February 25, 1916] 



SCIENCE 



259 



The union of theory and practise, that is 

 the keystone of modern chemistry. Theory 

 coordinates and arranges; practise dis- 

 covers, and each one helps the other. The 

 concrete facts of science, taken only as facts, 

 form a disorderly and unmanageable mob; 

 good theory converts them into a disciplined 

 army. A thousand isolated facts are not 

 easily remembered, theory brings them all 

 under one general expression, and the diffi- 

 culty disappears. Empirical knowledge is 

 an aggregation of facts; theory combines 

 them into that systematic organization 

 M'hich we call science. Chaos gives way to 

 order. Theory, moreover, not mere specu- 

 lation, guides research into profitable paths 

 and makes practise more surely fruitful. 

 The self-styled "practical man," who af- 

 fects to despise theory, is apt to go astray, 

 and to waste his time in haphazard experi- 

 menting. The Patent Office is the grave- 

 yard of many such fruitless efforts. 



Let me illustrate my meaning by a con- 

 crete example : In theorizing upon the na- 

 ture of matter the Greek philosophers de- 

 veloped an atomic speculation which was 

 the subject of controversy, of arguments 

 pro and con, for more than twenty cen- 

 turies. It was speculation only, and it led 

 to no definite results, for it rested upon no 

 adequate basis of experiment. 



A little more than a century ago John 

 Dalton proposed an atomic theory which 

 had for its purpose the correlation and ex- 

 planation of certain established relations. 

 In this respect it differed from mere specu- 

 lation about what might or ought to be; 

 it was something more than an affair of 

 words and syllogisms, and, furthermore, it 

 assumed quantitative form. In Dalton 's 

 hands the theory led to the discovery of 

 those fundamental constants of matter 

 which we call the atomic weights, with 

 which the physical properties of the chem- 

 ical elements are intimately connected. It 



was a fruitful theory, capable of growth, 

 and for a hundred years it has been the 

 chief guide of chemical research. 



In the first place the atomic theory gave 

 us, or at least made possible, our system of 

 chemical formula, by which the composi- 

 tion of compound substances can be clearly 

 and easily expressed. A vast number of 

 individual data were thus brought into 

 order, and became manageable. With these 

 formulse equations could be constructed 

 and chemical arithmetic was born. Nearly 

 all chemical calculations, especially the cal- 

 culation of analyses, rest upon the constants 

 which Dalton discovered. As a labor-saving 

 device the atomic theory has been of enor- 

 mous value. Chemical operations are also 

 made more exact and economical by the 

 calculations which theory has rendered pos- 

 sible, and wastage is avoided. 



But this is not all. From the main stem 

 of the theory subordinate theories have 

 branched, and the theory of valency is one 

 of them. Chemical knowledge became stiU 

 more systematic and orderly, and chemists 

 were guided into profitable lines of re- 

 search. For instance, the benzene ring of 

 Kekule, a conception which had at first only 

 scientific interest, led to consequences of the 

 highest practical significance. The whole 

 development of coal-tar chemistry, for over 

 fifty years, with its discoveries of dyestuffs, 

 medicines and explosives, has been syste- 

 matically guided by Kekule 's generaliza- 

 tion. Theory and practise have worked to- 

 gether and to mutual advantage. Pure sci- 

 ence and applied science have both been 

 benefited. 



Between pure chemistry and applied 

 chemistry there is no sharp line of de- 

 marcation; both are phases of one science 

 which can not be subdivided. The differ- 

 ence between them is one of point of view, 

 of purpose, or of temperament on the part 

 of the investigator. One chemist seeks for 



