MEMOIR VIII.] THE PHOSPHORESCENCE OF BODIES. J53 



GENERAL CONCLUSIONS. 



The results to which the foregoing experiments bring 

 us are therefore 



1st. That the methods employed in these experiments 

 are not sufficiently delicate to detect any increase in the 

 dimensions of a phosphorus while it is in a glowing state. 



2d. No structural change can be discovered by resort- 

 ing to polarized light ; but there is reason to believe 

 from the change of color which certain bodies exhibit 



^j 



when the quality of shining is communicated to them, 

 and from the manner in which 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 elec- 

 trical 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 dis- 

 covered 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 that 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. 



Determination of the absolute quantity of light emitted 

 by phosphori. 



And now we may inquire how it is with the light it- 

 self? do we not deceive ourselves respecting it? We 

 ought to recollect that it is barely perceptible in the 

 open day, and that these experiments require to be made 



