196 DISCOURSE ON THE STUDY 



ous bodies, and acted upon in their progress by 

 forces of extreme intensity residing in the sub- 

 stances on which they strike ; another, in the vi- 

 bratory motion of the particles of luminous bodies, 

 communicated to a peculiar subtle and highly elas- 

 tic ethereal medium, filling all space, and conveyed 

 through it into our eyes, as sounds are to our ears, 

 by the undulations of the air. 



(208.) Now, are we to be- deterred from fram- 

 ing hypotheses and constructing theories, because 

 we meet with such dilemmas, and find ourselves 

 frequently beyond our depth? Undoubtedly not. 

 Est quodam prodire tenus si non datur ultra. 

 Hypotheses, with respect to theories, are what 

 presumed proximate causes are with respect to 

 particular inductions : they afford us motives for 

 searching into analogies ; grounds of citation to 

 bring before us all the cases which seem to bear 

 upon them, for examination. A well imagined 

 hypothesis, if it have been suggested by a fair 

 inductive consideration of general laws, can hardly 

 fail at least of enabling us to generalize a step 

 farther, and group together several such laws under 

 a more universal expression. But this is taking a 

 very limited view of the value and importance of 

 hypotheses : it may happen (and it has happened 

 in the case of the undulatory doctrine of light) 

 that such a weight of analogy and probability may 

 become accumulated on the side of an hypothesis, 

 that we are compelled to admit one of two things ; 

 either that it is an actual statement of what really 

 passes in nature, or that the reality, whatever it be, 

 must run so close a parallel with it, as to admit of 



