The inclination of his axis to the plane of the orbit is such that his seasons would be very similar to ours. It is difficult to reconcile the idea of an extensive vegetation with his peculiar red colour; it is just possible, however, that some of the green patches, generally supposed to be seas, may in reality be large forests. The most valid objection to the habitability of Mars lies in the fact of the extremely low atmospheric pressure, which, as we have seen, would probably average about five inches of mercury. The lowest pressure that a man has ever lived in, even for a short time, is about seven inches, which was reached by Coxwell and Glaisher in their famous balloon ascent. The aëronauts, however, narrowly escaped perishing, not only on account of the low pressure, but also because of the extreme cold. It seems impossible that a man constituted exactly as we are could live for any length of time breathing air only one-sixth of the density of ours. But it is rather going out of our way to assume that the Martialites would be exactly the same as we are in every way; the chances are a million to one against it; and on the other hand, a very slight modification of the lung arrangement would suffice to make life perfectly possible under such conditions. The nights on Mars would be very dark, for he has no satellite like our moon. He has, it is true, two moons, but they are so small that their illuminating power is _nil_, being respectively only sixty and forty miles in diameter. The smallest of these presents the curious phenomenon that it revolves round Mars faster than the planet turns on his own axis, and therefore would appear to rise in the west and set in the east. Our earth, as seen from Mars, when at his nearest, would appear about the same size as Jupiter does to us; that is to say, would subtend an angle of about forty seconds. At his furthest distance, this would be reduced to fourteen. We thus see that there is ample reason for assuming that this, the most interesting of all the planets, is the abode of creatures not essentially different from ourselves. Being considerably older than we are, the Martialites are probably much further advanced in the arts and sciences; and perhaps there may be some truth in the story of the Italian astronomer who says he has lately detected lights on the planet moving about in such a way as seems to indicate a deliberate intention to open communication with the earth. What the language of the lights is, we have not been informed; let us hope it is something more practical than the proposal of the Russian savant to communicate with the moon by cutting a huge figure of the forty-seventh proposition of Euclid on the plains of Siberia, which, he said, any fool would understand. IN ALL SHADES. CHAPTER XXX.