76 PHOSPHORESCENCE. 



the key will be visible. Let this paper be put 

 aside for many months where nothing can disturb 

 it, and then in darkness be laid on a plate of hot 

 metal, the spectre of the key will again appear. 



In the cases of bodies more highly phospho- 

 rescent than paper, the spectres of many different 

 objects which may have been laid on in succession 

 will, on warming, emerge in their proper order. 



