334 



SCIENTIFIC RECREATIONS. 



thus prepared to the light of the sun, or the rays emanating from magnesium 

 wire in a state of combustion (fig. 319), to produce immediate phospho- 

 rescent effects. If taken into a dark room (fig. 320) they shine with great 

 brilliancy, and give off very exquisite coloured rays. Phosphorescent sulphates 

 are used also in tracing names or designs on a paper surface, etc., and it 

 can easily be conceived that such experiments may be infinitely varied 

 according to the pleasure of the experimenter. 



But let us ask ourselves if these substances are not capable of being 



Fig. 320. Phosphorescent flower emitting light in a dark room. 



put to more serious uses, and of being classed among useful products. To 

 this we can reply very decidedly in the affirmative. With phosphorescent 

 matter we can obtain luminous faces for clocks placed in dark, obscure 

 spots, and it is not impossible to use it for making sign-boards for shops, or 

 numbers of houses, which can be lit up at night. Professor Norton even 

 goes so far as to propose in the " Journal of the Franklin Institute," not 

 only coating the walls of rooms with these phosphorescent substances, but 

 also the fronts of houses, when he considers it would be possible to do away 

 entirely with street lights, the house-fronts absorbing sufficient light during 

 the day to remain luminous the whole of the night. 



