30 TROWBRIDGE. 



A short article b\' Professor Magie, describing a similar con- 

 trivance, appeared in The Medical Ncivs^ of February i 5th. It 

 ran thus : " A sheet of black paper coated with platinum-bari- 

 cyanide, is placed with the coated side inward across the end of 

 a tube or box, into which the observer looks, and which is so 

 fitted to the face or shielded b\' cloths that the phosphorescent 

 substance and the eyes are protected from all extraneous light." 

 " If the tube be then directed towards the Rontgen rays, the 

 phosphorescent paper in the tube glows and the shadows of 

 objects interposed between it and the Crookes tube appear upon 

 it." Professor Magie subsequently suggested that the name of 

 "skiascope" (an instrument to show shadows) be given to the 

 apparatus. 



About March 20th, or a little over a month after the publica- 

 tion of Professor Magic's article in The Medical Xcivs, the Edi- 

 son fluoroscope appeared. It was essentially the same instru- 

 ment as that described in TJie Medical Nezus, except, that the 

 fluorescent substance, used by Mr. Edison to coat the screen, 

 was tungstate of calcium, which had been adopted because it 

 was believed by him to have greater fluorescent properties than 

 the barium platino-cyanide, and that it was provided with a bi- 

 nocular eye-protector, made to fit close to the face and shut out 

 all light from entering the apparatus at that end ; thus allow- 

 ing both'e}'es to be used to observe the screen. The instrument 

 was furthermore made in a convenient form, and one which was 

 considered desirable for commercial uses. The "fluoroscope" 

 or "skiascope" is very valuable for the observation of Rontgen 

 ray shadows, and has already been of considerable assistance in 

 a number of surgical operations, but it can only be used for ap- 

 proximate tests in scientific research, and is entirely unfitted for 

 certain investigations, for reasons which will be demonstrated 

 below. 



Although in the greater number of investigations with Ront- 

 gen rays the photographic negative should be used in order 

 to obtain the most satisfactory results, there are a number of 

 important experiments relating to the various phenomena of 

 Crookes tubes which must be conducted by other methods. 



