# Popular Science Monthly/Volume 50/April 1897/Life on the Planets

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* LIFE ON THE PLANETS.
By M. J. JANSSEN.
(HAVING shown how all astronomical discovery, concluding with spectrum analysis, points to a similarity of constitution in the earth and the heavenly bodies, M. Janssen continues:)
All this whole forms a single family, the members of which have a common genesis and have been formed with the destiny of becoming worlds like ours. Their movements around the central star which enchains them by its powerful attraction are subject to the same laws, and that star, by virtue of its high temperature and the immense reserves of force it contains, sheds upon them ​those influences and radiations which go to place upon their surface the generative elements of life. Yet while these stars present so strict analogies in formation and nature, they do not by any means indicate the same degree of advancement in what may be called geological or rather planetary evolution, or that which tends to the appearance and development of life on their surface. Here the conditions of mass, of distance from the sun, and doubtless other circumstances still unknown, come in to order the epoch and the extent of these developments; but we can affirm, without going beyond the inductions permitted by the condition of science, that if life has not yet been established directly on the surface of any of the planets, we have very strong reasons for assuming its existence on some of them. We may regard this conclusion as gained from the long labors of antiquity and modern discoveries.
We say that, while the problem has not been directly resolved by the eyes, it has been worked out by an aggregate of facts, analogies, and rigorous deductions that leave no room for doubt. This is the mature and perfect fruit of science. It is the view of intelligence, as certain an authority and of even a higher and nobler order than the senses. I say further that what we know of the unity of the chemical composition of the matter of the sun, the stars, and the nebulæ permits us to make new inductions respecting the part performed by the bodies which are on the earth the most important factors of the phenomena of life. It is thus infinitely probable that hydrogen, oxygen, nitrogen, carbon, and especially water, which on the earth are the indispensable constituents of vegetable and animal life, fill a like office not only in the planets of our system, but throughout the universe.
Water in particular, by virtue of its chemical functions and the properties with which it is endowed in the solid, liquid, and gaseous states—properties which are so admirably fit for the accomplishment of physiological processes—is a unique substance, and the search through the whole series of chemical compounds for any body that can take its place has been in vain. The discovery of the spectrum of the vapor of water permits us to deduce and assert its presence in the atmospheres of the planets and in those of a whole class of stars as well. Drawing from these results the fact of the presence of hydrogen, one of the generative gases of water, in nearly all the stars, we are justified in supposing an extreme diffusion of that important element from the point of view of the unity of the phenomena which control the production and maintenance of life.
Thus, the more science advances, the more is that great law confirmed and established of unity in the material elements, in ​the compounds formed of those elements, and in the constitution of the stars and the parts they perform in the grand whole.
Are we authorized now to assume from this a unity of forms that life may put on not only in the sister planets to ours, but also in the other systems of worlds scattered through the skies? May we especially push our inductions still further and higher, conclude from such material unity upon a mental and moral unity, and say that, as there is only one physics and one chemistry in the universe, there are also only one logic, one geometry, and one moral, and that the beautiful, the good, and the true are identical and of the universal order everywhere?
Science, embracing in its results only immediate and demonstrated facts, does not warrant us in going so far as this, but with the truths it unfolds to us seems to invite us toward it.
There were brilliant minds in antiquity, which upon bases otherwise restricted conceived and proclaimed verities concerning the world and the universe which the most modern science has only been able to confirm.
Let us, then, respect these cheerful speculations. If they are still only of things preconceived, who can affirm that science will not make them real to us to-morrow? By establishing the laws and harmonies of the material world, astronomy prepares us for the conquest of truths of a still higher order.
We can say then plainly that the subjection of natural forces and the reign of man over Nature are only the first fruits of science. It prepares other fruits for its votary of a higher and more precious order. By the beauty of the studies to which it invites him, by the grandeur of the horizons which it opens out to him, and the sublimity of the spectacle it gives him of the laws and harmonies of the universe, it promises to win him away from his present preoccupations, which are perhaps too exclusively positive, and will restore to him under a new form and in an incomparable grandeur that taste for elevated poetry, that enthusiasm for the beautiful, and that reverence for the ideal which are among the most imperious needs of the human soul and which it never abandons without peril.—Translated for the Popular Science Monthly from the Revue Scientifique.