the numerous sphinxes, forming the avenue leading to the propylæum of the temple of Sibhoi, six alone are now visible: all the others, together with the greater part of this superb temple, being overwhelmed by sand. Huttonian Theory of Rain Controverted. THE most plausible Theory of Rain ever given to the world, is that of Dr. Hutton. He supposes two currents of air of different temperatures, both nearly saturated with vapour, to be mingled together, and that a precipitation of course takes place, in accordance with the known fact, that at their mean temperature all their vapour cannot be retained, and therefore the surplus will be precipitated. This theory is defective in two respects: First, it does not show how two currents of air could be mingled to any considerable extent; and second, it does not show by calculation, that rain to any considerable amount would be produced, even if large masses of air, at very different temperatures, should be mingled together, which it would be easy to show never can happen, especially in the torrid zone. It may fairly be presumed that no advocate of the Huttorian theory would suppose that more than five hundred feet of a stratum of cold air could be mingled with a stratum of warm air, five hundred feet of perpendicular height. Now it will An account of a recent personal visit be found by calculation, that if one of to the Sahara is about to issue from the these strata is at 60°, and the other at French press at Algiers. M. Baudoin, 40°, and both saturated previous to their a native of Provence, being at Algiers mixture, the whole amount of precipitasoon after the taking of the city by the tion, provided they took the mean temFrench, was surprised, as he was walk-perature of 50°, would be less than a ing in the environs, by a party of Arabs of the Issers tribe, and carried off by them into their own territory; there they circumcised and sold him to a Mahometan priest. A long series of travels and singular adventures followed this event, and with his master he reached the Sahara. During his journey, he describes having seen some wealthy cities and interesting ruins; among the latter he saw inscriptions, whose characters resembled neither the Greek, nor Latin, nor Arabic alphabets. Having obtained his liberty by the death of his master, who fell a victim to the cholera, which raged to the very centre of Africa in 1835, he immediately prepared to rejoin his compatriots, and succeeded by avoiding the direct routes. The narrative, by a competent person, of a journey made under such circumstances, would be extremely valuable, as the part of Africa said to have been visited is scarcely known to Europeans. grain and one half on each square inch of surface. But as the latent calorie evolved in the condensation of the vapour, would not suffer the mean temperature of the two strata, when mixed, to be acquired, but some temperature above 50°, therefore a less quantity than that mentioned would be precipitated. Such a quantity, in most cases, would be entirely evaporated in passing down through the air below, and never reach the earth. It was mentioned before, that 5'1 inches of rain fell in Wilmington, on the 29th of July, 1834, in two and a half hours; let us see whether such a rain could be produced at all, on the Huttonian principles, making the most extravagant allowance for the quantity of air mingled, and also for the difference of temperature of the two strata. Let us suppose, then, that one-half of the atmosphere at 80° Fahr., should be mingled with the other half at zero over the region round Wilmington, |