volve, indeed, some of the most radical problems of popular government. We have been told that the price of liberty is eternal vigilance, and the truth is far more pregnant than is generally supposed. But we require to learn a still more elementary lesson, that is, what liberty is. Our common notion of slavery has come to be negroes sold at auction, and our notion of liberty has come to be the privilege of locomotion and of voting. A people with such notions of the subject will hardly be very vigilant in paying the price of liberty by strenuously resisting all encroachments upon individual rights. Therefore, every discussion which makes the subject clearer, and calls attention to considerations which are apt to be generally overlooked and forgotten, is important; and nowhere is it more important to guard against the indifference of citizens and the fallacies by which they are misled on the subject of liberty than where government is popularly administered. Mr. Spencer's future papers will probably bear much more directly upon American political problems than the present.
World-Life; or, Comparative Geology. By Alexander Winchell, LL.D., Professor of Geology and Paleontology in the University of Michigan. Chicago: S. C. Grigg's & Co. Pp. 642. Price, $2.50.
In this compact but comprehensive book Professor Winchell has made a contribution to science that was greatly needed, and he has performed his task in a manner that well comports with the grandeur of the subject. A carefully prepared book, representing the present state of knowledge on "the processes of world-formation, world-growth, and world-decadence," has been urgently needed for some years. There is, no doubt, much shallow skepticism in many minds regarding the validity of inquiries in this field, which has been relegated to the sphere of scientific romance and fanciful speculation. But sober and well-instructed minds have not shared in this feeling. Our knowledge concerning the genesis of worlds is, of course, yet very incomplete, and there is necessarily much of that divergence of opinion in relation to it which always belongs to the stage of active advancing inquiry. But there is already a great body of assured and formulated knowledge bearing upon the problem of the genesis of worlds which is not to be gainsaid, and there has been the steadily increasing necessity that this knowledge should be collated, and organized into definite scientific form. But a somewhat special preparation was required to do anything like tolerable justice to this work. The factors of the discussion are of the largest import. Celestial mechanics has long been the fundamental element of the research, and within recent years celestial chemistry has come forward as of equal importance. Nebular cosmogony and nebular evolution are now established conceptions of science, and, in working them out, the sciences of geology and astronomy are of equal significance and application. Professor Winchell refers to his task as an attempt at "laying the foundations of a science which, from one point of view, may be styled the geology of the stars, and, from another, the astronomy of the earth. It is the science of comparative geology. It is astrogeology." In regard to the present position of the nebular view, the author remarks: "Nor can it be correctly said that the general theory remains still in the status of an hypothesis. In certain points of detail opinion may still remain divided; but, when an hypothesis has stood the scrutiny of three generations, and has become all but unanimously accepted, by those prepared to form original opinions, as the real expression of a method in nature, surely, then, the time has passed when any person can advantageously illustrate his learning and sagacity by continuing to reproach the conception as 'a mere hypothesis.' If any 'mere hypothesis' ever strengthened into the condition of a scientific doctrine, assuredly we find in the scientific world today the general features of a sound nebular doctrine."
Professor Winchell's geological studies, long carried on in connection with the cosmical problems which they involve, have well