The History and Properties of the Rontgen Rays. 57 



forming the cathode. In the centre of the bulb facing the 

 cathode was a square piece of platinum foil forming the anode. 

 These were connected with the coil by platinum wires fused 

 into the glass. The tube was well exhausted ; only about 

 I'loooo of the original air remained. When the coil was 

 working the negative rays passed out normally from the 

 cathode, and were focussed upon the platinum anode, which 

 became an intensely strong source of "Rontgen rays. These 

 rays then travelled out into space, just as light ravs did from a 

 lamp. (i) Rontgen rays were invisible. The tube was 

 enclosed in a wooden box, and giving rays out freely, and yet 

 they could see nothing. (2) Thev made certain substances 

 luminous when they fell upon them. The best substance was 

 barium-platino-cyanide. Mr. Finnegan produced a paper screen, 

 coated on one side with this salt. When the X rays struck it 

 the screen was quite bright, almost as bright as if it were 

 illuminated by a candle. (3) Many substances transparent to 

 ordinary light were quite opaque to X rays When a glass 

 bottle containing water was held between the Rontgen tube and 

 the screen, a very dark shadow was cast on the screen. On the 

 other hand, many substances quite opaque to ordinary light 

 were transparent to X rays. This wooden box, containing 

 cotton wool allowed most of the rays to pass through; the nails 

 which fastened it, and an iron bicycle wrench' in it, were 

 opaque, and cast a deep shadow. Flesh was much more 

 transparent than bone, and so, if he held his hand in front of 

 the Rontgen lamp, there was a faint shadow of the flesh and a 

 deep shadow of the bone. With this tube and coil could be 

 easily seen the shadow of the ribs and the motion of the 

 diaphragm. After long and frequent exposures the skin gets 

 irritated, affected with something like acute sun-burning. The 

 nails might even be shed. (4) X rays acted on an ordinary 

 photographic dry plate. The pictures they saw were produced 

 by wrapping a plate in black paper. Place upon it the object, 

 and expose it to the X rays a few minutes, then develope it in 

 the usual way and they had a picture, the difference in density 



