82 PROGRESS OF SCIENCE. 



strain the courage, that is, to defy authority, and to advise 

 men to shake off its yoke, and examine all and everything 

 for themselves ! No wonder he spent twenty-four years in 

 confinement. " In reasoning," he continues, "we commonly 

 distinguish a sophism from a demonstration by verifying the 

 conclusions through experiment," and we find him constantly 

 insisting upon the necessity of " verification " and the " futility 

 of argument." * 



C. Furthermore, " Armed," says he, " with experiment 

 and calculation, science must not be content with facts, 

 though these may have their utility ; it seeks truth ; it 

 wants to find out the laws, the causes canones, liniversales 

 regulce" f 



D. Roger was not an advocate of calculation only; he 

 was a skilful practical MATHEMATICIAN himself. He rightly 

 considered mathematics as the key of several other branches, 

 and he resolved problems of mechanics, optics, astronomy, 

 by the use of geometry. 



E. Roger was a real CHEMIST, for the way he speaks of 

 the properties of metals alone shows that he handled the 

 things he mentions. He knew that there are different kinds 

 of air (gases), and that one of them extinguishes a flame; he 

 invented the experiment of burning a candle under a bell- 

 glass to prove that the candle goes out when the air is 

 exhausted. But his most astonishing conception, perhaps, 

 was his anticipating the suggestion of our greatest modern 

 chemists, that the elements, as we know them, are evolved 

 from a primal matter (whether this be helium or protyle). He 

 says : " The elements are made out of v\y (the stuff of which 

 things are made], and every element is converted into the 

 nature of another element" (De Arte Chymia) as if indeed 

 he had a correct knowledge of the simple chemical elements, 

 and, at the same time, understood them to have been built 

 up of an earlier and simpler primordial kind of matter 

 endowed with potentialities capable of developing such 

 characters and energies, as the changeable conditions of 

 heat and pressure forced them to assume. It is of all things 



* Opus Majus, p. 336-7 ; Opus Tertium^ Cap. xin. 

 t De CahstibuS) Cap. I. 



