analysis, also, in conjunction with the study of the curious double stars (which have been more exactly recognized within the last decade and are now known by the thousand) has brought about the highly important conviction of the unity of what is to us the visible universe, and the correspondence of its elements and forces and of the laws by which the whole is governed. In the same science, the progressive improvement of the astronomical perspectives and giant telescopes has furthermore made possible a much more extended insight into the infinite depths of the universe, and, supported by the art of photography, has made known the existence of new stars—among them fixed stars or suns—a hundred or a thousand times as great as our sun. Even more important is the discovery in the same manner of those strangely rotating primeval nebulæ, composed of incandescent gases, which are nothing else than stellar systems in a state of formation. Observation of these has raised to almost a certainty the theory of Kant and Laplace as to the origin of those systems. One of the strangest of those systems is the great nebula in Andromeda which can be seen with the naked eye. The photographic image of this object, obtained by the English astronomer Dr. Roberts, by means of a twenty-inch reflecting telescope, exhibits distinctly the various phases of its development. The improved telescopes of the present time have furthermore provided us with such an intimate knowledge of the constitution of the surface of our moon that it is now better known than some parts of the surface of the earth—as in the interior of the great continents of Africa, Australia, and America. Similar information, though to be taken with reserve, was obtained from the remarkable phenomena observed on the surface of the planet Mars. The interpretation of these features has not been thus far absolutely settled, but in the opinion of eminent astronomers they indicate the presence on that planet of thinking beings. To the present century also belongs the somewhat older discovery of the planet Neptune, which was made in such a wonderful way by Leverrier and Galle in 1846. This discovery must be regarded as one of the greatest triumphs of astronomical science, since it was the fruit of a demonstration by mathematical calculations of the existence of a heavenly body, while the actual finding and identification of it were achieved afterward by means of the telescope. In like manner, by the application of the laws of gravitation to the peculiar movements of the magnificent fixed star Sirius (the Dog Star of the ancients), its character as a double star was recognized twenty years before Clark, in Boston, discovered, on January 31, 1862, its companion, and by this discovery furnished the weightiest argument in support of the universality of the law of mass attraction.
