['9] 



knowledge to be the result of experience, thus entirely 

 upsetting the old theory of intuition. Twenty years 

 later Leibnitz published his work entitled "Theodicee," 

 in which he endeavoured to solve the difficult problem 

 of existence of evil in the world under the moral govern- 

 ment of Deity. These two rival philosophers soon 

 became the leaders of philosophic thought in their 

 respective countries ; but barely thirty years had passed 

 away before an iconoclast appeared, in the person of 

 David Hume, who cut away the ground ruthlessly from 

 beneath their feet. His " Treatise on Human Nature," 

 published in 1739, upset all the philosophical systems 

 of the past, replacing them by the great theory of causa- 

 tion, which was soon accepted by every philosopher and 

 scientist. Kant followed in 1781 with his "Critique of 

 Pure Reason," in which he submitted matter to analysis, 

 and declared it to be possessed of inherent force. 



The other sciences were also joining in the march of 

 progress. Chemistry was fast becoming a settled science ; 

 Priestley's discovery of oxygen, in 1774, had created a 

 great sensation; Cavendish shortly afterwards, in 1783, 

 discovered the constitution of water ; and Lavoisier, in 

 1789, summarised the combined researches of these two 

 chemists and himself in his " Elements of Chemistry," 

 which at once was recognised as the standard work on 

 the subject. Astronomy had, since Newton's discovery 

 of gravitation, assumed a more settled condition, but 

 was destined to further modification by the enunciation 

 of the nebular hypothesis by Laplace, who commenced 

 to publish his bulky work, "Mecanique Celeste," in 

 1799. 



The nineteenth century opened with progress, as it 

 were, on the gallop. In 1804 the first locomotive engine 

 was started in England, at the same time that the first 

 screw steamer was run at New York. It is needless to 

 enumerate all the inventions of scientific men during the 

 century, which are so well known to every one. Suffice 

 it to say that, in a marvellously short space of time, the 

 whole face of Europe has been changed. Railways 

 cross each other at ajl points, like a huge network ; 

 telegraph wires link together as one place all important 

 centres of population; public buildings arc protected 



