38 PHYSICAL RESEARCH 



are leading to results of very different character 

 but of equal importance. 



So also we might take the history of the photo- 

 graphic plate through all its stages, which would 

 bring into our view an entirely different line of 

 advance, and force us to recognise all that chemistry 

 had to give before Rontgen's experiment could be 

 done. And we might take the electric battery and 

 allow our minds to recall the numbers who have 

 studied it during the last century, and the enormous 

 extent of its application. 



The experiment then, when it is considered in 

 detail, illustrates all the more fully the principles 

 stated at the beginning of this chapter. There is 

 a sequence of events which cannot be reversed. 

 In that sequence discovery follows on discovery; 

 and science must be pure in the sense that each 

 step is necessarily free from any knowledge of 

 what advantage may be made of it. The step is 

 made, not because this or that consequence will 

 be profitable, but because it is the next step on 

 the only way. Science cannot be applied until 

 there is science to apply, and science must begin 

 as pure science. That is why it is impossible to 

 conceive of the development of applied science as 

 apart from pure. It is not even possible to say 

 that now at this moment there is enough pure 

 science, and we may henceforth devote ourselves 

 to applying what we have. Such present neglect 

 must only lead to future sterility. The very experi- 



