56 Trowbridge and Burbank — Phosphoresence, etc. 



electrical discharges does not cause phosphorescence ; but the 

 phosphorescence is due to peculiar discharge rays analogous to 

 cathode rays.* M. W. Hoffmann has confirmed Wiedemann's 

 work.f The latter states that no " Entladungsstrahlen" could 

 be detected in the brush discharge. 



"With the preparation of fluorite, we have mentioned above, 

 no effect was produced by the light of the electrical discharge. 

 It was submitted, according to the method of Becquerel, to the 

 light of the spark; and it was also exposed to the light of burn- 

 ing magnesium, and to that of the voltaic arc ; and no direct 

 phosphorescent effects could be produced, nor by subsequent 

 heating. It phosphoresced, however, on heating after having 

 been electrified by the brush discharge. The phosphorescence 

 was evidently an expression of the electrical energy, which 

 was communicated to the substance, and this energy was sud- 

 denly converted into light by the action of the heat in dispel- 

 ling the electricity. The substance was next subjected to the 

 action of the X-rays, in a brass box, closed by an aluminum 

 window. The box was also connected to the ground. When 

 the substance was taken from the metallic box it showed no 

 phosphorescence, but on being heated it exhibited a bright 

 phosphorescence which quickly disappeared. 



The action of the X rays on this mineral was exactly similar 

 to that of electrification ; and we cannot but regard our experi- 

 ments as an evidence of the electrical nature of the action of 

 the X-rays. By them an electrical charge is communicated to 

 a fluorescent and phosphorescent substances. The resulting 

 electrical energy, in being dissipated, produces the phenomenon 

 of light. By heating crystals which have been electrified, we 

 produce a sudden dissipation of the electrical energy which 

 has been communicated to the particles of the phosphorescent 

 substance — either by direct electrification or by the electrifica- 

 tion produced by the X-rays. 



Most phosphorescent substances, after having been submitted 

 to sunlight or daylight, glow more strongly when heated. 

 The phosphorescence, however, dies out quicker after the pro- 

 cess of heating, which seems to cause the energy communicated 

 to the substance by light to become dissipated more quickly. 

 The same thing is true of the state of phosphorescence com- 

 municated by the X rays. Can we, therefore, conclude that 

 the phosphorescence excited by sunlight or daylight is due to an 

 electrical condition which can be dissipated by heat? This sup- 

 position seems to us not inconsistent with the electromagnetic 

 theory of light, and phosphorescence may be an' evidence of 

 the electrical stresses which produce the phenomena of ultra- 

 violet light. 



Jefferson Physical Laboratory, Harvard University. 



* Wied. Ann., lvi, 1895, p. 237. f Wied. Ann., No. 2, 1897, p. 273. 



