SCIENTIFIC THOUGHT IN THE NINETEENTH CENTUEY. 897 



space belongs mainly to earlier times than ours. The Greek geometers 

 acquired approximately correct notions of the size of the earth and 

 the distance of the moon. The Copernican astronomy in the sixteenth 

 century shifted the center of the solar system from the earth to the 

 sun, and placed in truer perspective our view of the celestial spheres. 

 But, though astronomy, the oldest of the sisterhood of the sciences, 

 attained a somewhat mature development centuries ago, it has in our 

 own century thrown new light upon the subject of the vastness of the 

 universe. The discovery of Neptune has greatly increased the area of 

 the solar system; the measurement of the parallax of a few of the 

 brightest and presumably the nearest of the stars has rendered far 

 more definite our knowledge of the magnitude of the stellar universe; 

 and telescopes of higher magnifying power than had been used before 

 ha^^e resolved many clusters of small and distant stars. 



If the development of the idea of the spatial extension of the uni- 

 verse belongs mainly to an earlier period, the idea of its historic 

 extension belongs mainly to our century. It is true, indeed, that 

 Pythagoras and others of the ancient philosophers did not fail to 

 recognize indications of change in the surface of the earth. And, in 

 the beginning of the Renaissance, we find Leonardo da Vinci and others 

 insisting that the fossils discovered in excavations in the stratified 

 rocks were proof of the former existence of a sea teeming with marine 

 life where cultivated lands and populous cities had taken its place. 

 Hutton's Theory of the Earth, which in an important sense marks the 

 beginning of modern geological theorizing, appeared in the Edinburgh 

 Philosophical Transactions in 1788, but was not published as a separate 

 work till seven years later. Not till 1815 was published "William 

 Smith's geological map of England, the first example of systematic 

 stratigraphic work extended over any large area of countr3\ To the 

 beginning of our century belong also the classical and epoch-making 

 researches of Cuvier upon the fossil fauna of the Paris basin. By 

 far the larger part, therefore, of the development of geologic science, 

 with its far-reaching revelations of continental emergence and sub- 

 mergence, mountain growth and deca}^ and evolution and extinction 

 of successive faunas and floras, belongs to the nineteenth century. 

 Far on into our century extended the conflict with theological con- 

 servatism, in which the elder Silliman, James L. Kingsley. and others 

 of the early meml)ers of our acadenn^ bore an honorable part, and 

 which ended in the recognition, by the general public as well as by the 

 select circle of scientific studcMits, of an antiquity of the earth far 

 transcending the limits allowed by venerable tradition. 



To our century also belongs chiefly the development in astronomy 

 of the idea of the history of the solar system. It is, indeed, true that 

 in the conception of the nebular hypothesis Laplace, whose Theorie 

 de la Monde was published in 1796, was preceded by Kant and Sweden- 



