blished the science on a new foundation. Ptolemy continued this labour, and gave a complete treatise on this science in his Almagest. It was the general opinion of the antients, that the uniform circular motion being the most simple and natural was necessarily that of the heavenly bodies. This error maintained its ground till the time of Kepler. Ptolemy adopted it, and, supposing the earth to be the centre of the celestial motions, he endeavoured to represent their inequalities in this false hypothesis. He supposed the Sun, Moon, and Planets, in motion round the Earth, in the following order of distances,-the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn. [See Introduction to Time's Telescope, 1815.] The astronomical edifice raised by Ptolemy subsisted nearly fourteen centuries; and, now that it is destroyed, his Almagest, considered as a depository of antient observations, is one of the most precious monuments of antiquity. Ptolemy rendered very great service to geography, by collecting all the known longitudes and latitudes of different places, and laying the foundation of the method of projections for the construction of geographical charts. He composed a treatise on optics, which is lost: in this he explained the nature of astronomical refraction. He likewise wrote treatises on the several sciences of chronology, music, gnomonics, and mechanics. So many labours, and on such a variety of subjects, manifest a very superior genius, and will ever obtain for him a distinguished rank in the history of science. On the revival of astronomy, when his system gave way to that of nature, mankind avenged themselves on him, by accusing him of having appropriated to himself the discoveries of his predecessors; but, in his time,' says La Place, 'the works of Hipparchus, and of the astronomers of Alexandria, must have been sufficiently known to have rendered excusable his not distinguishing what belonged to them from his own discoveries. As to the long continuation of his errors, it must be attributed to the same causes which replunged Europe into darkness. The fame of Ptolemy has met with the same fate as that of Aristotle and Des Cartes. Their errors were no sooner recognised, than a blind admiration gave way to an unjust contempt for even science itself: the most useful revolutions are not always exempt from passion and prejudice.' [To be continued.] Astronomical Occurrences. TABLE Of Equation of Time. [See pp. 19, 20.] min. sec. Thursday 1, to the time on the dial add 13 53 ... Tuesday 6, .... Monday.. 26, The Sun enters Pisces at 54 m. past 4 in the afternoon of the 19th. TABLE Of the Time of the Sun's Rising and Setting every fifth Day. The Moon enters her first quarter at 30 m. past 1 o'clock on the 6th: she is full at 9 m. after noon on the 13th; she enters her last quarter at 42 m. after 3 in the morning on the 20th day; and it is new Moon at 30 m. past 3 in the morning of the 28th. The star in Scorpio will be eclipsed by the Moon on the 20th the immersion will be 39 m. after 3 in the morning, and its emersion at 52 m, past 4. In the former case it will be 43° south of the Moon's centre; in the latter, 44° north. Mercury will appear stationary on the 17th; on the 10th he will be at its greatest elongation; at 30 m. past 5 in the afternoon of the 26th, he will be in his inferior conjunction. Mars will be in his quadrature, with respect to the Earth and Sun, on the 3d, at 1 o'clock at noon. Saturn will be in conjunction on the 4th, at 15 m. past 3 in the afternoon. TABLE Of the Eclipses of Jupiter's first Satellite, which are visible here. Two serpses of the second satellite will be visible in the course of the month, viz. the first on the 19th, at 12 m. past 2 in the morning; and the second on the 26th, at 45 m. past 4 o'clock in the morning. We may in this, and in the Occurrences for the month of April, take the opportunity of enlarging_on the subject of satellites, and point out why those of Jupiter are only deemed important to practical purposes.. Satellites are secondary planets moving round the planets, as the Moon moves about the Earth: they have derived their name from the circumstance of their being always found attending them, and making the journey around the Sun together with them. The satellites move about their primary planets, as their centres, by the same laws as those primary ones move about their centre, the Sun. It should be observed, that the words moon and satellite are sometimes used as synonymous terms: thus we sometimes say Jupiter's moons, and sometimes Jupiter's satellites; and persons at all conversant with scientific subjects are never at a loss to know our meaning but generally we distinguish them in this way; restraining the term moon to the Earth's satellite, and satellite to the little moons more lately discovered which revolve about Jupiter, Saturn, and the Herschel planets. It has not been ascertained that there are any satellites belonging to Mercury, Venus, or Mars. The satellites of Jupiter are four secondary planets, which perform their revolutions about Jupiter as that planet performs his around the Sun. Three of these were originally discovered by Simon Marius, mathematician to the Elector of Brandenburg, about the end of November, 1609; and in the following January he saw the fourth. In the same month, Galileo observed the four satellites in Italy, and almost immediately published his observations of what he denominated the circumjovial satellites. The discovery of these satellites was, in its consequences, of great importance, as, by means of their eclipses, a ready method was afforded of finding the longitude of places on the earth; and as the eclipses of these satellites led M. Roemer to the discovery of the progressive motion of light, Dr. Bradley was then enabled to solve an apparent motion for the fixed stars, for which he could not otherwise account. may These satellites of Jupiter may generally be seen with a telescope that magnifies thirty times; but when the air is very still and clear, the third and fourth sometimes be seen with the naked eye. When viewed through a common telescope, they appear to be of different magnitudes; but their diameters are so extremely small, that an accurate measure of them cannot be obtained but by means of a micrometer. A method, however, of estimating their relative magnitude is furnished by their eclipses, the larger one taking a longer time to enter into the shadow than the smaller. Dr. Herschel thinks the third satellite is larger than the others. The first is larger than the second, and nearly the size of the fourth; and the second is a little smaller than the first and fourth, or the smallest of them all. The Naturalist's Diary. Still at times the flaky shower descends, In this cold and gloomy month, the weather in England is usually variable, but most inclined to frost and snow. The thermometer is often down below the freezing point, but is generally found at noon between 36° and 46°: towards the end of the month it sometimes rises to 50°, or even 52° or 54°. The severe weather, generally, breaks up with a sudden thaw, accompanied by wind and rain; torrents of water pour from the hills, and the snow is completely dissolved. Rivers swell and inundate the surrounding country, often carrying away bridges, cattle, mills, gates, &c., and causing great injury to the farmer. But so variable is the weather in this month, that frequently frost. again usurps the year'.' The following stanzas of our immortal bard are happily descriptive of this season: When icicles hang by the wall, And Dick the shepherd blows his nail, A merry note, While greasie Jane doth keel the pot. A merry note, While greasie Jane doth keel the pot, |