Before entering upon such an examination, however, it seems necessary to go somewhat more into detail in illustration of the nature of this hypothesis. It may conveniently be described under the heads of _cosmogony_, which attempts to account for the origin of the world; _zoögony_, which explains the origin of animals; and _zoönomy_, which describes the laws of animal life.[17]
The cosmogony of this theory is embraced in what is denominated the nebular hypothesis, propounded by the eminent mathematician La Place. He supposes that, originally, the whole solar system constituted only one vast mass of nebulous matter, being expanded into the thinnest vapor and gas by heat, and more than filling the space at present occupied by the planets. This vapor, he still further supposes, had a revolution from west to east on an axis. As the heat diminished by radiation, the nebulous matter must condense, and consequently the velocity of rotation must increase, and an exterior zone of vapor might be detached; since the central attraction might not be able to overcome the increased centrifugal force. This ring of vapor might sometimes retain its original form, as in the case of Saturn's ring; but the tendency would be, in general, to divide into several masses, which, by coalescing again, would form a single mass, having a revolution about the sun, and on its axis. This would constitute a planet in a state of vapor; and by the detachment of successive rings might all the planets be produced. As they went on contracting, by the same law, satellites might be formed to each; and the ultimate result would be solid planets and satellites, revolving around the sun in nearly the same plane, and in the same direction, and also on their axes.
Although this hypothesis has been regarded with favor by many philosophers, who were Theists, and even Christians, yet the object of La Place in proposing it was to sustain atheism. Sir Isaac Newton had expressed the conviction that "the admirable arrangement of the solar system cannot but be the work of an intelligent and most powerful Being." La Place declared that, in this statement, Newton "had deviated from the method of true philosophy," and brought forward these views to sustain his declaration. Whether they do sustain it, will be considered in another place. But since it is one of those modes in which men have attempted to account for the universe without a Deity, it is a proper subject of examination in this lecture, in which we are inquiring whether law alone will account for the creation and sustentation of the universe.