PEEFACE. 



A SKETCH of the thoughts expressed in the following 

 pages was given in two lectures to the Members of 

 the Edinburgh Philosophical Institution in November 

 1866. Exciting considerable interest at the time, 

 and receiving through the newspapers a wider 

 audience than that to which they were originally 

 addressed, these lectures, as might have been ex- 

 pected, met with a somewhat varied reception. By 

 many the views they contained were adopted without 

 reserve ; by some, though not adopted, they were 

 received in a spirit of candour and inquiry ; while by 

 a few the whole argument was met with the most 

 vehement and unreasoning opposition. Had the last 

 contented themselves with merely opposing — every 

 man having a right to the free utterance of his 

 opinions — the argument on the author's part might 

 have terminated with the lectures ; but as they re- 



