FLUOROSCOPIC SCREENS. 



41 



The Edison fluoroscope has been used mainly to obtain an 

 actual vision of the silhouette shadows cast by objects which 

 the Rontgen rays do not readily penetrate, such as the bones of 

 the human skeleton and metallic objects. In Figure 14, A rep- 

 resents a wooden box about 28 centimeters long, shaped as in 



A 

 \ 



C 

 \ 



\ 



\ 



\ 



\ 



X 



Fig. 13. Skiascope devised by Professor W. F. Magie. 



the cut, and open at the small end at B, where there is a binoc- 

 ular eye-protector of patent leather, which is made to fit closely 

 about the eyes, so as to exclude all light from the sides, but al- 

 lowing the observer to look into the box. At C, in the large 

 end of the box A, is a screen of cardboard coated on the in- 

 side with a fluorescent substance. The screens were at first 

 made of tungstate of calcium, but now barium platino-cyanide 

 is the material generally used. The apparatus is also provided 

 with a handle. If it is desired that the shadow of the bones of 

 the human hand shall be seen, the instrument is used as fol- 

 lows : The fluoroscope is held to the eyes with the screen end 

 placed before a Crookes tube emitting strong Rontgen rays. 

 The screen immediately becomes luminous, because the fluor- 

 escent substance thereon converts the energy falling on it in 

 the form of X-rays, into the rays of ordinary light. 



The hand is then interposed between the fluoroscope and the 



