MAGNESIUM AND ELECTRIC LIGHTS. 161 



each other at all temperatures, there is a vast difference in 

 this respect between solids and gases. Gases, however 

 highly they are heated, for some mysterious reason or 

 other, emit comparatively very little light. There is a curi- 

 ous experiment to show this. If a thin plate of platinum 

 is held over the flame of a lamp at a place where the as- 

 cending gases are not at all luminous, it becomes incandes- 

 cent itself at once that is, a degree of heat which makes 

 the solid emit a bright light, will not cause the gas to emit 

 any at all." 



" Would it be the same with a thin piece of iron or 

 steel," asked John " a piece of watch-spring, for exam- 

 ple?" 



" I don't know," replied Lawrence. " Perhaps it might 

 over an Argand lamp, or any lamp on that principle, with 

 a glass chimney." 



"I mean to try it some day," said John. 



"I would do so," said Lawrence. "And now for the 

 fourth light, which is 



" 4. THE MAGNESIUM LIGHT." 



But what Lawrence said on this head need not be re- 

 peated, as the manner in which a very bright light is pro- 

 duced by the combustion of magnesium, and by the intense 

 incandescence of the solid particles of magnesia which re- 

 sult, has already been fully explained. 



"And now," continued Lawrence, after having finished 

 what he had to say under the fourth head, "we come to 



" 5. THE ELECTRIC LIGHT. 



" This light is on the same principle with the others in 

 respect to its being produced through the incandescence 

 of solid particles by intense heat, and the particles, too, are 

 particles of carbon ; but the heat is produced in another 

 way, and that is not by any process of combustion, but by 

 electricity. 



