1843. April, 717-362-6 1 5169 17 4 81 4 -580 7 14 10 9 7 7 4 11 496 1842. 5626 820 133 433 20 99 123 110 110 89 137 45 36 5959-78 5 3-52 25 7.31 13-93 5-07 0 45 5 640 4 174 5 1-94 14-64 0 0 1.73 235-42 3 7 1.37 67-4 76-8 56-9 29-847-30-05029-623 39 234 92 151 110 89 75 103 31 13 41 43 52 Jan'ry, 54 66-6 33 3 29-911 30-070 29-620, 6 20 329-9112 613 4 20 5 10 9 8 54846 646 3 23 4 16 629 7 18 June, 78-983-375-3 784 876 583 0 16 14 July, 81 86-3 78-5 822 30-013 Aug'st, 79-4 33-375-3 Sept. 79-683-6 73-3 9 12 18 616 4 20 7 9 9 8 1 24-04 10 733 1 20 10 5 16 19 66 1 76-3 53-729-721 30-020 29 625 38 221 106 120 107 115 83 113 42 12 40 78-73 Mean Ifor 10 ys 66-875-7 54-4 29-792 30-021 29-595 49-7 216-8-99-1 Mean depth of rain for 6 y'rs, 54-92 REMARKS. The foregoing tables are designed to show the mean, maximum, and minimum, of the Thermometer and Barometer, the number of clear, cloudy and wet days, the prevailing winds, and depth of rain, for ten years in the city of Natchez. These tables show clearly that the climate is good, and conducive to life and health, and all other blessings that heart can desire. With the exception of occasional epidemics, far between, Natchez is as healthy a city as can be found in the same parallel of latitude around the world, proved by the multitude and healthiness of the children; and where temperance, industry and good behavior are observed by the adult citizens, they are as healthy and long lived as in any part of the United States, let that part be where it may. Extremes of heat and cold, dry and wet weather are unknown. Injurious drought and heavy rains are rare. Within the last thirteen years, there have been eight destructive fires in the city, seven of which were followed by rain more or less heavy. These facts are mentioned as probable confirmation of Professor Espy's doctrine upon the subject; but whether true or not, let every one judge for himself. Natchez, Aug. 12, 1846. 2. Variations in the climate of France; (L'Institut, No. 647.)-M. Dureau de Lamalle, in May last, read a memoir before the French Academy, in which he contested the value of the citations taken from ancient authors by M. Fuster adduced to prove that the mean temperature of France had diminished. V. ASTRONOMY. 1. Atmosphere of the Moon; (from an article on the Physical Constitution of the Moon, by Prof. E. LOOMIS, in the Sidereal Messenger, Cincinnati, i, p. 20.)-Whether we observe the moon with the naked eye or with the most powerful telescope, we have no difficulty in say ing precisely where day ceases and night begins. The shadows of the lunar mountains are dark as midnight.—The transition seems instanta. neous from midnight to noonday. We conclude that the moon has no twilight-or rather the legitimate conclusion is, that the moon has no twilight which can be appreciated by this mode of observation. More refined methods of observation have disclosed the existence of a feeble twilight. If there was no atmosphere, the line which joins the extremities of the horns of the new moon should pass exactly through the centre of the disc-that is, the ring of light should be an exact semicircle. By observing the moon when her phases were extremely falcated, Schröter discovered a faint glimmering light extending from both the cusps beyond the semicircle. The greatest breadth of this twilight was two seconds, corresponding to about two miles on the moon's surface. We admit then that the moon has a twilight, extending about two miles in breadth, from which we compute that the height of the denser part of the moon's atmosphere is 1500 feet. When the edge of the moon's disc approaches a star, the instant before its disappearance, its light must pass through the moon's atmosphere, if there be any, and suffer refraction. The light of the star, instead of moving in a straight line, must be bent behind the moon, and the star must be seen later than it would be without refraction. The contrary effect must take place at emersion; the star must re-appear sooner than it should if there were no refraction-in other words, the duration of an occultation is diminished by refraction. Now it is easy to bring this question to the test of experiment. We can compute the ance. time required by the moon to move over a space equal to its diameter, and we have but to compare with this, the time of the star's disappearThis observation has been repeated a thousand times, and the result is, that the two intervals are almost identically the same. For a long time it was considered doubtful whether there was any appreciable difference; but astronomers are now generally inclined to the opinion that there is a difference of a few seconds. This would indicate that the moon's atmosphere does refract light; but the effect is exceedingly small. The refraction produced by the earth's atmosphere is more than a thousand times greater than that of the moon. The pressure of the moon's atmosphere would be balanced by a column of mercury one forty-fifth (1) part of an inch in height. The best French air-pumps are warranted to rarefy air to one twenty-fifth (2) part of an inch of mercury. *If we use language with the utmost precision, we must say the moon has an atmosphere; but to avoid being misunderstood, we should add, that it is more rare than any we can produce with our best air-pumps. 2. On the Projection of a Star on the Dark Limb of the Moon just before its Occultation; by Prof. STEVELLY, (Rep. Brit. Assoc., 1845, p. 5.) This the Professor considered to be a result of diffraction. Sir Isaac Newton having observed the shadow of a hair placed in a strong beam of sunlight to be broader than the hair itself, was led to investigate the course of a ray as it passed by the edge of a body, like the edge of a knife placed across a hole in the window-shutter, through which a sunbeam is admitted. Beyond a certain distance the rays proceeded in their usual straight courses; at that distance they were bent towards the edge; but the courses of the nearest rays were bent away from the edge, so as to form curves convex towards it. The undulatory theory enables us to trace these curves, and they are known to be of the nature of the hyperbola, with asymptotic branches extending onwards from the diffracting edge. Prof. Stevelly conceived the dark limb of the moon to be such a diffracting edge to the slender beam of light which reached us from a fixed star; and that as the curve was, at the last moment the light was allowed to pass, convex towards the moon, the portion of the ray which last enters our eye before the star disappears, being the direction in which we should then see the star, if produced backwards, would meet the moon on her dark surface. 3. The Central Sun of the Universe.-Prof. Mädler of Dorpat has announced that he has discovered the central sun about which our sun with its attendant planets performs its circuit. His conclusions are derived from a comparison of catalogues of stars since the time of BradSECOND SERIES, Vol. II, No. 6.—Nov., 1846. 56 ley. The following summary may give some idea of the nature of his labors. 1. Of 15 stars in the group of the Pleiades, there is a great unifor mity in the proper motions, and a general decrease of declination. 2. Of 12 other stars observed by Bradley within 5° of the Pleiades, the declinations have been generally decreasing since 1755. 3. Of 35 stars observed by Bradley from 5° to 10° distant from the Pleiades, the same remark is true. 4. Of 57 stars observed by Bradley from 10 to 15° distant from the Pleiades, the declinations are generally decreasing. Out of 110 stars within 15 of the Pleiades, whose declinations are given by Bradley, we find 60 motions towards the South; 49 motions very slow and yet undetermined; 1? towards the North. Mädler explains these facts by ascribing to the solar system a motion nearly perpendicular to the ecliptic. He also remarks that the proper motions of the stars increase with their distance from the Pleiades, the greatest proper motions known (5 to 6") occurring at a distance of about 90°. Mädler therefore concludes that the Pleiades constitute the central group of the system of fixed stars which compose the Milky Way, and that Alcyone is that particular star which is most probably the true central sun. Alcyone, known also as ʼn Tauri, or 25 Tauri, is a double star of the third or fourth magnitude in A. R. 3h. 38m.; Dec. 23° 39′ N. Mädler estimates the distance of Alcyone from us to be such as light would require 537 years to traverse. The time of one revolution of the sun about Alcyone he estimates at 18 millions of years. The mass of all the bodies whose distance from the central sun is not greater than our own, he estimates at 117 million times that of our sun. Prof. Schumacher in giving place to this remarkable memoir in the Astronomische Nachrichten, intimates that he entertains some doubts respecting the conclusions-doubts which will probably be shared by many other astronomers. 4. Antares.-The announcement of the triplicity of the star Antares, at p. 280, was premature. It is probable that the appearance of the minute companion of a green color, is a result of prismatic dispersion; and that Antares is consequently a double star only. 5. The new Planet Astræa.-This newly discovered member of our system was followed at the principal European Observatories until it came too near the sun to be longer observed. The following are the |