THE BECQUEREL RAYS FROM RADIUM. 



97 



PHOTOGRAPHIC POWER. 



In their power to take radiographs, Becquerel rays from 

 radium resemble X-rays (Fig. 27). A radiograph of a purse 



Fig. 27. Radiograph by the Curies. A pinch of radium was used at 

 a distance of a foot. Time, 1 hour. 



was taken in the dark by exposing the plate with the purse 

 upon it to the invisible Becquerel rays for one hour. It has 

 all the characteristics of an X-ray picture. 



PHOSPHORESCENCE. 



Many substances when they are exposed to Becquerel 

 rays shine in the dark that is they phosphoresce. The dia- 

 mond and the ruby shine out vividly on being held up in the 

 invisible rays emitted by a pinch of chloride of radium. So 

 do fluorspar, calcium sulphide, barium platino-cyanide, and 

 many others. So powerful is the phosphorescence caused by 

 Becquerel rays that if a tube of radium bromide be held to 

 the forehead, and the experimenter close his eyes, he will 

 still see light. The retina itself becomes phosphorescent. 



