PHENOMENA OF DI POLARIZED LIGHT. 425 



attempts on the part of philosophers to combine 

 them all under the dominion of some wide and pro- 

 found theory. Endeavours to ascend from such 

 knowledge as we have spoken of, to the general 

 theory of light, were, in fact, made at every stage 

 of the subject, and with a success which at last won 

 almost all suffrages. We are now arrived at the 

 point at which we are called upon to trace the his- 

 tory of this theory; to pass from the laws of pheno- 

 mena to their causes; from Formal to Physical 

 Optics. The undulatory theory of light, the only 

 discovery which can stand by the side of the theory 

 of universal gravitation, as a doctrine belonging to 

 the same order, for its generality, its fertility, and 

 its certainty, may properly be treated of with that 

 ceremony which we have hitherto bestowed only on 

 the great advances of astronomy; and I shall there- 

 fore now proceed to speak of the Prelude to this 

 epoch, the Epoch itself^ and its Sequel, according to 

 the form of the preceding book. 



