Page:Popular Science Monthly Volume 29.djvu/399

Rh oxygen of the air which burns, not only the charcoal, but also the silicon in the pig and a part of the iron. The black scoria which is formed in the process often contains a peridote with a base of iron, having the same chemical constitution and crystalline form as the magnesian peridote of the eruptive rocks of the earth and of the meteorites.

The simple oxidation of silicon develops an enormous quantity of heat, very much more than the combustion of carbon; a heat which is sufficient to refine the metal in the retorts of iron and steel works without the addition of carbon. Silicon, which in nature has passed wholly into the state of silicic acid, or been burned, must, at the moment of its combination with oxygen, have been the cause of an intense heating both in our own globe and in the other stars, which are also composed of silicates. But in the last, of which meteorites are the fragments, the temperature was not probably so high as in the metallurgical furnaces and the experiments we have cited. It is, in fact, very remarkable that, notwithstanding their tendency to a distinct crystallization, the silicate compounds of which the meteorites are constituted are only in the condition of very small and quite confused crystals, as if they had not passed through fusion. We might say that, rather than the long needles of ice which liquid water forms in freezing, their fine-grained texture resembles that of frost and snow, which is known to be due to the immediate passage of atmospheric aqueous vapor to the solid state.

In brief, the extreme tendency of the oxidation of silicon to produce the formation of peridote, daily proved in our laboratories and shops, is no less evidently manifested in the deeper rocks of our globe, on the one side, and in the distant stars from which the meteorites come, on the other side. Everywhere are observed the effects of an ancient and vast oxidation. In this we have a simple and experimental explanation of the ubiquity of peridote. It is the universal scoria.

As a forest shows at a glance the plant-life of all ages, the universe presents us stars in all the phases of their existence, from that of incandescent heat to obscurity, and an advanced cooling. We have also just seen that some of them are in demolition, and that their fragments fall upon others, to which they remain attached. The numerous falls of meteorites on our globe teach us that this fact, instead of being an exception, answers to an habitual régime. And the constitution of the meteoric masses teaches us with certainty that the celestial bodies whence they emanate have a chemical history quite similar to that of the interior regions of our planet.

So, while the exploration of the sky reveals to us millions of worlds beyond our solar system, our planet, small as it is, offers us an example of the changes which the stars have undergone, and an episode in the general history of the universe. The meteorites form a kind of line of union between the succession of the epochs of the earth, the object