SCIENTIFIC PROGRESS. 487 



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 extend- 

 ed 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 nebulae, composed of 

 incandescent gases, which are nothing else than stellar systems in a 

 state of formation. Observation of these has raised to almost a cer- 

 tainty 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 photo- 

 graphic image of this object, obtained by the English astronomer 

 Dr. Roberts, by means of a twenty-inch reflecting telescope, ex- 

 hibits distinctly the various phases of its development. The im- 

 proved 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 some- 

 what 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 cal- 

 culations of the existence of a heavenly body, while the actual finding 

 and identification of it were achieved afterward by means of the tele- 

 scope. 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 recog- 

 nized twenty years before Clark, in Boston, discovered, on January 

 31, 1862, its companion, and by this discovery furnished the weight- 

 iest argument in support of the universality of the law of mass 

 attraction. 



