small for measurement with his great heliometer at Königsberg"; Arago from Paris observations extending over 36 years (from 1811 to 1847) deduced. Hind considers that, and Main that is not very far from the truth. Kaiser's confirms Schröter. 39 Mars exhibits phases, but not to the same extent as the inferior planets. In Opposition it is perfectly circular; between this and the quadratures it is gibbous; and at the minimun phase, which occurs at the quadratures, the planet resembles the Moon 3d from the full. The character of these phases is a sufficient proof that Mars shines by the reflected light of the Sun. The phases of Mars were discovered by Galileo, who on Dec. 30, 1610 wrote to Castelli, "I dare not affirm that I can observe the phases of Mars; however, if I mistake not, I think I already perceive that he is not perfectly round." After Conjunction, when Mars first emerges from the Sun's rays, it rises some minutes before the Sun, and has a direct or Easterly motion; but since this motion is only half that of the Earth in the same direction, Mars appears to recede from the Sun in a Westerly direction, notwithstanding that its real motion among the stars is towards the East. This continues for nearly a year, and ceases when its angular distance from the Sun amounts to about 137°; then for a few days it appears stationary. After that, its motion becomes retrograde, or Westerly among the stars, and continues so until the planet is 180° distant from the Sun, or in Opposition, and consequently on the meridian at midnight. At this period its retrograde motion is swiftest; it afterwards becomes slower, and ceases altogether when the planet is again at a distance of about 137° on the other side of the Sun. Its motion then again becomes direct, and continues so, till once more the planet is lost in the solar rays, when the phenomena are renewed, but with a considerable difference in the extent and duration of the movements. The retrogradation commences or finishes when the planet is at a distance from the Sun which varies from 128° 44′ See his memoir in Ast. Nach., vol. xxxv. p. 351. Dec. 17, 1852. to 146° 37', the arc described being from 10° 6′ to 19° 35′; the duration of the retrograde motion in the former case is 6od 18h, and in the latter 8od 15h. The period in which all these changes take place, or the interval between 2 Conjunctions and 2 Oppositions, constitutes the synodical period, which amounts to 780d. Mars and the Earth come nearly to the same relative position every 32; but several centuries elapse before precise coincidence occurs o. Mars when in Opposition is a very conspicuous object in the heavens, shining with a fiery red light, which from its striking character has led to the planet being celebrated throughout the historic period. It received from the Jews on this account an epithet equivalent to "blazing," and the Greek one (Tuρóes) bears much the same meaning. Its name or epithet in many other languages is substantially the saine. Its synodic period being 780 days, it comes to Opposition and therefore attains its (general) maximum brilliancy, once in rather more than 25. When in perihelion and in perigee at the same time, which occurs once in 7 synodical revolutions (14 11m), Mars shines with a brilliancy rivalling that of Jupiter. In August 1719, the planet being only 24° from perihelion, its brightness was such as to cause a panic. The most favourable Oppositions are those which occur on or about August 26; and the least favourable those which occur about Feb. 22. Favourable Oppositions will occur in 1892 and 1909. With suitable optical assistance, Mars is found to be covered with dusky patches, which have been supposed, and with good reason, to be continents analogous to those of our own globe : these are of a dull red blue; other portions, of a greenish hue, are believed to be tracts of water. The ruddy colour, which, overpowering the green, gives the tone to the whole of the planet, was believed by Sir J. Herschel to be due to "an ochrey tinge in the general soil, like what the red sandstone districts on the Earth may possibly offer to the inhabitants of Mars, only C Smyth, Cycle of Celest. Objects, vol. i. pp. 151-2,-abridged and corrected. De Zach, Corr. Astronomique, vol. ii. p. 293. March 1819. more decided." In a telescope Mars appears less red than to the naked eye, and according to Arago the higher the power the less the intensity of the colour. Webb writes:-"The disc, when well seen, is usually mapped out in a way which gives at once the impression of land and water, the outlines, under the most favourable circumstances, being extremely sharp: the bright part is orange,-according to Secchi, sometimes dotted with red, brown, and greenish points; sometimes found by Schiaparelli filled with a complete network of their lines and minute interspaces; the darker regions, which vary greatly in depth of tone, are in places brownish, but more generally of a dull grey-green (or, according to Secchi, bluish tint), possessing the aspect of a fluid absorbent of the solar rays. If so, the proportion of land to water is considerably greater on Mars than on the Earth; so that the habitable area may possibly be Month. Not., xvi. p. 205. June 1856. e Outlines of Ast., p. 339. Pop. Ast., vol. ii. p. 483. Eng. ed. much more alike than the diameter of the planets. The water however (if such it be) is everywhere in communication, and long narrow straits are more common than on the Earth"." In 1877, when Mars was in a part of its orbit favourable for observation, Schiaparelli at Milan detected a number of minute dusky bands, for the most part very narrow and straight, traversing and cutting up the supposed continents in various directions. These markings are commonly spoken of as "Canals." They were seen again in 1879 and in 1882, in the latter year considerably more numerous and exhibiting a much more complex network. Though these markings have been seen by other observers it cannot be said that their existence in the sharply defined forms suggested by Schiaparelli is generally recognisable. The details of this planet are not readily seen with an instrument of small aperture, yet there are several features which are well within the powers of a 4-inch refractor or 6-inch reflector. The general tone of the disc is a reddish orange, and on it there may be seen certain gray markings, the most important of these being the "Kaiser Sea" in longitude 285°, sometimes called the "V" mark, from its resemblance to that letter. It commences above the equator on the Southern side, and extends half way to the N. pole. The Kaiser Sea is connected with two dark forms in the direction of the equator, that to the E. being called "Herschel II." Strait, and that on the W. Flammarion Sea. This large dark form cannot be mistaken, and if a telescope will show anything on the planet it will show this. It should be observed that the apparent form of the Kaiser Sea differs greatly at different oppositions of Mars, in consequence of the varying view we have of the poles. When the S. pole is towards the Earth, Kaiser Sea is considerably foreshortened; whereas when the N. pole is towards the Earth, it is elongated. Herschel II. Strait extends on the E. to the equator, where it terminates in a well-known mark, the a of Beer and Mädler, from h Celest. Objects, 4th ed. p. 141. |