OF NATURAL PHILOSOPHY. 77 



thus distinguishing observation from experiment, 

 to place them in any kind of contrast. Essentially 

 they are much alike, and differ rather in degree 

 than in kind ; so that, perhaps, the terms passive 

 and active observation might better express their 

 distinction ; but it is, nevertheless, highly im- 

 portant to mark the different states of mind in 

 inquiries carried on by their respective aids, as 

 well as their different effects in promoting the 

 progress of science. In the former, we sit still 

 and listen to a tale, told us, perhaps obscurely, 

 piecemeal, and at long intervals of time, with 

 our attention more or less awake. It is only by 

 after-rumination that we gather its full import ; 

 and often, when the opportunity is gone by, we 

 have to regret that our attention was not more 

 particularly directed to some point which, at the 

 time, appeared of little moment, but of which we 

 at length appretiate the importance. In the latter, 

 on the other hand, we cross-examine our witness, 

 and by comparing one part of his evidence with 

 the other, while he is yet before us, and reasoning 

 upon it in his presence, are enabled to put pointed 

 and searching questions, the answer to which may 

 at once enable us to make up our minds. Accord- 

 ingly it has been found invariably, that in those 

 departments of physics where the phenomena are 

 beyond our control, or into which experimental 

 enquiry, from other causes, has not been carried, 

 the progress of knowledge has been slow, uncertain, 

 and irregular ; while in such as admit of expe- 

 riment, and in which mankind have agreed to its 

 adoption, it has been rapid, sure, and steady. For 



