BY J. W. SUTTON. 87 



was supposed that somewhere in the?e outskirts of the spectrum, 

 the " X " rays would be found if they are associated with Ught 

 at ah. Shadowgraphs were produced years ago, Mr. Sutton 

 remarked, in the early stages of electric lighting, by placing 

 sensitive plates protected from ordinary light in the magnetic 

 field in the dynamo armature, and it had also been noticed that 

 some persons emitted phosphorescence from their fingers 

 sufficient to imprint itself upon a sensitive plate. But still,, 

 notwithstanding all that was known previously, the discovery by 

 Professor Rontgen was accidental, and it was made while he was 

 experimentmg with a Crookes tube in the presence of a packet 

 of sensitive plates. The plates were fogged, that is they 

 had been acted upon by some kind of light other than ordinary, 

 but to an experienced experimenter like the professor, the 

 cause was apparent, and thus the world was startled by a 

 wonderful discovery. He would be a bold man, indeed, wha 

 would predict the developments that are likely to take place 

 within the next two or three years. 



Mr. Sutton proceeded to explain the apparatus he had pro- 

 vided in illustration of his remarks. Having briefly referred to 

 the electric battery and the large induction coil by which the 

 necessary current was provided to illuminate the Crookes focus 

 tube, he called the attention of his audience to .an ordinary 

 vacuum or Geissler tube. He passed the electric current through 

 this tube, which was a large three-bulb one, and it was immedi- 

 ately filled with the well known phosphorescent glow. Doubtless, 

 said Mr. Sutton, there were " X " rays emanating from the tube, 

 but they were so diflused as to be of no efiect. In Crookes tube, 

 through which the current was next passed, a more complete 

 vacuum had been obtained and other improvements made. It 

 was while experimenting with one of these tubes that Professor 

 Rontgen stumbled across the famous " X " rays. The next step 

 was to improve the vacuum tube still further by obtaining a more 

 complete vacuum and introducing an arrangement of aluminium 

 and platinum discs by means of which the " X " rays were 

 focused. Next Mr. Sutton introduced his audience to the subject 

 of fluorescent screens. Fluorescence was a peculiar property 

 possessed by some substances, and to it in 1852 Professor Stokes 

 called attention. Balmain's luminous paint was a familiar 



