When, on a fine starry night, we examine this world through the telescope, when we see the polar snows which melt in the spring, the finely marked continents, the mediterraneans with long gulfs, the eloquent and varied geographical configuration, one cannot help asking whether the Sun which illuminates that world as it does ours shines on nothing living, whether those rains fertilise anything, whether that atmosphere is breathed by any living being, and whether that world of Mars which rolls swiftly through space resembles a railway train travelling empty without either goods or passengers. The idea that the Earth where we are could swing round the Sun as it does without being inhabited by any creature whatever appears so absurd as to be hardly worth thinking about. By what permanent miracle of sterilisation would the forces of nature which act there as they do here have remained eternally inactive and barren? * * * * * It is therefore conceivable that one might apply to Mars the plan originally proposed for the Moon. The distance of that planet is such that although it is much larger than the Moon in volume, it appears 63 times smaller when it is nearest to us. Yet one may understand that a telescope which magnifies 63 times enlarges Mars to the size of the Moon as seen with the naked eye, and that a magnification of 630 gives it a diameter ten times larger than that of our satellite. Yet if ever the attempt is made to put any sort of project of communication between us and Mars into practice, the signals would have to be carried out on a much vaster scale. It would not be triangles, squares, circles, of several miles which would have to be constructed, but figures of 70 miles or more, always supposing (1) that Mars is inhabited, (2) that these inhabitants occupy themselves with astronomy, (3) that they have optical instruments analogous to ours, and (4) that they carefully observe our planet, which to them is a brilliant star of the first magnitude, the morning and evening star, and in fact the brightest heavenly body. Is this fourfold hypothesis acceptable! If that question were put to the vote of the citizens of the Earth, without asking the opinion of the Central African savages or the South Sea Islanders, but only the numerical majority of the European population, one may safely wager that they would not even understand the question, for the majority of mankind does not know that the Earth is a planet and that the other planets are Earths.