LECTURE X. 



EXPERIMENTAL PHILOSOPHY. 



LIGHT. 



IN considering the nature of light, a difficulty 

 presents itself similar to that which occurred with 

 respect to the electrical fluid. Some philosophers 

 have been disposed to consider the matter of light 

 as essentially different from elementary fire, while 

 others have regarded them as intrinsically the 

 same matter, only exhibited in different states. 

 A late writer on these subjects conjectures that 

 light is diluted fire, that is, fire weakened and 

 diffused as spirits when mingled with water ; and 

 another terms it fire in a projectile state, that is, 

 its particles are separately projected, and, in 

 truth, at an immense distance from each other, 

 whereas in culinary fire it is collected and con- 

 densed. It is a circumstance which not a little 

 favours this latter opinion, that light may be col- 

 lected and condensed by what is called a burning- 

 glass, so as to burn like the fiercest flame. On the 

 contrary, flame itself may be so diluted or diffused 

 as to be perfectly innoxious. " The flame,*" says 

 Dr. Goldsmith, ei which hangs over burning 

 spirit of wine, we all know to scorch with great 

 power; yet these flames may be made to shine 

 as bright as ever,yet be perfectly harmless. This 



