662 THE POPULAR SCIENCE MONTHLY. 



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 at- 

 tempts 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 pub- 

 lished 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 in- 

 stances 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 acknowl- 

 edged 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 unfavor- 

 able 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 Geol- 

 ogy," ' " 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 ; 



1 Lyell, b. iv., p. 328, fourth edition. 



s " History of the Iuduetive Sciences," b. viii., sec. 2, edition of 1857. 



