Mars has, it seems, an atmosphere, even as earth has. Of all the planets Mars, is the only one whose actual surface is discernible in the telescope. Mercury and Venus are so hidden by dense envelopes of clouds that the real planets within are only now and then to be dimly caught sight of. Jupiter and Saturn are so completely enwrapped in mighty masses of vapor, that we can not even be certain whether there are any solid bodies at all inside. But Mars can be studied. Here and there, it is true, clouds sweep over the landscape, hiding from view for a little while one continent or another, one sea or another, growing, changing, melting away, as do the clouds of earth. Still, though these clouds come and go, there are other markings on the surface of Mars which do not change. Or, rather, they only change so much as the continents and oceans of earth would seem to vary, if watched from another planet, as the daily movement of earth carried them from west to east, or as they might be hidden for a while by cloud-layers coming between. It has been curiously noted that these clouds over Mars form often in the morning and evening, and are afterwards dispersed by the heat of midday. Also there seems every reason to believe that rainfalls take place in Mars as upon earth. The red color of Mars is well known. This does not vanish in the telescope, but it is found that parts only have the red or orange hue, while other parts are dark and greenish. These are the markings which remain always the same, and they have been so closely examined that more is known about the geography of Mars than of any other world outside our own. Mars, at his nearest point, does not draw closer to us than forty millions of miles. At such a distance one must not speak too confidently. There are, however, many reasons for believing that the red portions are continents and that the green portions are oceans. The spectroscope has lately shown us that water does really exist in the atmosphere of Mars--unlike the dreary, waterless moon. So we no longer doubt that the cloudlike appearances are clouds, and that rain sometimes falls on Mars. If there is rain, and if there are clouds and vapor, there are probably oceans also.