78 



POPULAR SCIENCE MONTHLY 



interest by its application to dry-plate photography. When we re- 

 turn to the classical investigation of Lenard mentioned in the be- 

 ginning of this article, we are impressed by an apparently crucial 



A 



RoNTGEN Picture of a Hand after Lengthened Exposube. 

 From The New York Medical Jourual. 



experiment which he describes in regard to the existence of an 

 ether. He caused the cathode beam to pass out of his high vacua 

 through an aluminum window into another tube about three feet 



