changes have been recorded by the photographic plates. The great difference between Mars and the Moon depends upon the existence of a real atmosphere on the former. The oxygen will probably vanish from Mars also, being used up in the course of disintegration. But nitrogen, argon, and the other permanent gases will always remain, as will the water vapour from the bodies of water ever present, particularly around the south pole. It is true that this water vapour also will diminish with sinking temperature and when the latter finally has reached the freezing point of the salt solutions on Mars, the canals and the lakes will cease to thaw out or liquify under the vapour distilled over from the warm to the cold pole. But sand storms and thin mist formations will always appear and cause colour changes on the desolate planet. If we wish to picture to us the future fate of our Earth when it gradually enters the reign of darkness and cold in consequence of the enfeebling of the Sun, we must seek our illustration on Mars and not on the Moon. Slowly are the oceans going to freeze, finally down to their bottom, the abundance of the rainfalls will diminish, only light snow will now and then bring change to a surface evermore transformed into a sand desert as far as the continents reach. Rents in the rocky substrata of the latter will appear as dark lines, caused by the gases rising from the interior. When the temperature at the equator has fallen below the freezing point, the polar regions will remain the only parts where a light covering of frost will melt in the height of the summer season and where the last feeble organisms will eke out their hard existence, resorting to a prolonged winter’s sleep of their seeds and spores. Finally, the last remnant of life will also disappear and sandstorms alone, save for the gasps of gas emanation from fissures in the rocky ground, will bring relief to the monotonous desolation. Falling meteoric dust, which now exists in original state only on the bottom of the oceans, will gradually cover the entire surface of the Earth with a mantle coloured brick-red through the influence of atmospheric oxygen. When the oxygen itself is used up, the meteoric dust will retain its original greyish-green hue and lend it to the funeral pall of the Earth.