SIMPLE PHOSPHOROSCOPE. 403 



parent and opaque objects, the latter more particularly to trans- 

 parent objects which, being at rest, are more distinctly seen ; an 

 advantage in the case of cut gems. 



In one or the other of these ways I have obtained beautiful 

 results from uranium glass, cut rubies, semi-transparent corun- 

 dum and willemite. I have not yet had an opportunity to try 

 a diamond affording an afterglow. 



It is evident that both opaque and transparent substances may 

 be examined by this instrument, either fixed upon the outside 

 of the cylinder, or held within it, as described ; and in either 

 case its indications are quite sensitive, inasmuch as it may be 

 given so high a speed that only a very small fraction of a second 

 elapses after the object is illuminated and before its presentation 

 in absolute darkness to the eye of the observer. Moreover, in 

 either case, one object may be substituted for another quickly 

 and easily, and the brilliancy obtained from some minerals, es- 

 pecially rubies, is quite surprising. 



