This remarkable development of public curiosity is easily explained by the marvellous achievements of contemporary astronomy and the admirable precision of certain results obtained. Unless one has a stone instead of a heart and a lump of fat in the place of a brain, it is difficult not to feel some emotion over the achievements of science. If we declare, for instance, that we know the general geography of Mars better than we do that of our own planet, the listener or reader is at first inclined to be somewhat sceptical. But if we show him, either in a telescope or in a diagram, the snows of the north or south poles of Mars, he will admit that nobody has as yet had a complete view of these regions on the Earth, in spite of the discoveries of polar explorers, and he will be convinced that we do know those Martian regions better than our own poles. That is already a fact of some interest; but we can go farther than that. It is not only the pole, but the whole surrounding country that is better known on Mars than on the Earth, not only from the geographical, but also from the meteorological point of view. Thus, for instance, we can almost constantly measure the extent of the polar snows, and we find that it varies with the seasons. We see with our own eyes the melting of these snows taking place very rapidly under the light and heat of the Sun, night after night, so to speak, during a summer which is twice as long as ours. The snows disappear almost entirely, and only a little ice remains on a region which we know, and which represents the pole of extreme cold, situated 212 miles from the geographical pole. In spite of the perseverance and heroism of arctic explorers, none of these climatological facts have been witnessed on Earth. It is possible that the Martians are ignorant of their own phenomena if they have been unable to reach their poles. Still, since their poles are free at the end of the summer, they are much better able than we to explore their polar regions. We may say that in general the meteorology and climatology of Mars are better known than those of the Earth. At the time when you read these lines you do not know, and nobody can tell you, what sort of weather you will have to-morrow. But we do know almost certainly what the weather will be to-morrow, next week, next month, on such and such a region on Mars: if we do not wait till the winter comes, we know that it will be fine. Hardly do we see a cloud between the vernal equinox and the autumnal equinox, neither in the equatorial nor the temperate regions, and hardly even in the circumpolar regions. If we are unable to make a drawing of the telescopic image of the planet, the difficulty hardly ever arises from the Martian atmosphere, but from our own, which is so often overcast or turbid. All the geographical configurations, seas, rivers, plains, covered with vegetation according to the moisture available, water-courses varying with the seasons, canals and oases, are mapped