ART. X.-Abstract of Meteorological Observations, made at Mantanzas, Cuba, lat. 23° 2′ N., lon. 81° 36′ W. from Aug. 1, 1832, to July 31, 1833; by A. MALLORY. TO THE EDITOR. Sir-Annexed you have some meteorological observations, made by myself at this place during the past year, which might prove of interest to some of your numerous readers, should they be deemed worthy of a place in your valuable Journal. The observations upon the weather, were carefully made, and the thermometer, an excellent instrument of Doliand's, was placed in a situation where it communicated freely with the external air. After seeing, in your July No. of last year, a description of Mr. DeWitt's nine inch Conical Rain Gage, I sent to New York, hoping to obtain the instrument, but it was not to be found; you will therefore see that my observations are incomplete, in an important point. I remain, Sir, with high respect, your obt. servt. May, June, July, 3,9 84 16,31 84 1984 26 88 30,31 90 Mean temperature at sunrise. Mean temperature at 2 P. M. Mean temperature at sunset. Aggregate of mean temperature each month. Day. Maximum. Highest deg. of temperature. Day. Minimum. Lowest deg. of temperature. 79.25 86.50 83.00 83.00 28 1,1188 188! 5,6 84 77.00 86.30 83.00 82.00 8,15,16,17 90 76.50 85.50 82.30 81.50 12 11 20 11 13 17 3 2 23 20 64 20 16 245 1966776 North winds. 00 3 25 6 0 0 5 22 5 4 1 2 24 2 2 2 0120080 1 13 711 0 3 20 010 0 370 20 14 21 10 9 21 19 79.25 88.00 83.75 83.75 12 days. 90 27,28 76 14 13 20 10 10 0 22 08 Agg. temperature,[75.60 83.40 80.70 79.90] of From the foregoing, it will be seen that the mean temperature twelve months past, was 79° 9′, or within a fraction of 80°. The coldest month was January, 74° 7'; the warmest, June, 83° 7'. The coldest day was March 11, when the mercury fell to 58°; the warmest, 90°, at several periods in April, May, June, July and August, VOL. XXVI.-No. 1. 12 range of mercury 320, greatest range in one day 18°. In the beginning, I kept no column for variable winds. I think about twenty days should have been marked thus; the wind rarely blows an entire day from the west, but it did on the 18th of May. The south winds in the spring, are very dry, hot, and oppressive, and generally blow with considerable violence. It is a fact that the more open your house is kept during their prevalence, the higher will the mercury rise in the thermometer. 'The trades,' as will be observed, are the prevailing winds, and under their influence, the weather is never oppressive, although the mercury may be at 90°; they range from N. E. to E. We have the northers' from October until March; they are always cold, generally attended with rain in the beginning, usually last three days, and blow with considerable violence. They in fact bring the little rain we have during winter, beginning generally at S. W. they change in a couple of hours to W. N. W. & N. The rain commencing at W. ART. XI.-Physical Discovery.—(Retrospective.)—The Magnetic Needle made to indicate the true North, and rendered more steady, by a newly invented Magnetic process. Extracted and translated from the Avant-Coureur, of Monday, June 10, 1771.-No. 23; by Gen. H. A. S. DEARBORN, and by him communicated for this Journal. THE actual declination of the Magnetic Needle, from the true north, as indicated by this false guide, amounts to nearly twenty degrees, and thereby deprives the common Mariner's Compass of the general and daily advantages of that instrument, which should be in fact a portable horologe, and indicate with exactness the meridian line. The author of the new edition and translation of Pliny the Naturalist, announced in one of the last numbers of the Avant-Coureur, has devised and executed a very curious magnetic process, which represses the north west deviation of the magnet, or rather, which compells nature, in one of her most mysterious laws, to overcome a kind of impotency in the magnetic needle, which, for a century has not allowed it, in the compass, to indicate the true north. This process consists in magnetizing two needles, one of which should be, but about half the size of the other. They are proved seperately, by placing them successively on a pivot, and causing them to gyrate for some time, until it is ascertained, by various experiments, that they are magnetized, and that one end of each of them, is di rected to the north, at a certain deviation, which, for Paris and its environs, is known to be about twenty degrees. The cap of the small needle, is then taken out, which leaves a hole in its middle, and thus admits of its being placed on the cap of the large needle and pressed down to the latter. The cap therefore should not have the exterior form of common compass needles, but that of a small vertical cylinder, whose height should not exceed that of the needles generally used. The small needle is then slipped down upon this little cylinder, like a ring upon the finger, so as nearly to touch the large needle; as for reasons, which are too long here to state, it is necessary to prevent the immediate contact of the two needles; and to effect this, it is expedient to place a very thin leaf of copper between them. By this means, the two needles are suspended upon one and the same cap, but imperfectly crossed, in such a manner as to represent the cross of St. Andrew, or a pair of scissors more or less opened. When satisfied how great must be the separation, it is necessary to establish, the small needle must be secured in its position by a little sealing wax, or in any other manner, so that, as the combined needles turn upon the pivot, they be not deranged, by the air, a jar, or any other cause. As to the exact extent of the separation of the points of the needles, it is impossible to determine or adjust it, by an invariable theory, because this depends upon the size and relative magnetic powers of the two associated needles; it is therefore, necessary to ascertain, for each set of associated needles, what the extent of this separation of the needles should be, according to their relative powers, which will require an experiment of a few minutes duration. To perform this, the needles are to be arranged on the cap, more or less crossed, and the distance between their points, is to be enlarged or diminished, until it is perceived that the large needle, in moving freely, at last is directed accurately to the true north. Now this is easily accomplished, after having tried and examined, for a minute or two, various distances, until the requisite degree of separation has been discovered. It must not be forgotten, that the essential conditions of the operation require, that the two needles be crossed in such a manner, that the north point of the small needle, be directed to the left of the north point of the large one, between the west and the north, and the other one between the east and the south; for if the north point of the small needle, from the nature of the separation, cross the large needle in two opposite directions, this erroneous disposition, augments the actual deviation of the magnet, instead of rectifying it. This discovery, is not a mere speculation,—a simple project, but it is an invention that has been tested by experiments, which the author has actually made. We have had the satisfaction of seeing them made in our presence; and we, moreover, have in our cabinet, the first compass of this kind, which the author has constructed and confided to us. The explanation which he has given us, of his magnetic process, is equally curious, and satifactory. The little needle, according to his theory, endeavors as much as it is enabled, and on its own account, to approach the north like all other magnetic needles, to within about twenty degrees. It is counteracted in this direction, by the large needle, which, of right, preoccupies that position, and takes possession of it; but as the effort of the small needle cannot be inconsequential, its rival, finds itself to be pushed a little farther, this impulsion acting by reason of the quantity of inherent power in the little needle. The author cencludes that the deviation which is observable in the common compass, results from an actual defect in the magnet, that is, from a weakness in its directing power; and that it is from this defect in its power, that the common magnetic needle does not now point to the true north, as it did in 1666, whereas by associating with it, another needle, it is rendered, by this auxiliary combination, that nineteen twentieths degree of power which it wants at the present time to attain this object. Such a discovery as this cannot but excite the curiosity of all the friends of the arts; and we consider it as calculated to extend the sphere of acquired knowledge, on the character and properties of the magnet, a complete union of which, according to some philosophers, should result in a theory of longitude. At all events, we can, with reason, flatter ourselves, (thanks to the invention which we have made. public,) that the mariner's compass, is advancing towards perfection. In fact, the common magnetic needle has only one cause of direction, which is deranged by the least extraneous impulse, whereas the new needle, combined, as has been described, tends to a point, where it is fixed by two directive causes, which form an angle, and by which it is, in a manner, confined, which necessarily, renders it less unstable, less capricious, and less subject to variation. ART. XII.-On the Prairies of Alabama; by W. W. MCGUIRE, (in a letter to the Editor.*) FROM the period of the first settlement of this State to the present time, the prairies have been objects of great curiosity and have attracted much attention; still, although the field for scientific investigation is so rich and interesting, no one has, to my knowledge, attempted a minute examination of it. The striking peculiarities of soil, of geological conformation and organic productions, especially in shells and other marine substances, which are found scattered indiscriminately over the prairies, are well adapted to attract attention and to excite investigation respecting the period and causes of the formation. of the prairies and their fossils. Many who have never conceived of the possibility of any great change in the surface of the earth, except that produced by the deluge recorded in the pentateuch, attribute to that event, the present position of these shells. Others, taking a still narrower view, believe them to have been removed by the agency of man, from their native beds to the place where they are now found. My own observations, although limited, have satisfied me, that the prairies once constituted the boundary of the Atlantic Ocean. In support of this opinion there are still existing many satisfactory proofs, although ages must have elapsed since these changes took place; strong evidence also exists that this great change has been effected by the elevating power of earthquakes, volcanoes and subterranean heat. The face of the country, from the mountains to the prairies, is rough and uneven, presenting an outline differing from all other hilly or broken countries which I have yet seen. It abounds in iron pyrites, and pebbles. Beds of good iron ore, of anthracite and bituminous coal, and of limestone and sandstone, are found in several places. The country lying between the prairies and the sea coast is generally, if not altogether, of the same character as that on the coast from the Potomac to St. Mary's, viz.; level sandy plains, some fertile, some sterile, either dry or swampy and covered with pine, oak, cypress, cane, &c.; but it generally, perhaps uniformly, shows the distinctive peculiarities of the above named coast. The changes, in all places, are sudden and abrupt, changing from the peculiar soil and character of the prairies, to that of the coast, which is sterile, in some places almost pure silica; or of alluvial formations along the rivers, swamps and marshes, differing in fertility, according to the portions in which silica and vegetable matter are * Dated a year since. |