384 SCIENTIFIC AMUSEMENTS. 



<fec., on which is painted a butterfly or other device, using different 

 phosphorescent powders for different parts of the body ; a bit of 

 magnesium wire is lighted near to the glass so as to illuminate it 

 brightly for a few seconds ; in the dark the device then shines 

 forth in brilliant colours for a short time. In most cases (but 

 not invariably) the actinic (ultra-violet) rays appear to be more 

 active in exciting phosphorescence than the visible ones, just as in 

 most instances they produce fluorescence more readily. 



