On the other hand, the analysis of the movements of several stars, such as Sirius, Procyon, Altair, and many others, proves that these far-distant suns have companion planets as yet unrevealed by the telescope, and which possibly may never be discovered because they are dark and lost in the radiation of the star. The companion discovered in the neighbourhood of Sirius is not the only celestial body of that system. Scheiner speaks of about 10 million stars as constituting the sidereal universe. But the photographic chart of the heavens which comprises stars down to the thirteenth magnitude is already expected to contain 30 millions. If we go down to the lowest magnitudes we reach the figure of 100 millions. It is therefore not an army of 100,000 worlds which appears before us, but rather of several millions.

Now, this is a point of the greatest importance for the exact appreciation of the problem.

The terrestrial organisms from the lowest up to man are the result of forces in action on the surface of our planet. The first organisms seem to have been produced by combinations of carbon with hydrogen and oxygen, and their life consisted, so to speak, only in a few rudimentary sensibilities. Sponges, corals, polypi, medusæ, give us an idea of these primitive beings. They were formed in the warm waters of the primary ages. While there were yet no continents nor islands emerging from the universal ocean, there were no air-breathing organisms. The first aquatic beings were succeeded by amphibia and reptiles. Afterwards came the mammalia and the birds. The constitution of beings stands in close relation with the substances of which they are composed, the medium in which they live, the temperature, the light, the density, gravitation, length of day and night, seasons, etc.—in a word, all the cosmographic elements of the planet.

If, for example, we compare two such worlds as the Earth and Neptune, which differ very much as regards distance from the Sun, we cannot imagine for a single instant that the organic forms should have had the same development. The average temperature must be much lower on Neptune than on the Earth, and so must the intensity of light. The years and the seasons are 165 times longer than with us; the density of materials is three times less, and gravitation, on the other hand, is a little stronger. Under conditions so different from ours, the activities of Nature can only have been shown in other forms. The elements also are not found present in the same proportions, and spectrum analysis has even shown us that substances which prevail in the atmospheres of Jupiter, Saturn, and Uranus, as well as Neptune, are different from those which constitute our organisms. Lungs functioning in another atmosphere would have to be different from ours. The same applies to the stomach and the digestive organs. Chemical constitution is not even the same. Instead of carbon as a fundamental element associated with hydrogen, oxygen, and nitrogen, we can imagine with Scheiner silicon and other bodies. We must conclude that the organs and the senses cannot be the same as they are here. The optic nerve, for instance, which has been formed and developed here from the rudimentary organ of the trilobite to the marvels of the human eye, must on Neptune be incomparably more sensitive than it is in our blinding sunlight and must perceive radiations which we do not perceive here. It may even be replaced by another organ. The bodily forms, animal and human, can resemble nothing on earth.

Certain savants object that, if the conditions are too different from terrestrial conditions, life cannot exist at all. But we have no right to limit the powers of Nature by the narrowness of our sphere of observation, or to pretend that our planet and our human race are the model for all planets. That is an hypothesis as infantile as it is ridiculous.

Others go still farther, and imagine that life only appears on Earth, and that we have no sufficient reason to suppose that on other globes it has been the result of inorganic evolution. This, as we have often repeated, would be a strange interpretation of the language of Nature, considering that our small planet is too small a cup to contain the whole of life, that that life abounds everywhere, fills the waters, swarms in the air, covers the entire surface of the globe, and that the fertility of Nature is such that she multiplies parasitic life at the expense of life itself, rather than get tired of producing. And the spectacle is the same for all the immense duration of the geological eras. Quite lately, noticing a heap of fossils of the secondary era by the roadside in the country, I took a stone to put it into a collection, for it was entirely made up of shells petrified and cemented in a block. In taking it up I exposed a swarming mass of living beings, small snails, wood-lice, beetles; and I caught two lizards; while butterflies laid their eggs in the plants around. Life of former days, life of to-day, life everywhere. Life always!

Certain minds are capable of supposing that for the whole duration of its existence, for millions of years, a world could come to nothing but the state of dead and barren rock and that the life which swarms on the surface of our planet is only a freak due to the fortuitous combination of elements of fruitfulness, a parasitism of more or less large fleas which might never have been produced at all. But that is a hypothesis contrary to the observation of Nature, and difficult to maintain seriously except as a pure play of the imagination, which does not satisfy the most elementary logic. And though our logic may not be that of Nature, yet we must not stray too far away from it if we want to reason.

But as we have already repeated so often in this book, and what we must thoroughly absorb, is the importance of time as well as of space. Just as our world is nothing but a small island, a point in the universe, so also our era is nothing but a moment in eternity. The present moment has no more importance than the moments which have preceded or those which are to come. There is no reason to believe that such and such other worlds are inhabited at present simply because we live at present and can observe them. One world has been inhabited in the past, another will be inhabited in the future. Let us not be personal, like infants or the aged, who see only their own room. Let us know how to live in the infinite and in the eternal.

INDEX