AIM AND PEOGEESS OF PHYSICAL SCIENCE. 373 



tion was in regard to the motion of the planets, and I 

 need scarcely remind you here how brilliant an example 

 astronomy has been for the development of the other 

 branches of science. In its case, by the theory of gravi- 

 tation, a vast and complex mass of facts were first 

 embraced in a single principle of great simplicity, and 

 such a reconciliation of theory and fact established as 

 has never been accomplished in any other department of 

 science, either before or since. In supplying the wants of 

 astronomy, have originated almost all the exact methods 

 of measurement as well as the principal advances made 

 in modern mathematics ; the science itself was peculiarly 

 fitted to attract the attention of the general public, partly 

 by the grandeur of the objects under investigation, partly 

 by its practical utility in navigation and geodesy, and 

 the many industrial and social interests arising from 

 them. 



Galileo began with the study of terrestrial gravity. 

 Newton extended the application, at first cautiously and 

 hesitatingly, to the moon, then boldly to all the planets. 

 And, in more recent times, we learn that these laws of the 

 common inertia and gravitation of all ponderable masses 

 hold good of the movements of the most distant double 

 stars of which the light has yet reached us. 



During the latter half of the last and the first half of the 

 present century came the great progress of chemistry 

 which conclusively solved the ancient problem of dis- 

 covering the elementary substances, a task to which so 

 much metaphysical speculation had been devoted. Reality 

 has always far exceeded even the boldest and wildest 

 speculation, and, in the place of the four primitive meta- 

 physical elements — fire, water, air, and earth — we have now 

 the sixty-five simple bodies of modern chemistry. Science 

 has shown that these elements are really indestructible, un- 

 alterable in their mass, unalterable also in their properties j 



