RONTGEN'S WORK 35 



Before Crookes, there were Hittorf, Geisler, Max- 

 well, De la Rue and many others back to Faraday 

 and beyond, who had studied with interest the 

 electric discharge. When Rontgen did his famous 

 experiments he was but the last of a long line of 

 investigators to each and all of whom is due credit 

 for labour which led to this success. It is important 

 to observe that no one had any inkling of the 

 result ; nor could see more than the next step ahead. 

 Never was any experiment performed for the sake 

 of making a particular application, but in all cases 

 each advance was directed along the line disclosed 

 from the vantage point gained by the efforts just 

 made. 



Consider again the tools which Rontgen pos- 

 sessed. The main pieces of apparatus were the 

 exhausted bulb, the sparking coil, the battery for 

 working the coil, and the photographic plate. The 

 exhausted bulb was simply a glass envelope from 

 which air had been removed until perhaps a 

 millionth remained. The operation was rendered 

 possible by improvements in air pumps, for which 

 Sir William Crookes was mainly responsible. His 

 own experiments were made possible by the high 

 vacua which he succeeded in obtaining. It is to 

 be observed that he laboured to make these im- 

 provements, not in order to carry out his brilliant 

 experiments on electric discharge, but because he 

 wanted to make a high vacuum with which to 

 carry out weighings necessary to a determination 



