Page:Popular Science Monthly Volume 39.djvu/359

Rh Prof. Lockyer made a number of careful experiments on the spectra of fragments of "undoubted meteorites" obtained from the British Museum. These were examined at various temperatures, varying from that of the "Bunsen burner" to that of the electric spark with Leyden jar. He finds that, at the lowest temperature, the most prominent line of magnesium is a fluting near the wave-length 500. I may here explain that by the term "fluting" is meant a series of bright lines, usually three, which are sharp on the side toward the red end of the spectrum, but have a hazy fringe on the blue side. These "fringes," when examined with a powerful spectroscope, are seen to be composed of a number of fine lines very close together. In the case of "iron" meteorites, the lines of manganese are the first to make their appearance, owing to its volatility being greater than that of iron.

Lockyer finds that only the lowest temperature lines of magnesium, sodium, iron, chromium, manganese, strontium, calcium, barium, potassium, bismuth,-and nickel are seen in the spectra of the meteorites.

He shows the probable identity of origin of luminous meteors and falling stars with meteorites, and also that comets are probably composed of meteoric stones. Discussing the observations of the aurora, he attempts to prove that the phenomenon is due to meteoric dust in the "higher reaches" of our atmosphere, and that the characteristic line seen in the auroral spectrum is identical with the brightest fluting of manganese. Dr. Huggins's researches, however, show that this coincidence does not exist; and some recent experiments made by Messrs. Liveing and Dewar with an electric discharge passing through dust show that the dust does not act like a gas, and does not become luminous like the aurora, but that, on the contrary, the electric current drives it out of its path.

Lockyer next proceeds to discuss the appearances presented by comets,-and the character of the spectra they show at different distances from the sun, and concludes that their spectra very much resemble the spectra of meteorites seen under similar conditions of temperature. He considers that the light of comets is chiefly due to collisions between the component meteorites, and that the observed transparency of comets may be explained by supposing the meteorites to be small, and separated by considerable intervals. A portion of the light of comets, he thinks, may be produced by collisions between the cometic swarm and other swarms existing in space; and the recorded sudden increase of light in the Pons-Brooks comet of 1883, and the Sawerthal comet of 1888, seems certainly in favor of this idea.

Lockyer holds the view that both shooting-stars and comets did not originate within the solar system, but are of cosmical