Phosphorescent Light

Some experimeuts have been made in Frnnce to determine the specific aotion of a considerable lowering of temperatura upon the brilliaucy of certain bodies which shine in the dark after having been exposed tosunlight. Tubes of glass filled with tbe powdered sulphides of calcium, barium, strontium, etc, all substances possessing the property of phosphorescence in a high degree, were exposed to the solar rays and af terward provod to be lnminous in the dark, this being done in such a way as to fix upon the memory the mean valué of the progressive diminution of the emitted light, and the time also was noted during which the light was strong, less Btrong and weak respectively. The tubes were nest placed in bright sunlight for one minute and then suddenly introduced into a doublé wnüed glass cylinder, the interspaee of which was filled with nitTous oxide at 140 de_grees C. In about uve or six minutes the ture of the tubes was som e 100 degrees. They were then withdrawn, and when observerl in a perfectJy dark chamber no luminosity whatever was perceptible. As the tubes reoovored their normal teuiperature, however, the pbosphorescencrt returned vithom the exciting aReucy of the sun's raya or of diffused light. These results were proved to be general for all pbosphoresoenc substauces euiployed. The experiinents showed, too, that the production of the phosphorescent light reqnires a certain movement of the constituent moiecules of bodies.