142 THE X-RAYS. 



Most other substances are, like the air, more transmissible for X-rays 

 than for the cathode rays. 



11. Another very noteworthy difference between the behavior of the 

 cathode rays and the X-rays was exhibited in that I was unable to i)ro- 

 duce any deviation of the latter by the action of the most powerful 

 magnetic fields. The property of being subject to deviation by mag- 

 nets is, on the other hand, very characteristic of the cathode rays. 

 Hertz and Lenard have observed various kinds of cathode rays which 

 "are to be distinguished by their differences in their capacities for 

 exciting phosphorescence in their absorptibility and in their deviation 

 by the magnet," but a considerable magnetic deviation was to be observed 

 with all of them, and I do not believe that this characteristic would be 

 given up except for the most urgent reasons. 



12. According to the results of experiments particularly directed to 

 discover the source of the X-rays, it is certain that the part of the wall 

 of the discharge tube which most strongly fluoresces is the principal 

 starting point. The X-rays therefore radiate from the place where, 

 according to various observers, the cathode rays meet the glass wall. 

 If one diverts the cathode rays within the tube by a magnet, the source 

 of the X-ray is also seen to change its position so that these radiations 

 still i^roceed from the end points of the cathode rays. The X-rays 

 being undeviated by magnets can not, however, be simply cathode rays 

 passing unchanged through the glass wall. The greater density of the 

 gas outside the discharge tube can not, according to Lenard, be made 

 answerable for the great diHerence of the deviation. 



I come therefore to the results that the X-rays are not identical with 

 the cathode rays, but that they are excited by the cathode rays in the 

 glass wall of the vacuum tube. 



13. This generating action takes place not only in glass, but as I 

 observed it in apparatus with aluminum walls 2 millimeters thick, exists 

 also for this metal. Other substances will be investigated. 



14. The warrant for giving the title "rays" to the agent which pro- 

 ceeds from the wall of the discharge tube arose in part from the quite 

 regular formation of shadows appearing when more or less transmissible 

 substances are interposed between the generating apparatus and a 

 phoshorescent screen or photographic plate. I have many times 

 observed and sometimes photographed such shadow forms, in whose 

 production there lies a particular charm. I have, for example, photo- 

 graphs of the shadow of the profile of a door which separates the two 

 rooms, in one of which was the discharge apparatus, in the other the 

 photographic plate; of the shadow of the hand bones; of the shadow 

 of a wooden sj)ool wound with wire; of a set of weights in a box; of a 

 compass in which the magnetic needle is quite inclosed in metal; of 

 a piece of metal which is shown to lack homogeneity by the use of 

 X-rays, etc. 



The propagation of the X-rays in right lines is shown by pin-hole 

 Ijhotography, which I have been able to do with the discharge apj)ara- 



