SOLAR PHOSPHOR!. 161 



We have, in answer to this, very distinct evidence that 

 some bodies do derive this property from the solar rays. 

 Canton's phosphorus, which is a sulphuret of calcium, 

 will, having been exposed to the sun, continue luminous 

 for some time after it is carried into the dark ; as will 

 also the Bolognian stone, a sulphuret of barium. This 

 result appears to be due to a particular class of the solar 

 rays ; for it has been found, if these sulphurets, spread 

 smoothly on paper, are exposed to the influence of the 

 solar spectrum for some little time, and then examined 

 in the dark, that luminous spaces appear, exactly cor- 

 responding with the most refrangible rays, or those 

 which excite chemical change ; and one very remarkable 

 fact must not be forgotten the dark rays of the spec- 

 trum beyond the violet produce a lively phosphorescence, 

 which is extinguished by the 'action of the rays of least 

 refrangibility, or the heat rays whilst artificial heat, 

 such as a warm iron, produces a very considerable 

 elevation of the phosphorescent effect.* It is not impro- 

 bable, that the fluorescent rays of Mr. Stokes may be 

 materially concerned in producing the phenomena of 

 phosphorescence : experiments are, however, required: to 

 prove this; 



In these allied phenomena we have effects which are 

 evidently dependent upon several dissimilar causes; 

 The phosphorescence of the living animalis due, with- 

 out doubt, to nervous excitation : that of the living 

 vegetable to solar luminous influence ; and in the case 

 of the mosses of caverns^ &c. to the chemical agency of 

 the sun's rays, which appears^ to be capable of con- 

 duction. In the dead organic matter we have a purely 

 chemical action developing the light, and in the inor- 



* Des Effets produits sur les corps par les Rayons Solaires: 

 par M. Edmond Becquerel. Annales de. Chimie, vol. ix. p. 267. 

 1843. 



M. Becquerel has applied the term phosphorogcnique to those. 

 rays producing phosphorescence. 



M 



