prevail as they do here; and the intensity of the seasons is absolutely the same as with us, the inclination of the axis being the same as ours.
If it were ever attempted to put into practice any project for the communication between this world and ours, the signals would have to be established on a very vast scale. It would not be a question of triangles, squares, and circles of some kilometres in size, but of figures more than a hundred kilometres large. Moreover, it would always be on the hypotheses that, there are inhabitants of Mars, that these inhabitants understand astronomy, that they have optical instruments analogous to ours, and that they observe our planet with interest. This planet must be to them a star of first magnitude, the evening and morning star, the brightest star of their heavens.
When on a beautiful starry night we examine Mars under a telescope, when we see the polar snows, which melt at spring-time, those finely defined continents, those long gulfed Mediterraneans, this eloquent and varied geographical configuration, one cannot but ask oneself if the sun which illumines a world so like our own does not likewise shed light on living beings, if the rains do not fertilize crops, if this atmosphere be not inhaled by beings, or if this sphere of Mars, which turns with rapidity in space, be like an empty train on a railway—containing neither passengers nor goods.
The idea of the planets with which we circulate, as Mars does, round the sun not being inhabited by any creatures whatever is too inconsistent to be conceivable. By what permanent miracle of sterilization can the forces of nature which act there as here remain eternally inactive and barren?
We have so far only spoken of life and animated matter; what is, then, this life? and what is this animated matter?
We can as little apprehend the essence of life and animated matter as that of gravity, which is infinitely more simple in its manifestations than what we call the vital force. We only know in our world that the vital force is united to an especial form of matter—organized matter—and that when this disappears it ceases to be vital force, and transforms itself (as force can never be destroyed) into other forms of energy. For these facts it matters little whether we admit the vital force as a special force or consider it as a particular aspect of a known force like electricity. From this intimate association of the vital force with organized matter it seems that the vital manifestations (repairing tissue, growth, reproduction, etc.) can only take place under conditions in which the organized matter can exist; in all other cases the manifestations of life cease and death ensues, or the vital force remains inactive until the exterior condition becomes favorable.
Our problem of the habitability of the stars is, then, limited to observing the celestial bodies upon which the conditions are such that organized matter can exist in a durable form.
In the planet Mars the density of a cubic metre of water, earth, or any matter is only the seventeenth of what it is here, and the weight is only 38-100ths. A kilogram transported to Mars would therefore only weigh 376 grams there, and a man or woman weighing 70 kilos would only weigh 26 there. The years, as I remarked, are nearly twice as long as upon our planet, and the climatological conditions seem much more favorable than they are here.
The conditions necessary to life are, we know, multiform, as the structure of the organic matter is so complicated.
The more simple the organism, the more simple are its conditions of existence, and generally the greater the power to resist unfavorable conditions.
The animals and plants which live in caves or in vast depths in the sea are deprived of light, but being accommodated to this privation, they do not suffer from it. Animals have need of oxygen in the air or in the water; plants, moreover, require a little carbonic acid for the constitution of their tissues. There are even some animalculæ to which oxygen is a poison. Generally a temperature above 50° Cent. (122° Fahr.) cannot be borne. This means that at this temperature albumen, one of the most important of the substances in the animal organism, coagulates.
Some inferior beings can bear the highest temperatures, and even endure for some time a temperature of 100°
