Page:A Treatise on Geology, volume 1.djvu/48

 32, like the nebulæ and comets; speculations which, however, can only be changed into probable inferences by the progress of modern astronomy. For the examination of these obscure bodies, most powerful telescopes are required. The observations of Lord Rosse have resolved so many of the nebulæ into small stars, that it is doubtful whether any of them can be safely appealed to in illustration of the supposed process of condensation and arrangement.

The progress yet made in chemical philosophy is perhaps not such as to enable us to discover the single condition on which the elements, now so firmly united, could exist separately, in a free gaseous expansion; yet, since chemical combinations are known to be subject to temperature, liable to be altered and even reversed with a change of this condition, may we not suggest, as the least improbable view, that the nebulous condition of a planet may be due to intense heat existing among its particles; that, in fact, a great heat prevents their combination, and maintains them all together in a gaseous state, as it is known to be capable of doing, for most of them singly, and several of them together? In mixed or combined gases metallic matters are frequently present (as arseniuretted hydrogen), and the atmosphere of our planet is believed by several philosophers to contain so large a proportion of the substances existing in the superficial parts of the globe, as to give origin to the meteoric stones.