various experiments it was demonstrated that, every form of motion being convertible into heat, the amount of heat generated by a given motion may be calculated. If the particles of a vast vaporous mass were brought into collision from the effect of their mutual attraction, intense heat would ensue. The amount of caloric generated by the arrest of the converging motion of a nebula like the solar system would be sufficient to fuse the whole into one mass and store up a reserve of solar heat for millions of years.
Such, then, is the most probable conjecture respecting the origin of our system. We now turn to consider the grounds on which attempts have been made to fix the probable date of its creation. It will be convenient to examine the views of modern geologists on the subject, and the objections, based on recent results of physical science, which natural philosophers have adduced against their speculations.
The great representative, in late years, of British geology, is the late Sir Charles Lyell. But a few months before his death he published the new edition of his "Principles of Geology," the title of which we have placed at the head of this paper. While he lived he bestowed upon the correction of his works unwearied labor. Edition after edition was called for, and in each whole passages—sometimes whole chapters—were remodeled. A quotation from one of the earlier editions may not improbably be searched for in vain in those which subsequently left his hands; and there are not wanting instances in which an opinion, contested by competent adversaries, was quietly dropped without any formal parade. His judgment was always open to appeal, and his clear and manly intellect acknowledged no finality in matters of opinion; therefore, on matters which we know to have been brought before him, with their accompanying evidence, we may consider ourselves as possessing his final verdict. It would not be fair when quoting, as we must do, comments unfavorable to some of the conclusions at which Sir Charles Lyell arrived, to refrain from acknowledging the care with which his opinions were formed, and the candor with which they were surrendered if ever his better judgment considered them untenable. For instance, as head of the Uniformitarian school, he was exceedingly anxious that the evidence for his favorite doctrine should be duly and impartially weighed. With this view he advocated, in his "Principles of Geology,"[1] "an earnest and patient endeavor to reconcile the indications of former change with the evidences of gradual mutations now in progress."
Upon this remark Dr. Whewell[2] fell with merciless severity: "We know nothing," says he, "of causes; we only know effects. Why then should we make a merit of cramping our speculations by such assumptions? Whether the causes of change do act uniformly;
