8 THE POPULAR SCIENCE MONTHLY. 



necessary for him to consider every point with the extreme de- 

 liberation involved in framing distinct mental images of things 

 and processes which he conld not watch with the eye. It was 

 hard discipline, but he doubtless profited from it. Nature had 

 endowed him with an unusually clear head, but this enforced 

 method must have made it still clearer. One of the most notable 

 qualities of his mind was the absolute luminousness with which 

 he saw things and the relations among things. It was this quality 

 that made him so successful as an expounder of scientific truths. 

 In the course of his pondering over chemical facts which he was 

 obliged to take at second hand, it occurred to him that most of 

 the pupils in common schools who studied chemistry were practi- 

 cally no better off. It was easy enough for schools to buy text- 

 books, but difficult for them to provide laboratories and appara- 

 tus ; and it was much easier withal to find teachers who could ask 

 questions out of a book than those who could use apparatus if 

 provided. It was customary, therefore, to learn chemistry by 

 rote ; or, in other words, pupils' heads were crammed with unin- 

 telligible statements about things with queer names — such as 

 manganese or tellurium — which they had never seen, and would 

 not know if they were to see them. It occurred to Mr. Youmans 

 that, if visible processes could not be brought before pupils, at any 

 rate the fundamental conceptions of chemistry might be made 

 clear by means of diagrams. He began devising diagrams in dif- 

 ferent colors, to illustrate the diversity in the atomic weights of 

 the principal elements, and the composition of the more familiar 

 compounds. At length, by uniting his diagrams, he obtained a 

 comprehensive chart exhibiting the outlines of the whole scheme 

 of chemical combination according to the binary or dualist theory 

 then in vogue. This chart, when published, was a great success. 

 It not only facilitated the acquirement of clear ideas, but it was 

 suggestive of new ideas. It proved very popular, and kept the 

 field until the binary theory was overthrown by the modern doc- 

 trine of substitution, which does not lend itself so readily to 

 graphic treatment. 



The success of the chemical chart led to the writing of a text- 

 book of chemistry. This laborious work was completed in 1851, 

 when Mr. Youmans was thirty years old. Prof. Silliman was 

 then regarded as one of our foremost authorities in chemistry, 

 but it was at once remarked of the new book that it showed quite 

 as thorough a mastery of the whole subject of chemical combina- 

 tion as Silliman's. It was a text-book of a kind far less common 

 then than now. There was nothing dry about it. The subject 

 was presented with beautiful clearness, in a most attractive style. 

 There was a firm grasp of the philosophical principles underlying 

 chemical phenomena, and the meaning and functions of the sci- 



