164 DISCOURSE ON THE STUDY 



terminate when traced to its insertion in the trunk, 

 or a twig to its junction with the branch ; or rather, 

 as a rivulet retains its importance and its name till 

 lost in some larger tributary, or in the main river 

 which delivers it into the ocean. This, however, al- 

 ways supposes that, on a reconsideration of the case, 

 we see clearly how the admission of such a fact, 

 with all its attendant laws, will perfectly account 

 for every particular as well those which, in the dif- 

 ferent stages of the induction, have led us to a know- 

 ledge of it, as those which we had neglected, or 

 considered less minutely than the rest. But, had 

 we no previous knowledge of the radiation of heat, 

 this same induction would have made it known to 

 us, and, duly considered, might have led to the 

 knowledge of many of its laws. 



(170.) In the study of nature, we must not, 

 therefore, be scrupulous as to how we reach to a 

 knowledge of such general facts : provided only 

 we verify them carefully when once detected, we 

 must be content to seize them wherever they are to 

 be found. And this brings us to consider the veri- 

 fication of inductions. 



(171.) If, in our induction, every individual case 

 has actually been present to our minds, we are sure 

 that it will find itself duly represented in our final con- 

 clusion : but this is impossible for such cases as 

 were unknown to us, and hardly ever happens even 

 with all the known cases ; for such is the tendency 

 of the human mind to speculation, that on the least 

 idea of an analogy between a few phenomena, it 

 leaps forward, as it were, to a cause or law, to the 

 temporary neglect of all the rest ; so that, in fact, 



