n6 POPULAR SCIENCE MONTHLY. 



possible. Doubtless the labor would prove irksome and monotonous, 

 but the reward would be sure. In five years, more would be done 

 toward rendering chemistry an exact science than can be accom- 

 plished in a century by means of chemical investigations at present 

 most in vogue." Chemists engaging in work of this kind would 

 have to make sacrifices, for it would offer little promise of sensa- 

 tional reputations to be gained through dazzling discoveries, and 

 would have to look to the ultimate glory of the science for their 

 chief reward. 



Professor Clarke has not omitted to practice what he thus 

 preached; and while he has not failed to win honors in other fields 

 of the science, has made it the chief work of his scientific life to 

 advance toward solution one of the physical problems of chemistry 

 indicated above. He has taken as his special field of research the 

 " constants," and of these, the one which is perhaps the most funda- 

 mental of all, the revision of the atomic weights — not by experi- 

 ments of his own so much as by comparison and criticism of the 

 work of all who have undertaken the task, eliminating errors and 

 finding from the sum of the whole what is the nearest deducible 

 approach to accuracy. In 1872 he sent to the Smithsonian Institu- 

 tion a compilation entitled A Table of Specific Gravities, Boiling 

 Points, and Melting Points for Solids and Liquids. This was ac- 

 cepted by Prof. Joseph Henry, who made it the first publication of 

 a projected series to be called The Constants of Nature. To this 

 series Professor Clarke has since contributed Tables of Specific 

 Heats, of Expansions, and a Recalculation of the Atomic Weights. 

 A new edition of the Specific Gravities was issued in 1886, and a 

 second edition of the Atomic Weights in 1897. For the past five 

 years Professor Clarke has contributed an annual report on atomic- 

 weight determinations to the Journal of the American Chemical 

 Society, giving each year a consistent table of values brought thor- 

 oughly down to date. These tables are now used in all parts of the 

 world as standards for reference. 



As chemist of the United States Geological Survey, Professor 

 Clarke has published ten official bulletins of work done in the 

 laboratory under his charge, of which Bulletin 125, The Constitu- 

 tion of the Silicates, and Bulletin 148, Analyses of Rocks and 

 Analytical Methods, by F. W. Clarke and W. F. Hillebrand jointly, 

 are the most important. Other works are: Weights, Measures, and 

 Money of All Nations, 1875; The Elements of Chemistry, a school 

 text-book, 1884; and a Report on the Teaching of Chemistry and 

 Physics in the United States, published by the United States Bureau 

 of Education in 1881. 



A paper published by him in the Popular Science Monthly for 



