Nov. 1808.] BOTANICAL SOCIETY OF EDINBURGH 127 



sports. If we are to believe bacteriologists, microbes have 

 the most wonderful capacity for being educated. It is 

 difficult to educate a man — easy to educate a microbe. 

 It is done in every bacteriologist's laboratory. Poisonous 

 microbes are changed into harmless ones. 



As I said at the beginning of this paper, the three 

 Darwinian laws, are — Heredity, Survival of the fittest, and 

 Fortuitous variation ; but I think I ought to explain what 

 I understand by a law of Nature. 



I understand, by a law of Nature, nothing more than a 

 concise statement of the result of many observations. 



The observations of many, put in a formula by the wit 

 of one, and submitted to the criticism of all. 



I would hold that Newton did not discover the law of 

 gravitation. In reality, he invented it. For man makes 

 discoveries in the regions of percepts. He invents in the 

 region of concepts. 



Till the time of Newton, the planets did not obey the 

 law of gravitation, for that law did not exist till Newton 

 invented it to explain complex phenomena. 



We call the cycles and epicycles of Ptolemy, an invention 

 of that great astronomer, because we believe that they were 

 not a true explanation. We call the law of gravitation a 

 discovery of Newton, because we believe it was a true 

 explanation. If Newton's law of gravitation had turned 

 out to be incorrect, would that have changed it from 

 a discovery to an invention ? Both the Ptolemaic and 

 the Newtonian theories are attempted explanations of 

 phenomena, and I would call them both inventions, though 

 I believe the one to be false, and the other to be true. I 

 would keep the word, discovery, for new things perceived by 

 the senses : invention, for new things thought out by the 

 mind. Of course, those people who believe that the law of 

 gravitntion existed before tlie time of Newton, ought to con- 

 tinue to say that Newton discovered the law of gravitation. 



Darwin told us nothing about the origin of life. 



The little we know about life, we owe to Pasteur. In 

 1860, Pasteur discovered the difference between tartrates 

 and racemates, and laid down the magnificent generalisation 

 that organic matter is optically active, and inorganic matter 

 optically inactive. 



