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METHODS IN MODERN PHYSICAL ASTRNOMY.

yellow ones. In this manner the spectroscope may help us to estimate in some degree the age of a sun, and measure the length of the career which it has already accomplished.

While studies of this kind were going on in France, spectrum analysis was receiving magnificent developments in England, more in the line which its authors had indicated. Messrs. Miller and Huggins entered upon the study of the stars, and found in all of them which they examined the solar elements in various combinations. This discovery had an immense philosophical bearing, for it proved that the matter forming the solar and the stellar world is obtained from the same elements. It was a demonstration of the material unity of the universe. The study was prosecuted still further. There are stars which we regard as situated on the confines of the visible universe, the light of which is so weakened by the immense journey it has to make to reach us that they appear only as feeble glows. Mr. Huggins succeeded in analyzing some of them, and showed that there exists a whole class of nebulæ which are really unresolvable into stars, and are formed of incandescent gases, among which hydrogen, which thus seems to be the principal element in the composition of the universe, is the most prominent.

So the whole visible universe—not only our central star and the planets of our family, but those stars, too, which are so far off that our most powerful telescopes can not give them a sensible diameter, and those nebulæ which only make a weak glow in our instruments—is reached by our chemistry, seized by our analysis, and made to furnish the proof that all matter is one, and that these stars are made of the same stuff as we. More, still, than this: at those great distances, and in the presence of the vague and indefinite forms of the nebulæ, it would not be possible to study precise movements and discover whether the great law of gravitation reigns in such remote regions. Chemistry here comes to the aid of mechanics, and we may say boldly that that matter, which is identical with ours, is subject, like it, to the laws of gravitation. Certainly, when Newton decomposed a beam of white light, and laid the first basis of the theory of the spectrum, he had not the slightest suspicion that his law of gravitation would, at a later period, find in it wings to carry it into regions where all measurement ceases and all calculation is powerless.

Spectrum analysis, after having in this manner, in a few years, gone through the universe and reaped the magnificent harvest I have just described, now returns to the sun, the point whence it departed, to take advantage of the opportunity afforded by eclipses. These phenomena, it is well known, exhibit a collection of magnificent spectacles of an extraordinary character, which had heretofore remained unexplained. Those rosy-colored protuberances of strange forms which surround the dark limb of the moon, that magnificent luminous corona, those radiances in the form of a glory and extending to enormous dis-