The Author. Perfectly correct. Thus, our solar world is not unique, it is only one member of the family of stellar worlds, which resemble our world in the disposition and the motions of the stars within them. The universe is composed of the agglomeration of them all. You know all this, but there is one fact which, as it is the result of recent discoveries, you may not be aware of; it is, the great variety of disposition or of physical aspect presented by certain stars, in which a kind of overturn of that which constitutes nature on our globe has taken place. While they remain similar to our world in the order of their movements, certain stars differ widely in the forces which govern nature in them.
Theophilus. Pray explain your meaning.
The Author. While our solar system is governed by a single central star, there are stellar systems which are governed by two, three, and even four suns. It is evident that worlds which have two or three centres of light and heat must present physical and mechanical peculiarities of which we have no idea. There are also other differences proper to many of the stellar worlds. The light of our sun and of the greater number of the stars is constant: it never undergoes either augmentation or diminution. But this is not the case with many of those distant suns which we call stars. We see their light alternately fade and revive; sometimes they shine brightly, then become almost imperceptible, and anon brilliant again. Some of them become altogether extinct. The decrease in lustre of several stars has been noted by different astronomers.[23]
Stars which have been observed in other times no longer exist.[24] Others have suddenly appeared, shone with excessive lustre, and at the end of some years have been seen no more.
These successive augmentations and diminutions of luminous brilliance are not uncommon in the stars with which we are acquainted. According to M. Flammarion,[25] star ο of the Whale varies very much in luminous intensity and the constellation itself frequently disappears. Star χ of the Swan passes from the fifth to the tenth size under our eyes, the thirtieth star of the Hydra, which is of the fourth size, almost always disappears at intervals of 500 days. These variations must, as M. Flammarion observes, produce strange results. To-day, the radiant star is shedding floods of light and fire upon the planets which it governs, and the soul of that planet is warmed by its burning rays. A few months later, without the least cloud in the sky, the shining of the sun becomes fainter, and then, by degrees, the obscurity increases, until at length the planet is plunged into thick darkness. When the diminution of the light of the sun is periodical, this universal night lasts for a fixed time, at the end of which the light returns, if not, the darkness is dispersed after varying periods. The light grows, little by little, until at length the radiant star reappears in all its primitive brightness. The fine days, the glorious light returns, until the moment when the same fading recommences and the darkness sets in once more.
Can we picture to ourselves the strange alterations which nature undergoes in regions which are subjected to torrid heat and glacial cold by turns? I am convinced that the glacial period which geologists have defined in the history of our globe, during which an extraordinary and sudden lowering of the temperature caused the death of multitudes of living beings, and covered Europe with glaciers from the mountains—was caused by a momentary weakening of the intensity of the sun's light. When it resumed its ordinary brightness, the sun dispersed the ice which had covered the earth with a death mantle.[26]
I have said that there are double stars, that is to say, worlds illuminated by two suns, and sometimes even by three or four. It is a strange fact that in almost every instance one of these suns is white, like ours, but the second is coloured, blue, red, or green. In the constellation Perseus for example, a double star can be distinctly seen by the aid of a good telescope. The star η is in fact accompanied by a second, which makes part of the same solar system. Now, this second star is blue. In the constellation Ophiochus there is a similar system of double stars, one of which is red and the other blue. The same peculiarity exists in the constellation of the Dragon. In a double star of the constellation of the Bull, there is a red sun, and a blue sun. There are double solar systems red and blue; such are the constellations Hercules and Cassiopœia. Other double solar systems are yellow and green, and sometimes yellow and blue. In all the worlds which are illuminated by these coloured suns, the effect of light must be very strange. No painter could represent them, and indeed we, who know only the white light of our own sun, cannot form any idea of them.
Theophilus. These features of the stellar worlds are very interesting, and I am glad to learn them. But are we not straying from our subject?
The Author. No. After having made you understand that the solar system which we inhabit is only a member of an immense family of other solar worlds, only a small fraction of the universe, I wished to show you by the diversity of those worlds, the facility with which nature varies the forces and the physical conditions proper to the stellar worlds, and consequently the living and inanimate types which make a portion of these different stellar worlds. Now that you understand the prodigious diversity of the solar worlds which compose the universe, I will go on to our principal object. I have not lost sight of my intention of proving to you that the universe has no limits, that in its extent it is really the Infinite. I am now approaching this great question. By the consideration of the stars, I am going to bring out into relief the immeasurable vastness of the universe. Let me speak, first, of the appalling distances which separate the stars from the earth, and the figures will show you that on that side we fall into the Infinite, and then I will speak of the numbers of the stars which people space; and on this side also the abyss of the Infinite will yawn before us. First, as to the distances which separate the stars from the earth, from whence we may logically infer the distances which separate these stars from one another. The distance between the earth and the sun is 38,000,000 leagues, and this shall be our unit, our standard of measurement, by which to estimate the distance of the stars.
I do not know, my dear Theophilus, whether you have formed an exact idea of this extent of 38,000,000 leagues, which lie between us and the sun. In general, we can only conceive prodigious distances such as astronomy deals with, by representing them by the interval of time which certain movable bodies known to us would consume in traversing them. Let us then have recourse to comparisons of this kind. A cannon-ball weighing 12 kilogrammes, exploded by 6 kilogrammes of powder, proceeding at a uniform rate of 500 metres a second, would take 10 years to travel from the earth to the sun.