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Page:Popular Science Monthly Volume 24.djvu/263

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SURFACE CHARACTERS OF THE PLANET MARS.

the meridians of 40° and 120°. It extended only over the yellow-portions, which are supposed to be continents, and often covered the canals, but completely avoided the darker portions, which represent the oceans and larger lakes. It was not a contiguous covering, but consisting of white or whitish spots, which were irregularly distributed.

The atmosphere of Mars appears to have been more transparent than during 1877. Not only the luminous and the opaque zone of the rim were smaller, but in some parts of the planet the contrast between the light and shade was more distinctly visible with an inclined illumination, and so it was possible to more readily distinguish objects at the edge of the planet than at the center.

During November the north pole advanced some 7° to 8° within the circle of the visible hemisphere; but the hope of being enabled to examine the surface in the vicinity of this pole was unrealized on account of the unfavorable weather. For this reason the limit of the chart of 1881-'82 does exceed 60° north latitude, and, hence, does not extend much beyond the portions explored in 1879; but the parts lying between 30° and 60° northern latitude could be more closely examined. On this occasion also the lower end of the chart is limited by a series of dark stripes which appear to be connected with the northern ocean. The peculiar character of the surface of Mars can not, however, be well explained until after the next opposition. It was impossible to explore the southern ocean with exactness beyond 50° south, although all of the islands which had previously been recognized were observed as white spots similar to the polar snow. All of the smaller seas which branch off from the equator were very distinct in their configuration. The continents and the interior lakes between the bright equatorial zone and the south ocean could be drawn with the greatest accuracy. A few changes in the appearance of particular portions as compared with their shape in 1879 were noticed, and as hundreds of thousands of square kilometres of surface, which were formerly light, had in the mean while become dark, so on the other hand many of the sections which previously were dark now became luminous. These changes prove that the darkening principle which produces them is due to something which is movable and extends over the surface of the planet (for instance, water or some other liquid), or perhaps something capable of being transmitted from place to place (such as vegetation).

Not one of the old dark lines which have been called "canals" was missing, and causes which in all probability were due to the sun produced numerous phenomena, which in former oppositions were only suspected. That brilliant, light-red color mixed with white, which in 1877 occupied the whole of the equatorial zone and a large part of it in 1879, was found in 1882 to be entirely absent. Undefined shadows began to form in this luminous veil surrounded by stains of