198 PRACTICAL CONSIDERATIONS. 



plied to so many useful purposes by engineers, 

 astronomers, microscopical observers, etc. 



The same arguments might apply to the Elec- 

 tric Light; but it has not yet been proved that 

 this is identical with phosphorescence, though 

 such is the opinion of some philosophers, as we 

 have already seen. 



Again, I have alluded, in the first part of this 

 work, to the fact that houses freshly painted with 

 lime-wash are frequently luminous at night, though 

 slightly, after exposure to the sun's rays during 

 the day. If, by chemical and physical research, a 

 means were discovered capable of rendering this 

 phosphoric light more powerful, by employing sul- 

 phides of calcium or barium, etc., and superadd- 

 ing, if necessary, the action of an electric cur- 

 rent when the sun is hidden by clouds, a street 

 might be effectively illuminated by phosphorescent 

 light alone. 



The light of the Elaterida, or Fireflies, has for 

 years been employed for lighting apartments, and 

 in travelling, in the West Indies. 



Phosphorus dissolved in oil has been sometimes 

 used as a night-light. As long as the bottle which 

 contains the liquid remains closed no light is seen ; 

 but when opened the phosphorescence is suffi- 

 ciently bright to enable us to read the hour upon 

 a watch, etc. These luminous bottles were once 

 much in vogue as useful curiosities. 



