On Phosphorescence. * * 



air contained in the pores of the phosphorescent substance, 

 and the presence oF which is easily ascerianicd by puttuig 

 this substance in water under the re-ceiver ot the pneumatic 

 machine. In proportion as the air escapes, the phosphore- 

 scence diminishes, and soon disappears entirely. I he au- 

 thor ascertained that this air, aheady vitiated, only contams 

 about three-fifths of the oxygen of an equal volume ot at- 

 mospheric air. 1 • 1 » 



This kind of phosphorescence is destroyed without re- 

 medv, bv immersion m boiling water : it is suspended m 

 water at'50°, and at the freezing temperature: it subsists 



from 6" to 37=. ^ , ^ ... 



The author having put a piece of phosphorescent lish ni 

 a saline solution favourable to phosphorescence, but which 

 had been previously deprived of air by ebullition, found it 

 completelv dull after leaving it for two hours. Upon in- 

 troducing' a bubble of air into the phial, phosphorescence 

 for a few minutes was restored; new bubbles oi" air pro- 

 duced the same eft'ects; hut afterwards the phosphorescence 

 became constant as in the atmospheric air, apparently be- 

 cause the water took up that of which it had been deprived 

 by ebullition. 



ADDITION TO TIIK ABOVE MEMOIR. 



On the Power of Points upon the Fluid of Phosphorescence. 

 — M Dessaio'nes has made several additions to the above 

 experiments.'' The most remarkable has for its object the 

 new analogy which he has established, between the electri- 

 cal fluid and that of phosphorescence, by ascertaining the 

 influence of points on the phienomena presented by phos- 

 phorescent bodies. Fluor spar fractured, and presenting 

 ancles or asperities at its surface, easily takes liie on a sup- 

 porter slightly heated ; but an entire crystal of the same 

 substance, the surfaces of which have the natural poish, 

 remains dull. This is the case also wuh limpid Iceland 

 spar, Madao-ascar crvstal, limpid adular, vitreous phosphate 

 of lime, emerald, and sal gemma. A piece of glass live 

 millimetres thick remains dull even on a red-hot supporter, 

 and becomes very luminous when it has been made roui^U 

 on both sides : if it has been made rough on one side only, 

 it bhincs only when it is upon this surface that it rests on 

 the supporter. The phosphate of lime in acute-angled 

 mas.es of the first formation, presents the same plueno- 



iiicnon. • u • 



Crvstallized calcareous J>par m prisms with six pane-- 

 frminaled bv three pentagonal faces^ is formal of mchued 



lamina". 



