10 On Phosphorescence. 



deprive them of this property, except by rendering them 

 less susceptible of permitting the passage of the electric 

 fluid, and not because a small quantity of water is indis- 

 peiibable for the production of this plia^noinenon. 



The fourth chapter of M. Dcssaigucs' Memoir treats of 

 phosphorescence by collision. All bodies suscepiible of 

 shining in this manner are also, with very few exi^eptions, 

 luminous on the heated supporter, by exposure to light and 

 by electrization. This property also diminishes in propor- 

 tion as bodies are more or less conipletclv calcined : never- 

 theless glass, calcined until it has become inphosphorescent 

 by every oiher method, also en)its a brisk light under the 

 action of the file ; but in order to produce this etiect the 

 friction must be much stronger than before calcination. 

 This kind of phosphorescence, which takes place like the 

 foregoing in vacuo, and in the irrespirable gases, seems be- 

 sides, from the wliole phasnomena, to be produced by the 

 same cause. The author attributes it to the oscillations of 

 a particular fluid whicJi heat, light, electricitv, and a blow 

 or friction put in motion j and that calcination, or a long 

 exposure to the light, drives it from bodies which are ex- 

 posed to it : but we do not find, on this hypothesis, how 

 strong electrical discharges reproduce the phosphorescence, 

 unless this fluid and the electrical fluid are one and the 

 same. The author thinks this opinion oue,ht to be rejected, 

 because we perceive no si^n of electrical attraction, or re- 

 pulsion, in bodies which have recovered in this way the 

 phosphorescence which they had lost, and Ijecause it is ex- 

 cited by an electrical discharge in various bodies plunged 

 under water. But if we recollect that water is a ver\' b;!d 

 conductor of the electrical iluidjand tliat we are but imper- 

 fectly acquainied with ih.e various iiiodiiications of which 

 this fluid is susceptible, anJ the cause of tlie briiiianl light 

 which it gives in vacuo, we may naturally look for new 

 facts, before we decide tint the fluid of p!iosj)horesceiice is 

 essentially dillcrenl from ihal to which we ascribe tlie pha;- 

 nomcna of elect ncily. 



M. Dcssaigucs examines, in the fifth chapter of liis me- 

 moir, the sponlau'.ous phosphorescence of animal and ve- 

 getable substances. He concludes from his experiments, 

 that it is owing to a true combustimi, in which water and 

 carbonic acid are formed: we easily ascertain the presence of 

 this acitl in the lesiduum by means of lime-wfe'er. Wood 

 loses more than halt its weiiilu before ceasing to shine. 

 This phorphoresctnc;; is not extinguished until after some 

 time in the irrctpira'o'c gises, but this is on account of the 



air 



