12 CORRELATION OF PHYSICAL FORCES. 



more or less on the subject, have subsequently been pointed 

 out to me, some of which go back to a distant period. An 

 attempt to analyse these in detail, and tp trace how far I 

 have been anticipated by others, would probably but little 

 interest the reader, and in the course of it I should constantly 

 have to make distinctions showing wherein I differed, and 

 wherein I agreed with others. I might cite authorities which 

 appear to me to oppose, and others which appear to coincide 

 with certain of the views I have put forth ; but this would 

 interrupt the consecutive developement of my own ideas, and 

 might render me liable to. the charge of misconstruing those of 

 others ; I therefore think it better to avoid such discussion in 

 the text ; and in addition to the sketch given in the Preface, 

 to furnish in the notes at the conclusion such references 

 to different authors as bear upon the subjects treated of, 

 which I have discovered, or which have been pointed out to 

 me since the delivery of the lectures of which this essay 

 is a record. 



The more extended our research becomes, the more we 

 find that knowledge is a thing of slow progression, that the 

 very notions which appear to ourselves new, have arisen, 

 though perhaps in a very indirect manner, from successive 

 modifications of traditional opinions. Each word we utter, 

 each thought we think, has in it the vestiges, is in itself the 

 impress, of antecedent words and thoughts. As each ma- 

 terial form, could we rightly read it, is a book, containing in 

 itself the past history of the world ; so, different though our 

 philosophy may now appear to be from that of our progeni- 

 tors, it is but theirs added to or subtracted from, transmitted 

 drop by arop through the filter of antecedent, as ours will be 

 through that of subsequent, ages. The relic is to the past as 

 is the germ to the future. 



Though many valuable facts, and correct deductions from 

 them, are to be found scattered amongst the voluminous 

 works of the ancient philosophers ; yet, giving them the 



