Let us turn lastly to the amazing comet of the year 1744. We find that though it had the longest period of any which has ever been assigned to a comet as the result of actual mathematical calculation, yet its range in space would scarcely suffice to change the position of the stars in such sort that the aspect of the familiar constellations would be materially altered. Euler, the eminent mathematician, calculated for this comet a period of 122,683 years, which would correspond, I find, to a distance of recession equal to 2,469 times the distance of the earth from the sun, or about eighty times the distance of Neptune. Yet this is but little more than twelve times the greatest distance of the comet of 1811. Probably the actual range of such an orbit from the middle star of the Bear’s tail would be equal in appearance to the range described above on the supposition that the star is no further from us than the nearest known star (Alpha Centauri). That is, such a comet, if it could be seen and watched during a period of about 122,000 years, would seem to recede from the star to a distance equal to about one-fourth the space separating it from its close companion, and then to return to the point of nearest approach to its ruling sun.
Such are the immensities of star-strewn space! The journey of a comet receding from the sun with inconceivable velocity during hundreds of thousands of years carries it but so small a distance from him compared with the distance of the nearest star as scarcely to change the appearance of the celestial landscape; and yet the distances separating the sun from the nearest of his fellow suns are but as hairbreadths to leagues when compared with the proportions of the scheme of suns to which he belongs. These distances, though so mighty that by comparison with them the inconceivable dimensions of our own earth sink into utter nothingness, do not bring us even to the threshold of the outermost court of that region of space to which the scrutiny of our telescopes extends. Yet the whole of that region is but an atom in the infinity of space.
FOOTNOTES:
[2] It might be suggested that the appearance of this blazing comet among the stars drove the more superstitious of the Israelites at that time to the worship of star-gods, as we read how, during the Judgeship of Jair, they “served Baalim and Ashtaroth, and the gods of Syria and the gods of Moab, and the gods of the Philistines, and forsook the Lord and served not Him.” To a people like the Jews, who seem to have been in continual danger of returning to the Sabaistic worship of their Chaldean ancestors, the appearance of a blazing comet may have been a frequent occasion of backsliding.
EXTENT OF THE SIDEREAL HEAVENS.—Sir Robert S. Ball
Of all the discoveries that have ever been made in science there are two which especially baffle our powers of comprehension. They lie at the opposite extremes of nature. One relates to objects which are infinitely small, the other relates to objects which are almost infinitely great. The microscope teaches us that there are animals so minute that if a thousand of them were ranged abreast they would easily swim without being thrown out of line through the eye of the finest cambric needle. Each of those minute creatures is a highly organized number of particles, capable of moving about, of finding and devouring its food, and of behaving in all other respects as becomes an animal as distinguished from an unorganized piece of matter. The mind is capable of realizing the structure of these little creatures, and of fully appreciating their marvelous adaptation to the life they are destined to lead. If these animals excite our astonishment by reason of their extreme minuteness, there is an appeal made to conceptions of an entirely different character when we learn the lessons which the telescope teaches. As the microscope reveals the excessively minute, so does the telescope disclose the sublimely great. In each case myriads of objects are submitted to our astonished view, but while the microscope brings before us creatures of which countless millions could swim about freely in a thimbleful of water, the telescope conducts our vision to uncounted legions of stars, many of them millions of times larger than the earth.
The grandest truth in the whole of nature is conveyed in that first lesson in astronomy which answers the question: What are the stars? This is a question that a child will ask, and I have heard of a child’s pretty idea that the stars were little holes in the sky to let the glory of heaven shine through. The philosopher will replace this explanation by another hardly less poetical, which will enable us to form some more adequate notion of the real magnificence of the universe. Each star that we see is, it is true, only a glittering little point of light, but that is merely because we are a long way from it. An electric light which will dazzle your eye when quite close will be reduced to an agreeable illumination if it is at a little distance, will become a faint light a mile away, and at no great distance will become altogether invisible. We must remember that out in space there is plenty of room—there are no bounds; and therefore when we see light glistening in the far distant depths we can not at once conclude that the light is a faint one because it appears to us to be faint. It may be that the light is only faint because it comes from such a tremendous distance. In fact, the brightest light conceivable could be reduced to the insignificance of a small star if only it were removed sufficiently far.
The most intense light we know of comes, of course, from the light which rules by day, from our sun himself. The sun pours his unrivaled beams around us in all directions with prodigal abundance, notwithstanding his enormous distance of ninety-three millions of miles. Let me describe an experiment with respect to our sun, an experiment, it is needless to say, which could never be performed, but the results to which it leads us are none the less certain. Astronomers have demonstrated them in many other ways.
Suppose that the sun were gradually to be moved away further and further into space; suppose that by this time to-morrow the great luminary should be twice as far as it is now, and the next day should be three times as far, and the day after that four times, and so on until in a year’s time we should find that the sun was 365 times the distance from us that it is at present. Let us now trace the changes which we should see in the brilliancy of our orb of day. When he had reached double his distance from us, we should find that the light had decreased to a quarter of its present amount, and the heat which we derived from his beams would have decreased in the same proportion. In ten days we should find that the light had become so feeble as to be only one-hundredth part of that which we enjoy now. The apparent size of the sun would also be steadily decreasing, for as the distance of a body increases its apparent dimensions diminish. Sometimes the diminution of apparent size with distance is well illustrated on a clock tower. You would hardly believe that the hands and face of a clock like that at Westminster were so large until you happen to see a man cleaning or repairing it, when he appears a mere pigmy in comparison with the mighty dial which points out the hours. In a similar way with every increase of distance, the apparent size of the sun would decline, and in the lapse of a year the sunlight would be reduced to a feeble twilight. The sun itself would remain visible for many years, even if it were steadily moving away, though its lustre would continually decline, and its size would continually diminish, until at last it would have shrunk to the insignificance of a small point of light, still visible as a glittering object, but too minute to enable any definite form to be perceived.