PRELUDE. 37 



at their fountains only, or was exerted over their 

 whole course, and over waters which were not parts 

 of rivers, he would have been led to reject his 

 hypothesis; for he would have found, by observa- 

 tions sufficiently obvious, that the sun's Attraction, 

 as shown in such cases, is a tendency to lessen all 

 expanded and open collections of moisture, whether 

 flowing from a spring or not ; and it would then be 

 seen that this influence, operating on the whole 

 surface of the Nile, must diminish it as well as 

 other rivers, in summer, and therefore could not 

 be the cause of its overflow. He would thus have 

 corrected his first loose conjecture by a real study 

 of nature, and might, in the course of his medita- 

 tions, have been led to available notions of Evapora- 

 tion, or other natural actions. And, in like manner, 

 in other cases, the rude attempts at explanation, 

 which the first exercise of the speculative faculty 

 produced, might have been gradually concentrated 

 and refined, so as to fall in, both with the requisi- 

 tions of reason and the testimony of sense. 



But this was not the direction which the Greek 

 speculators took. On the contrary ; as soon as they 

 had introduced into their philosophy any abstract 

 and general conceptions, they proceeded to scrutinize 

 these by the internal light of the mind alone, with- 

 out any longer looking abroad into the world of 

 sense. They took for granted that philosophy must 

 result from the relations of those notions which are 

 involved in the common use of language, and they 



