Page:Popular Science Monthly Volume 11.djvu/72

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62
THE POPULAR SCIENCE MONTHLY.

"The spectrum of the variable star of Corona Borealis is found to consist of two superposed spectra, the one made up of four bright lines, and the other resembling the solar spectrum, each resulting from the decomposition of a group of luminous rays independent of the light which produces the other. The continuous spectrum, furrowed with groups of dark rays, indicates the presence of a photosphere of incandescent matter, almost certainly solid or liquid, and surrounded by an atmosphere of cooler vapors, which produce by absorption the groups of darker lines. So far the constitution of this star resembles that of the sun; but it offers an additional spectrum composed of bright lines. Here, then, is a second source of special light, and this source must be a luminous gas. Furthermore, the two principal bright lines of this spectrum show that this gas consisted mainly of hydrogen; and their great brightness proves that the temperature of the luminous gas was higher than that of the photosphere. These facts, taken in connection with the suddenness of the outburst of light in the star, its immediate

Fig. 1.—Spectrum of the Variable Star in Corona Borealis. (From Huggins and Miller.)

and rapid diminution of brightness, and its decline, in the course of twelve days, from the second to the eighth magnitude, lead us to the conclusion that the star was suddenly enveloped in hydrogen-flames. Possibly it was the scene of some mighty convulsion, with disengagement of an enormous amount of liberated gas. A great portion of this gas was hydrogen, which burned on the surface of the star by combining with some other element. The light given forth by this flaming gas was characterized by the spectrum with bright lines. The spectrum of the other portion of the star's light probably showed that this terrible conflagration of gas had surcharged and rendered more vividly incandescent the solid matter of the photosphere. When the free hydrogen had been exhausted, the flame died away by degrees, the photosphere became less luminous, and the star returned to its former state. . . . We must not forget," adds Mr. Huggins, "that light, though it travels with such great velocity, nevertheless requires a certain time to come to us from the star. Hence this grand physical convulsion, though new to us, was a thing of the past as regards the star itself. In 1866 the star had already for years been in the new conditions produced by this violent catastrophe."

The solar protuberances had not as yet been directly analyzed in 1866; it was not yet known that a continuous stratum of incandescent hydrogen envelops the bright photosphere of the sun, and that the emission of this gas, in the form of irregular jets, undergoes in the sun variations, phases, which are at least so far related to the sun-spots as to be coincident with them. What mighty physical revolu-