Dreams of an astronomer

by Camille Flammarion

It is with these words that Kant in his Natural History of the Heavens terminates the last chapter, which treats of the habitability of the planets. They come from the soul of every thinking man who has preserved the spark of the ideal. The aspect of the starry sky awakens all those who are not among these vulgar spirits the same sensations which manifest themselves in various ways according to the education of him who experiences them and according to his momentary disposition. The astronomer also is delighted by this spectacle in spite of his regular observation of the sky. The astronomer sees farther and clearer into the celestial spaces than the ordinary man, his knowledge leads him by rapid deductions to vast considerations until he suddenly reaches a point where, for the time being at all events, an insuperable barrier presents itself to the human spirit, and where an imperious halt reminds him of the truth that all science is incomplete. The ordinary man looks upon the sky in quite a different way, and so does a woman. To both, the spectacle of the starry sky offers an enjoyment independent of all research and all preoccupation. A purely æsthetic pleasure.

Are these stars inhabited? Are they inhabited by thinking beings? Do love and hate reign there as they do here? Such are the questions which occur at once. Afterwards, in hours when the need for hope and consolation is felt, the desire arises to contemplate some day with our own eyes the splendours of those other worlds and to be able to soar up to them. The most brilliant stars are the special objects of such wishes, and if they could be fulfilled a population of loving souls would reside on these same stars: Sirius, Vega, Venus, and Jupiter.

The question of the population of the celestial bodies is as ancient as the discovery of the individual existence. It has always occupied thinking humanity, and many have sought to raise the veil which hides the answer. We, also, should like to take a step towards this solution, and it is with that object that we propose to quote here the actual facts bearing upon the conditions of habitability of the celestial bodies and to draw the most probable conclusions. We can combine the astronomical data with the most recent use of physics, and, thanks to the progress recorded by these two sciences in the last ten years, we may be able to draw some new conclusions.

(Here the author passes in review the older writers, Huygens, Kircher, and Fontenelle, which I have summarised in my two books called The Plurality of Inhabited Worlds and Imaginary Worlds. He arrives eventually at the nineteenth century and at Gruithuisen, whom my readers know less.)

HISTORICAL

Huygens, the most celebrated mathematician and physicist of his epoch (1629-95), takes it for granted that all the planets are inhabited (he does not speak of the Sun or stars), and that consequently all of them offer the conditions vital and essential to us, that is to say air and water. He easily refutes the objections based upon the distance of the planets from the Sun. He supposes that the water on the other planets will have quite other qualities than ours; on Mercury, for instance, it would only boil at a very high temperature, and on Saturn—at his time the outermost planet known—it would not freeze at the lowest temperature then conceivable. The mass of Jupiter compared with that of our own globe would suggest that its air must be very dense and that its inhabitants could swim in it; but the Jovians would easily accommodate themselves to this state of things. He supposed that the mind of the inhabitants of the other planets was about the same as ours and that their organism was analogous to our own; for what would be the object of the Sun illuminating those other planets if their inhabitants had no eyes? One might indeed think that different species of reasonable beings might exist, but not on the same planet, for they would be in mutual conflict, would struggle for supremacy, and do each other every kind of harm.

He gives a very naïve refutation of an opinion given before him that the height of the inhabitants would have to be inversely as the volume of the planet and consequently the men on Jupiter would not be bigger than the mice on the earth. This, he says, is not possible, because such small beings would not, as astronomers, be capable of using large telescopes.

An important question, according to Huygens, is whether the intelligence of the inhabitants has any relation to their distance from the Sun. He inclines to believe that the inhabitants of Mercury are much more intelligent than we on account of the greater force and vitality of their spirit due to the greater heat of the Sun, but this is not confirmed by what happens on our own globe. The same reason would lead one to believe that the inhabitants of Jupiter are much less intelligent than ourselves, although its four satellites would offer to the mind material for profitable astronomical studies.

What is also evident is the small value of a purely logical and philosophical reasoning based on insufficient premises. We see how a man of sense and judicious spirit can be led to absurd conclusions when he is burdened with preconceived ideas and incomplete knowledge. We shall have several more occasions to bring out this fact, and that is why we have avoided pretending to resolve the question we have put. The deductions which we formulate to-day may be reversed to-morrow by new discoveries furnished either by experience or by theory.

Apart from his decided opinion concerning the habitability of all the planets, Huygens draws his conclusions logically enough, inasmuch as he bases his affirmations on the knowledge of his time.