LATEST DEVELOPMENTS WITH THE X RAYS. 669 



When the Crooke's tube is excited we are conscious of a mysterious 

 activity within it, for its glass walls glow with a phosphorescent 

 light, and if certain crystals, like the diamond or the ruby, are 

 placed in the tube, this phosphorescent light is vivid. Outside the 

 tube, in free air, these luminescent effects are also present. The 

 air is under an electrical strain, which is shown by the auroral 

 streamers when this air is rarefied, and an electrical charge can not 

 be maintained on a pith ball — it is dissipated in some strange man- 

 ner. Still stranger, an electrical current is greatly aided by the 

 X rays in its endeavor to pass through air — they make for the time 

 being air a conductor. Furthermore, these rays separate the air 

 into positively laden and negatively laden particles. 



The electrical discharge in the Crooke's tube is many-sided in 

 its manifestations. Its energy seems all-pervading in the room 

 where it occurs. Before the discharge passes through the rare- 

 fied space in the tube its energy manifests itself by a crackling 

 spark, a miniature lightning discharge. This spark, five or six 

 inches in length, can send out inagnetic waves which extend far 

 beyond the narrow limits of the room. They can be detected, by 

 the methods of wireless telegraphy, fifty miles. "Wlien the same 

 amount of energy is developed in a Crooke's tube the magnetic 

 waves hardly pass beyond the walls of the room, and the phenome- 

 non of phosphorescence and fluorescence and the strange molec- 

 ular eifccts outside the Crooke's tube spring into prominence. 

 The crackling spark outside the tube is far-reaching in its effect, 

 yet it shows no signs of the X rays, its light can not penetrate the 

 human body, it excites only a feeble phosphorescence at a distance 

 of even two or three feet, while the same energy excited in the 

 Crooke's tube can cause luminescence at a distance of twenty feet. 

 The crackling spark, however, can be seen much farther than the 

 light of the Crooke's tube, and it can also impress a photographic 

 plate at much greater distance. The following experiments will 

 illustrate the different manifestations of energy of which an elec- 

 trical discharge is capable. I produced an electrical spark about 

 six inches in length and exposed a photographic plate for six sec- 

 onds, at a distance of two, ten, and twenty feet, to its light, A 

 thin strip of tin, with a circular hole cut in it, served as a shutter. 

 The sensitive plate was thus protected, except in front of this aper- 

 ture. The images exhibit the decrease in light with the increase 

 of distance. Another portion of the sensitive plate was exposed 

 in the same manner during the same length of time to the light 

 of a Crooke's tube which was excited by this same spark. No 

 image was obtained at a distance 'of ten feet, and barely one at 

 three feet. The spark in "air, therefore, was far more energetic 



