276 



EXPLANATIONS. 



on an equal footing in respect to evidence with the ax- 

 ioms of geometry itself. 



" I apprehend that the considerations which give, at. the 

 present day, to the proof of the law of uniformity of suc- 

 cession as true of all phenomena without exception, this 

 character of completeness and conclusiveness, are the fol- 

 lowing : First, that we now know it directly to be true of 

 by far the greatest number of phenomena ; that there are 

 none of which we know it not to be true, the utmost that 

 can be said being, that of some we cannot positively, from 

 direct evidence, affirm its truth ; while phenomenon after 

 phenomenon, as they become better known to us, are con- 

 stantly passing from the latter class into the former ; and in 

 all cases in which that transition has not yet taken place, 

 the absence of direct proof is accounted for by the rarity 

 or the obscurity of the phenomena, our deficient means of 

 observing them, or the logical difficulties arising from the 

 complication of the circumstances in which they occur ; 

 insomuch that, notwithstanding as rigid a dependence 

 upon given conditions as exists in the case of any other 

 phenomenon it was not likely that we should be better ac- 

 quainted with those conditions than we are. Besides this 

 first class of considerations, there is a second, which still 

 further corroborates the conclusion, and from the recog- 

 nition of which the complete establishment of the univer- 

 sal law may reasonably be dated. Although there are 

 phenomena, the production and changes of which elude 

 all our attempts to reduce them universally to any ascer- 

 tained law yet in every such case the phenomenon, or the ob- 

 jects concerned in it, are found in some instances to obey 

 the known laws of nature. The wind, for example, is the 

 type of uncertainty and caprice, yet we find it in some 

 cases obeying with as much constancy as any phenomena 

 in nature the law of the tendency of fluids to distribute 

 themselves so as to equalize the pressure on every side oi 

 each of their particles ; as in the case of the trade winds 

 and the monsoons. Lightning might once have been sup- 

 posed to obey no laws ; but since it has been ascertained to 

 be identical with electricity, we know that the very same 

 phenomenon, in some of its manifestations, is implicitly 

 obedient to the action of fixed causes. / do not believe 

 that there is now one object or event in all our experience 

 of nature, within the bounds of the solar system at least, 

 which has not either been ascertained by direct observation 



