Many points of light which were undoubtedly stars, and merely stars, were shown on this picture taken by the German astronomer at Urania. Among these points of light was, however, one object which, though in appearance hardly distinguishable from a faint star, was in truth a body of a very different character. No telescope, however powerful, would show by mere inspection any appreciable difference between the dot of light indicating a star and the dot of light indicating the asteroid Eros. The fundamental difference between the star and Eros was, however, revealed by the long exposure. The stars in such a picture are, of course, at rest. They have occupied for years and for centuries the places where we now find them. If they are moving at all, their movements are so slow that they need not now be considered. But this starlike point, or, as we may at once call it, this asteroid, Eros, is moving. Not that its movements seem very rapid from the distance at which alone we are compelled to view it. No casual glance would indicate that Eros was flying along. The ordinary observer would see no change in its place in a second—no change in its place even in a minute. But when the exposure has lasted for an hour this asteroid, in the course of the hour, has moved quite appreciably. Hence arose a great difference between the representation which the photograph has given of the stars, properly so called, and of the asteroid. Each star is depicted as a sharp, well-defined point. This little body which is not a star, this unsteady sitter in the picture, could not be so represented; it merely appeared as a streak. The completed photograph accordingly shows a large number of well-marked dots for the stars, and among them one faint line for the asteroid.
Such a feature on a picture, though very unusual, does sometimes present itself. To detect such a streak on a photograph of the stars is a moment of transcendent joy to the astronomer. It is often for him the exciting occasion on which a discovery is made. This little moving point is in actual fact as different from a star as a pebble is different from a brilliant electric light. The resemblance of the asteroid to a star is merely casual; the resemblance would wholly disappear if we were able to make a closer inspection. The star is a brilliant blazing orb like a sun, but so far away that its luster is diminished to that of a point; the planet is comparatively near us; it is a dark body like our earth, and is like our earth also in this further respect that all the light it enjoys has been derived from the sun.
Though there is this immense difference between a star and a planet, yet the observer must not expect to notice any such difference by merely taking a peep through the telescope. It was only the long exposure in the photograph that revealed the little body.
Such is the manner in which an asteroid is generally discovered in these latter days. A discovery like this comes as the well-earned reward of the skill and patience of the astronomical photographer. There are, indeed, a large number of known asteroids; our catalogues contained four hundred and thirty-two of them up to the time when Witt exposed his now famous plate. Had the asteroid Witt then found been merely as other asteroids, it would never have received the prominent position that has now to be assigned to it in any account of the astronomy of the century. That object found by Witt on this night which is to be henceforth memorable in astronomy is of a wholly exceptional kind. Had Eros been merely an ordinary asteroid, Witt might no doubt have received the credit to which his labors and success would have entitled him. Another asteroid would have been added to the long list of such objects already known, but the newspapers would never have troubled their readers about the matter, and the only persons who would have been affected would have been the astronomers, and perhaps even among them no particular sympathy would have been felt in certain quarters. Those particular astronomers to whom has been intrusted the special work of looking after the asteroids and of calculating the tables of their movements might even have received with no very great enthusiasm the announcement of this further addition to the burden on their heavily laden shoulders.
I have said that Eros is quite a small globe; it may be well for us fully to realize how small that asteroid actually is. If the moon were to be crushed into two million equal fragments, each of those parts would be as big as Eros. If the whole of Eros were to be covered with houses, the city thus formed would not be so large as greater London. So far as mere size is concerned, Eros is quite unimportant. We can further illustrate this if we compare Eros with some of the other planets. The well-known evening star, Venus, the goddess of love, is a hundred million times as big as that tiny orb we now call Eros, the god of love. After all this it may seem strange to have to maintain what is, however, undoubtedly the fact, that the discovery of Eros is one of the most remarkable discoveries of this century.
Until Eros was discovered, our nearest neighbors among the planets were considered to be Venus on one side and Mars on the other. The other great planets are much more distant, while, of course, the stars properly so called are millions of times as far.
Great, then, was the astonishment of the astronomers when, by the discovery of Eros, Mars and Venus were suddenly dethroned from their position of being the earth’s nearest neighbors among the planetary host. This little Eros will, under favorable circumstances, approach the earth to within about one third the distance of Mars when nearest, or about one half the distance of Venus when nearest. We thus concentrate on Eros all the interest which arises from the fact that, the moon of course excepted, Eros is the nearest globe to the earth in the wide expanse of heaven. To the astronomer this statement is of the utmost significance; when Eros comes so close it will be possible to determine its distance with a precision hitherto unattainable in such measurements. Once the distance of Eros is known, the distance of the sun and of all the other planets can be determined. The importance of the new discovery arises, then, from the fact that by the help of Eros all our measurements in the celestial spaces will gain that for which every astronomer strives—namely, increased accuracy.
Seeing that the existence of intelligence is a characteristic feature of this earth, we feel naturally very much interested in the question as to whether there can be intelligent beings dwelling on other worlds around us. It is only regrettable that our means of solving this problem are so inadequate. Indeed, until quite lately it would have been almost futile to discuss this question at all. All that could then have been said on the subject amounted to little more than the statement that it would be intolerable presumption for man to suppose that he alone, of all beings in the universe, was endowed with intelligence, and that his insignificant little earth, alone amid the myriad globes of space, enjoyed the distinction of being the abode of life. Recent discovery has, however, given a new aspect to this question. At the end of this century certain observations have been made disclosing features in the neighboring planet, Mars, which have riveted the attention of the world. On this question, above most others, extreme caution is necessary. It is especially the duty of the man of science to weigh carefully the evidence offered to him on a subject so important. He will test that evidence by every means in his power, and if he finds the evidence establishes certain conclusions, then he is bound to accept such conclusions irrespective of all other circumstances.
Mr. Percival Lowell has an observatory in an eminently favorable position at Flagstaff, in Arizona. He has a superb telescope, and enjoys a perfect climate for astronomical work. Aided by skillful assistants, he has observed Mars under the most favorable circumstances with great care for some years. I must be permitted to say that, having carefully studied what Mr. Lowell has set forth, and having tested his facts and figures in every way in my power, most astronomers have come to the conclusion that, however astonishing his observations may seem to be, we can not refuse to accept them.
No one has ever seen inhabitants on Mars, but Mr. Percival Lowell and one or two other equally favored observers have seen features on that planet which, so far as our experience goes, can be explained in no other way than by supposing that they were made by an intelligent designer for an intelligent purpose. Mr. Lowell has discovered that there are certain operations in progress on the surface of Mars which, if we met with on this earth, we should certainly conclude, without the slightest hesitation, were the result of operations conducted under what we consider rational guidance.