X PREFACE. 



"the sole factors in all electrical phenomena 

 consist in attractive and repulsive forces, inde- 

 pendent of any material substrate." Such is 

 the reverence of mankind for mysteries, that 

 the most obscure and visionary fancies are 

 often regarded as profound. It was long ago 

 remarked by Longinus, that darkness is a 

 source of the sublime : and it must be admitted 

 that objects are magnified by looming through 

 a fog. 



In all ages of the civilized world, light has 

 been recognised as a powerful agent in the 

 work of the universe. As the great painter 

 of nature, it gives to the dome of heaven its 

 azure hue, to the rainbow, its gorgeous red, 

 brilliant yellow, refreshing green, and lovely 

 blue, shading into the softer violet. It is solar 

 light which touches the morning and evening 

 clouds with its celestial pencil, when they glow 

 with vivid tints of ruby, sapphire, and gold. 

 It adorns the flowery fields with an endless 

 variety ^ of beauteous colours ; while it is per- 

 petually modifying the taste, odour, and other 

 sensible properties of whatever it touches. 



But it is still an unresolved problem, whether 

 light be a material substance, as maintained 

 by Pythagoras, Democritus, Leucippus, Em- 

 pedocles, Plato, Epicurus, Newton, and Brew- 



