II THE PROGRESS OF SCIENCE 73 



with rapidity and precision. 1 A large proportion 

 of these compounds contain not more than three 

 or four .elements, of which carbon is the chief; but 

 their number is very great, and the diversity of 

 their physical and chemical properties is astonish- 

 ing. The ascertainment of the proportion of each 

 element in these compounds affords little or no 

 help towards accounting for their diversities; 

 widely different bodies being often very similar, or 

 even identical, in that respect. And, in the last 

 case, that of isomcric compounds, the appeal to 

 diversity of arrangement of the identical com- 

 ponent units was the only obvious way out of the 

 difficulty. Here, again, hypothesis proved to be of 

 great value ; not only was the search for evidence 

 of diversity of molecular structure successful, but 

 the study of the process of taking to pieces led to 

 the discovery of the way to put together ; and vast 

 numbers of compounds, some of them previously 

 known only as products of the living economy, 

 have thus been artificially constructed. Chemical 

 work, at the present day, is, to a large extent, 

 synthetic or creative that is to say, the chemist 

 determines, theoretically, that certain non-existent 

 compounds ought to be producible, and he proceeds 

 to produce them. 



It is largely because the chemical theory and 



1 "At present, more organic analyses are made in a single day 

 than were accomplished before Liebig's time in a whole year," 

 Hofmann, Faraday Lecture, p. 46, 



