Fic. 31. Iroiuispiecc to a l^ook of Marco Antonio Cellio. // Fosfuro 

 O'l'cro la Pietra BoJogne.se (Rome, 1680) , showing the o\cn for cal- 

 cining the stone and sunbeams striking a picture drawn with the plios- 

 phor, which then luminesces in the dark. 



