Page:Popular Science Monthly Volume 5.djvu/560

542 The darkest parts are far from being black, however they may appear by contrast, the very "blackest" part being radiant with a light which would appear intolerable to the unshielded eye. Brown and reddish tints are occasionally seen here with the polarizing eye-piece. These, the spectroscope shows, are due to incandescent hydrogen; but a common tint, which is particularly that of the nuclei or deeper umbral shades, is a very pure, violet.

It is impossible to do more, in such an article as this, than to outline, in the briefest way, a few of the more prominent appearances of the spots and solar surface, without attempting any description of the laws which regulate their respective motions, and the emission of their light and heat, and without alluding to the numerous other topics of interest to the student. The reader will not, it may be hoped, on this account derive the impression that his attention has been invited to a description of superficial solar phenomena, merely as spectacles. In this point of view alone, certainly, we cannot contemplate them without lively wonder, but their deeper interest will lie in the light they shed on the nature of the sun itself, and the laws which govern that flow of light and heat through which alone we ourselves live and move. Experience seems to indicate that, according as these wonderful phenomena are studied with or without the spectroscope, they are assimilated more, in the observer's mind, with such terrestrial motions as those we call eruptions in the first instance, or cyclones in the second. It would be generalizing from a partial view, therefore, to present the reader with any single hypothesis at present, especially while those versed in the study find so much that, on any hypothesis, is still mysterious.



NTIL very lately, all fermentations were supposed to be produced by the spontaneous decomposition of organic matter within a fermentable liquid. It was said that on contact with air this organic matter undergoes a special change which gives it the character of leaven, and this was regarded as an agent having the power of spreading decomposing movement. It is true, brewer's yeast had long been well known; the facts of its cellular composition and its organization were familiar; but no relation was recognized between this organized condition and those phenomena of fermentation produced by yeast in saccharine liquids, such as grape-juice or the wort of 