FIRST PRINCIPLES 7 



as it could be put to practical use. Who anticipated until 

 Lister devised its practical application that the septic infec- 

 tion of wounds inflicted by the surgeon's knife could be 

 certainly prevented by performing the operation under a 

 cloud of water-vapour in which carbolic acid is supended? 

 The antiseptic property of coal-tar had long been known. 

 The chemist isolated phenol, which proved to be by far 

 the strongest germicide of all the substances which coal- 

 tar contains. Lister devised a method for investing cut 

 surfaces with an atmosphere of phenol in which it is im- 

 possible for germs to live. How far was Rontgen, when 

 he discovered by accident, truly, rather than by design 

 that cathodic rays will penetrate organic substances, from 

 foreseeing that he was equipping the surgeon with the means 

 of detecting a bullet hidden in the flesh? We have taken 

 our examples from that department of science of which the 

 applications are of the greatest use to mankind, but similar 

 illustrations are afforded by every subject of obvious prac- 

 tical utility. The discovery is made by the investigator who 

 works without weighing the question of whether his line of 

 research is more likely to benefit mankind than any other 

 line. The practical man who is on the watch for sugges- 

 tions seizes the discovery and applies it to the uses of his 

 profession. 



The superiority of pure science to applied science as a 

 field for research is even more easily proved from the op- 

 posite side. Every investigator who works in a technical 

 laboratory knows the difficulty of following a useful line of 

 research. He is constantly thrown back upon himself with 

 the conviction that only by some happy accident will he 

 discover the solution to the problem ; while at almost every 

 turn in his investigations he starts questions to which he 

 is astonished to find that no answer has yet been given, 

 problems which tempt him to forget the purpose with which 

 he set out, to leave the main road and to follow the by- 

 path, not because he believes that it will lead him to a 



