4 CORRELATION OF PHYSICAL FORCES. 



to furnish in the notes at the conclusion such references to dif- 

 ferent 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 mo- 

 difications 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 material 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 progenitors, it is but 

 theirs added to or subtracted from, transmitted drop by drop 

 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 

 credit which they pre-eminently deserve for having devoted 

 their lives to purely intellectual pursuits, and for having 

 thought, seldom frivolously, often profoundly, nothing can be 

 more difficult than to seize and apprehend the ideas of those 

 who reasoned from abstraction to abstraction who, although, 

 as we now believe, they must have depended upon observa- 

 tion for their first inductions, afterwards raised upon them 

 such a complex superstructure of syllogistic deductions, 

 that, without following the same paths, and tracing the same 

 sinuosities which led them to their conclusions, such conclu- 

 sions are to us unintelligible. To think as another thought, 

 we must be placed in the same situation as he was placed : 

 the errors of commentators generally arise from their reason- 

 ing upon the arguments of their text, either in blind obedi- 

 ence to its dicta, without considering the circumstances under 

 which they were uttered, or in viewing the images presented 

 to the original writer from a different point to that from which 

 he viewed them. Experimental philosophy keeps in check 



