372 AIM AND PROGRESS OF PHYSICAL SCIENCE. 



individual points occurs. Its actual signification may be 

 compared with the facts and tested by them. The ab- 

 stract conception of force we thus introduce implies 

 moreover, that we did not discover this law at random, 

 that it is an essential law of phenomena. 



Our desire to comprehend natural phenomena, in other 

 words, to ascertain their laws, thus takes another form 

 of expression that is, we have to seek out the forces 

 which are the causes of the phenomena. The conformity 

 to law in nature must be conceived 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 connection 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 mechanics, 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 con- 

 ception 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 applica- 



