194 ANNUAL OF SCIENTIFIC DISCOVERY. 



Stokes showed the effect of cobalt, uranium, solution of chlorophylle, 

 sulphate of quinia, and other substances, and gave this verbal state- 

 ment of the application of optical researches to abridge chemical labor. 



PHOSPHORESCENCE OF BODIES. 



PROF. DRAPER, of New York, has communicated to the Philo- 

 sophical Magazine, a paper of experimental researches, " On the 

 Phosphoresence of Bodies," whence we obtain the following general 

 conclusions : 



1st. That the methods employed in these experiments are not suf- 

 ficiently delicate to detect any increase of the dimensions of a phos- 

 phorescent while it is in a glowing state. 



2d. No structural change can be discovered by resorting to polar- 

 ized light ; but there is reason to believe", from the change of color 

 which certain bodies exhibit when the quality of shining is communi- 

 cated to them, and from the manner that vapors condense on their 

 surfaces, that such has actually taken place. 



3d. That phosphorescence is attended with a minute rise of 

 temperature. 



4th. That it is not necessarily connected with any electrical 

 disturbance. 



On comparing these conclusions, it is obvious, that if the third be 

 correct, there must necessarily be a change of volume ; and that the 

 reason the dilatation is not discovered by direct experiment, is owing 

 to the insufficiency of the means employed. 



The general definition given of phosphorescence is, that it is the 

 extrication of light without heat, (Gmelin.) But these results show 

 that such definition is essentially incorrect ; for, if the experiment be 

 made with due care, a rise of temperature can be detected, though its 

 absolute amount may be very small. 



With respect to the absolute quantity of light emitted by phosphori, 

 Prof. Draper, from an experiment several times repeated, concludes 

 that the intrinsic brilliancy of phosphori is very small ; a fine specimen 

 of chlorophane, at its maximum of brightness, yielding a light 

 three thousand times less intense than the flame of a very small oil 

 lamp. 



From certain experiments and considerations it is to be inferred, 

 that there is an intimate connection between temperature and phos- 

 phorescence, which may be conveniently expressed in the following 

 terms : 



The quantity of light a substance can retain is inversely as its 

 temperature. 



Again, this principle leads to the conclusion, that the quantity ol 

 light that a body can receive is directly as the intensity and quantity 

 of light to which it has been exposed. 



In conclusion, Prof. Draper is led to believe, that all the facts of 

 phosphorescence can be fully explained on the principles of the com- 



