Open main menu

Page:Popular Science Monthly Volume 4.djvu/533

This page has been validated.
515
THE WORLD BEFORE LIFE.

phases of growth had all been completed, and we should have passed beyond the period of organic activity. The New-Zealander would have leaped over the ruins of London, and the "last man" of Hogarth would have finished gazing upon the ruins of intellectual activity.

Fig. 2.
PSM V04 D533 Spiral nebula in canes venatici.jpg
Spiral Nebula in Canes Venatici (H., 1622).

Cosmical Analogies.—Space is full of bodies resembling our earth in all stages of its growth. The earlier stages are displayed in nebulæ, comets, and suns. The former, by the improved methods of modern investigation, are clearly shown to be in a gaseous condition, intensely heated, though not so hot as the sun, and so tenuous that the brightness of the stars behind is hardly dimmed.

There has been great progress in the study of the nebulæ. Many had been resolved into clusters of small stars by the more powerful instruments of recent manufacture, so that astronomers doubted the existence of any unresolvable forms. But, in 1866, Mr. William Huggins showed that nineteen out of the sixty nebulæ seen through the great reflecting telescope of the Earl of Rosse presented spectra exhibiting the bright bands indicative of heated luminous gas. Hence the world could no longer doubt the settlement of the question whether any of the nebulæ are composed of vapors. Prof. Young says that the majority of the nearly 8,000 known nebulæ are luminous clouds of heated gas, with minute solid and liquid particles scattered through them. In a recent number of The Popular Science Monthly, Mr. F. W. Clarke has classified these bodies, suggesting that there may be a law of development among them. The most distinct are composed of nitrogen and hydrogen, possessing a temperature beneath that of the sun. He propounds the hypothesis whether nebulæ may not pass by degrees into suns, the sixteen elements known to exist in