Page:The Music of the Spheres.djvu/276

 nent markings on its surface. The first thing one notices through a telescope is the ruddy color of its surface and the dark belt across the equatorial regions. The ruddy color is presumed to be the characteristic color of its soil, five-eighths of which is in a desert condition; there are also regions of other colors which are subject to change, and a white cap marking either pole.

The two white caps about the poles increase greatly during severe months of winter and vanish to small spots during the warmth of the Martian summer. These are the reservoirs of moisture for the planet. A series of photographs illustrating the phenomenon of the increase and decrease of these caps is very interesting, for at the height of the Martian winter, for instance, the north polar cap extends to the temperate zone while during the summer it dwindles until it is but a tiny patch a few hundred miles across. As the polar caps melt, they are bordered by a blue belt and this blue belt is only visible as the brilliant caps disappear. Judging from the same phenomena which are manifest on our earth, these polar caps were supposed to be snow. Through the aid of the spectroscope, they are now known to be snow.

The ruddy areas on Mars are interpreted as desert regions—great unfertile tracts of land but little affected by changes in climatic conditions, while the large irregular dark or blue-green regions are regarded as marshes or areas covered with vegetation, since they invariably grow darker during the Martian summer and reveal themselves in massed colors changing from the initial blue-green to ocher and finally to chocolate-brown. These changes follow the melting of the polar caps and each hemisphere undergoes the change in turn. Mars, however, is best known and famous for the theory of its so-called "canals."

The "canals" were first observed by Schiaparelli, the distinguished Italian observer, in 1877. Schiaparelli thought that the dark irregular areas were oceans and that they were connected