670 POPULAR SCIEiYCE MONTHLY. 



photogTaphically than the X rays, but it could not penetrate solid 

 materials. This ]U'operty was given to it by its passage through 

 rarefied space. I then covered a screen with a phosphorescent sub- 

 stance, and exposed it to the spark in air. The phosphorescent 

 light could barely be detected at a distance of three feet, while 

 with a spark in rarefied air it could be seen at a distance of twenty 

 feet. 



"When we consider these experiments we see that the X rays 

 act toward phosphorescent matter much as the spark in air behaves 

 toward the photographic plate. Now, these results, taken in con- 

 nection with the strong electrical effects in the neighborhood of an 

 excited Crooke's tube, points to a certain connection between phos- 

 phorescence and electricity. Can it be that the strange light is 

 excited by very short electrical waves sent out from the tube, which 

 can not travel far but are very active in producing molecular 

 effects? This activity, indeed, may prevent their extending to great 

 distances. "Wireless telegraphy evidently depends upon one set of 

 waves sent out by a spark, and X-ray photographs upon another 

 set developed only in rarefied air. Phosphorescence can not be 

 produced with ease by the spark in air. On the contrary, it is 

 developed to a remarkable degree and at comparatively great dis- 

 tances by the discharge in rarefied air. It has been shown by Mr. 

 Burbank and myself that electrical force can develop phosphores- 

 cent light in certain crystals. The sunlight can do the same. Is 

 sunlight an electrical phenomenon? That it is constitutes the 

 greatest hypothesis in physics of this century. W^hen we reflect, 

 too, that the phosphorescence of the firefly is excited by some mani- 

 festation of a living organism — nerve force or some related force 

 — shall we not include nerve force in the electrical category? 



The X rays, therefore, bring into prominence strange lights 

 which had heretofore been noticed chiefly by keen-eyed investi- 

 gators, and which, with their names, phosphorescence and fluores- 

 cence, were unknown to the bulk of mankind. The fluorescent 

 screen, by means of which siirgeons observe the skeleton of the 

 body, has now taken its place in medical practice with the stetho- 

 scope, by which the mechanism of the lungs is studied, and hopes 

 have been excited that the blind may yet use the X rays in detect- 

 ing objects and in regaining a sense of vision, even though this 

 sense may be only partial. It is a curious fact that the retina of 

 the eye is phosphorescent and fluorescent, and that one can see 

 the shadow of certain objects in the dark when one stands so that 

 the feeble X rays fall upon the eye. In other words, the retina 

 acts as a fluorescent screen. The eye at present recognizes only 

 a limited number of the waves that are surging about us. We can 



