158 THE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



then, that we could detect that of a source three thou- 

 sand times less intense ? 



I conclude, therefore, that all phosphoric bodies emit 

 radiant heat as well as light ; but that its quantity is so 

 small that we have no means delicate enough to measure 

 it, though the eye is so sensitive that it can detect the 

 light, the absolute intensity of which has, however, hith- 

 erto been greatly overrated. I believe that the quanti- 

 ties of both are of the same order, and if this be true we 

 should scarcely expect to discover any dilatation of the 

 glowing body unless means much more refined than 

 those here resorted to are employed. 



