Prof. Draper on the Phosphorescence of Bodies. 97 



than to the sun. In the latter case its temperature rises, and 

 the quantity of light it fixes is less. Under violet and other 

 glasses stained with such colours as impede the warming effect, 

 phosphorescence is even more vivid than when no glass has in- 

 tervened. On the same principle, we have an explanation of 

 Dufay's apparently successful attempt to prevent the escape of 

 light from glowing diamonds, by putting them in ink or cover- 

 ing them with black wax; when removed from the ink and 

 brought out in the air, they became somewhat w^armer ; perhaps 

 the touch of the finger aided the effect, and the corresponding 

 quantity of light was set free. 



But though temperature is a controlling, it is not the only 

 condition involved. If it w^ere, phosphorescence after insolation 

 should only occur after a rise of temperature. The fundamental 

 fact of the whole inquii-y proves to us, that a glowing body can 

 retain more light in presence of a lucid surface than it can in 

 the dark. 



Is not this fact analogous to what we meet with in the ex- 

 changes of heat ? A substance can retain more heat in presence 

 of a hot body than a cold one. The brilliancy and quantity of 

 light to which a phosphorus is exposed goes veiy far to deter- 

 mine the intensity of the subsequent glow. Thus I found that 

 a piece of chlorophane exposed to one spark of a contact-breaker, 

 shone but feebly ; but if it had received one hundred sparks, its 

 light was very vivid ; and it has long been known, that in deli- 

 cate phosphori a certain degree of luminosity can be communi- 

 cated by the moonbeams, a more intense one by lamplight, and 

 one still more brilliant by the sunshine or a Leyden spark. So this 

 leads to the conclusion, that the quantity of lixjht that a body can 

 receive is directly as the intensity and quantity of light to which it 

 has been exjjosed. 



These various facts indicate, that when a ray of light falls on 

 a surface, it throws the particles thereof into a state of vibration. 

 An examination of the action of the differently coloured rays 

 dispersed by a prism, shows that, in general, the greater the fre- 

 quency of vibration of the impinging ray, the more brilliant is 

 the phos])horescence. But in such a prismatic examination, we 

 have constantly to bear in mind the disturbing agencies which 

 are present, and especially the antagonizing effects of heat ; that 

 this detennines the amount of light that a jihospliorus can re- 

 ceive;, and also the rate of its subsequent extrication. In a letter 

 whicli I ])ublished in the Fhilosophical IVIagazine, Fcbruaiy 1817, 

 it was shown how the photograpliic action of light betrays the 

 general princij)le of an interhu-ence of vil)ratory niovenu;nts, and 

 the ])roduction of antagonizing results in different parts of the 

 Holar spectrum. An argument is there brought forward to the 

 Phil. May. S. 4. Vol. 1. No. 2. Feb. 1851 . II 



