MARS. The first of the superior planets. Its mean distance from the sun is 141.5 million miles or nearly times that of the earth; its periodic time, C86.9 days; its diameter, 4230 miles; vol ume that of the earth; density, 0.71, earth's being unity. When it is nearest to the earth (i.e. in favorable opposition) its apparent angu lar diameter is 25", but. when farthest away ( i.e. in conjunction) its diameter is not more than 4". The axis of rotation is inclined 24u 50' to the plane of the orbit and therefore the planet presents phenomena of seasons similar to the earth's. The diurnal rotation period of Mars is known very accurately from observations of surface markings to be 24 hours 37 minutes 22.67 seconds. The planet shines with a red light and is a brilliant object in the heavens at midnight when near opposition. Mars has two satellites, discovered by Hall in 1877. They are very small. and visible with powerful telescopes only. The inner satellite.I'hohos, revolves around the planet in 7 hours 39 minutes, which is less than one: third of the Martian day. Consequently, Phobos will rise in the west and set in the east, its real motion more than counterbalancing the apparent diurnal motion of Mars on its axis. The outer satellite is called Deimos.
Beginning with the telescopic researches by Sir William Herschel, Mars has possessed special interest owing to the indication of the existence upon its surface of physical conditions not unlike those of the earth. The Martian seasons have already been mentioned. The 'canal system' of Mars, suggested by Sehiaparelli in 1S77. has given rise to a careful study of the planet, ren dered possible by the construction of our great modern telescopes. Many things seem to indi cate that Mars is enveloped in an atmosphere with physical properties similar to those of the earth's atmosphere. According to observations by Lowell, at Flagstaff, Ariz., carried on for six months, this atmosphere would appear to be of remarkable clearness. Two white patches, in the neighborhood of the poles, are very con spicuous and so brilliant that they. in the proper light of the sun, have been seen sparkling like stars. They are generally explained as acemnu lations of now and ice, and this view is sup ported by the fact that they change with the Martian seasons. i.e. increase in size during win ter, decrease as spring approaches, and almost disappear during the summer.
A mixture of orange patches and gray-green markings are seen extending over more than half the surface of the planet in a central zone, al most parallel to the equator. The orange patches are assumed to he land. This assumption is based upon the similar appearance that the great deserts of the earth would present under the same etaiditions. Also permanent markings on these patches have been observed. The gray green markings were at first explained to be seas and Sir Huggins discovered water in the atmosphere of Alars, but the recent observations of Douglass in Arizona (1891) and Barnard at the Lick Observatory (1896) seem to disprove the aqueous character of the 'seas.' In 1894 Lowell and Pickering discovered, a month after the Martian vernal equinox, a dark belt con nected with the south polar cap, which was ex plained loy them as a gathering of water resulting from the melting of the cap by the summer beat. A similar appearance has been observed around the north polar cap.
Of all the markings that have been observed on the surface of Alara, the 'canals' have created the most interest. Since their first observation at the very favorable opposition of the planet in 1877, they have been studied carefully at later favorable oppositions. They have been described by observers as faint lines. becoming finer and straighter at closer observation, following the course of great circles, and distributed like a network over the surface of the planet. Several appear to pass through the same point, at which round spots. called 'lakes.' are seen. Various theories have been advanced for the explanation of this 'canal system.' As the name indicates, they were first taken to be waterways, and the ehange in their appearance was explained as due to the Martian seasons. Piekering considered them to lie tracts of land rather than waterways. Lowell advanced the view that these 'canals' and 'lakes' constituted a system of irrigation, carried .out by the inhabitants of Alan: for the purpose of leading the water obtained from the melting snow of the polar regions over the entire surface of the These views are. however, to be taken with extreme caution. since the appearance of the canal system may be nothing but an optical illusion. See PLANurs: Sot An SYSTEM.