AIM AND PROGRESS OF PHYSICAL SCIENCE. 327 



ceived as a causal connection the moment we recognise that it is 

 independent of our thought and will. 



If then we direct our inquiry to the progress of physical 

 science as a whole, we shall have to judge of it by the measure 

 in which the recognition and knowledge of a causative connec- 

 tion embracing all natural phenomena has advanced. 



On looking back over the history of our sciences, the first 

 great example we find of the subjugation of a wide mass of facts 

 to a comprehensive law occurred in the case of theoretical me- 

 chanics, the fundamental conception of which was first clearly 

 propounded by Galileo. The question then was to find the 

 general propositions that to us now appear so self-evident, that 

 all substance is inert, and that the magnitude of force is to be 

 measured not by its velocity, but by changes in it. At first the 

 operation of a continually acting force could only be represented 

 as a series of small impacts. It was not till Leibnitz and Newton, 

 by the discovery of the differential calculus, had dispelled the 

 ancient darkness which enveloped the conception of the infinite, 

 and had clearly established the conception of the Continuous and 

 of continuous change, that a full and productive application of 

 the newly-found mechanical conceptions made any progress. The 

 most singular and most splendid instance of such an application 

 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 gravitation, 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 in- 

 vestigation, partly by its practical utility in navigation and 

 geodesy, and the many industrial and social interests arising 

 from them. 



