Page:Popular Science Monthly Volume 4.djvu/538

520 same general relation of light and heavy zones still exists, and that the deeper we descend the more abundant the proportion of the denser metals. The germ of this arrangement was undoubtedly induced in the nebulous age. The compression of the surface-elements into a quarter or half their known bulk cannot explain the great weight of the interior, for experiments indicate that a limit to the capacity of reduction of volume is soon reached. So far as we know, the reduction of bulk by pressure becomes less and less in proportion to the pressure exerted.



Some interesting observations have recently been made by Prof. Daubrée, of Paris, upon the analogy between certain terrestrial rocks and the heavy meteoric stones which occasionally fall from the sky. Some of the meteorites are nearly pure iron; others either contain grains of minerals like olivine, or consist chiefly of the olivine, with only occasional particles of iron. This latter class are silicates of magnesia and the protoxide of iron, allied to the minerals olivine or peridote, and a granular compound of anorthite and pyroxene. Patrin, so long ago as 1809, called the attention of observers to the identity between the composition of certain meteors and substances ejected from volcanoes; and, in 1858, Von Reichenbach sketched theoretically some of the conclusions just arrived at experimentally by Daubrée. Reichenbach showed that most of the mineral species found in meteors existed also in the trap called dolerite; hence he inferred that masses of material allied to the stony meteors are located deep down under the volcanoes whence the lava was derived. Daubrée has manufactured in the furnace masses apparently identical, both with the metallic and stony meteors. The latter were most successfully imitated by melting down the mineral compounds peridote, Cherzolite, hypersthene, basalt, and melaphyre. Allied to them is the dumite of New Zealand, an aggregate of olivine and chromite.