Page:Popular Science Monthly Volume 39.djvu/360

346. This view of the origin of comets was held by the famous Laplace, but Kant thought they originated in the solar system; and the terrestrial origin of meteorites was advocated by Sir Robert Ball and Tschermak.

Lockyer then proceeds to discuss the probable construction of the nebula?, and concludes that they are probably swarms of meteorites; the collisions between the component meteorites producing the light emitted by these objects. He attempts to prove that the brightest line seen in the spectra of the nebulæ, "the chief nebular line" as it is called, is coincident with the edge of the magnesium fluting seen in the spectra of meteorites. The nebular line certainly lies very near this fluting, but the spectroscopic power used by Prof. Lockyer was quite insufficient to decide so delicate a question. Recent observations by Dr. Huggins, with a more powerful spectroscope, and by Mr. Keeler at the Lick Observatory, with a higher power still, have, however, shown that the chief nebular line in the spectrum of the great nebula in Orion, and in some others, does not coincide with the edge of the magnesium fluting, but falls within the fluting, toward the blue end of the spectrum.

Classifying the stars in accordance with his theory, Lockyer places some of them on the rising branch of a temperature curve, and others, including our own sun, and stars with similar spectra, on the descending or cooling branch of the curve. From an examination of the spectra he considers that the red and orange stars of Secchi's third type, which includes many variable stars, are increasing in temperature, while the still redder stars of the fourth type, of which some are variable also, are cooling bodies, and are "approaching the extinction of their light," The stars showing bright lines in their spectra, he thinks, "are nothing more than swarms of meteorites, a little more condensed than those which we know as nebulæ." He identifies some of the bright lines visible in these stars with the lines of hot carbon, but this conclusion is disputed by Dr. Huggins.

Considering the subject of the binary or revolving double stars, Lockyer considers that they are merely condensed swarms of meteorites, which had probably their origin in a single nebulous mass, or a double nebulosity. He explains the phenomena of long period variable stars by supposing one swarm to revolve round another in an elliptic orbit, the increase of light at maximum being caused by collisions between the meteorites of the swarms when they clash together at the periastron. This seems a very plausible hypothesis, and quite as probable, I think, as other theories which have been advanced to explain the phenomena presented by these interesting and mysterious objects. Bright lines have been observed by Espin in several of the most remarkable