Page:Popular Science Monthly Volume 18.djvu/878

858 conditions of temperature and pressure, obtained the sulphurets, oxides, and metallic salts he sought, with the bed-rock that held them. M. Daubrée has reproduced cassiterite, and several of the minerals that are found with it, by subjecting water and the right oxides to the action of chloric and fluoric vapors. MM. Fouqué and Michel Levy, also following the indications of geological observation, have obtained the minerals of volcanic rocks in crystals, not only as isolated minerals, but also with the associations under which they form real rocks, resembling the natural rocks so closely as to deceive. Other processes have been employed, varying in their nature and operation according to the minerals which it was desired to produce, or the substances from which their production was sought. The number of minerals obtained by the different processes is so great that the mere enumeration of them all would be tedious. The most obvious and simple process is that of fusion. Some substances, among them the silicates, tend, when they cool from a liquid condition, to form amorphous glasses. Many of these, it has been found, will crystallize when heated again nearly up to the melting point. By this process of sub-fusion several of the feldspars, oxide of iron, spinel, garnet, and other minerals have been obtained. When the substance does not melt readily, or is liable to decompose before melting, the process is aided by heating it with some suitable solvent. Thus have been obtained apatite, wolfram, tungstate of lead, pyrites, boracite, and other minerals. A considerable number of minerals may be crystallized from solutions in water of different temperatures. A curious feature of this process is that it operates sometimes to render a hydrate anhydrous. At other times the water may serve as a base to remove a portion of acid. It has been noticed also in this process that the crystals may be made larger by exposing them to repeated variations of temperature. Some minerals have been obtained from volatile solvents by vaporizing the solvents, when the minerals would be precipitated. Another process is by the action of two substances upon each other with or without the addition of electrical excitement, as when the oxide of copper is produced by the action of the solution of sulphate of copper and galena; another is by the reaction of vapors and gases on other bodies of similar nature or on solids—a process in which chlorine and the members of its group may play an important part.

M. Faye's Theory of the Solar System.—M. Faye, having pointed out in a former paper certain particulars in which the nebular hypothesis of Laplace fails to account for the movements of the planets, has published a second paper propounding a theory by which the retrograde movements of a part of the planets may be reconciled with the direct motions of the other planets, as results of the same laws. The theory of Laplace presupposes the existence of an immense degree of heat expanding the mass of the sun and its atmosphere to the extreme limits of the solar system, and a contraction by cooling, in the course of which planetary rings were thrown off by an excess of centrifugal force. M. Faye objects to the hypothesis of great heat as one of which there is no evidence; moreover, if the heat had existed and contraction had taken place by cooling, the outer atmosphere of the sun would have participated in the cooling and contraction so fully that it would have adhered to the mass, and no rings would have been thrown off. The new theory which he proposes in the stead of that of Laplace is based on the observation of the nebulae, bodies which astronomers have often regarded as the points of departure for evolutions very different from those pictured by Laplace for evolutions tending to formations of the most varied character, as simple, double, triple, and quadruple suns, and globular aggregations of minute suns numbered by thousands. Would it not be natural, he asks, to accept the suggestion of these facts, the more so since our system belongs to the most common type—that of a nebula at first vague, then undergoing a central condensation, absorbing itself gradually and regularly into a nebulous star and finally into a solitary sun? Under this view, heat would no longer have to be invoked arbitrarily as an external agent; we would, on the other hand, see it gradually developed in certain points of the nebula, as the proper result of the energy