PRELUDE. 61 



ately lead man to profound physical knowledge, answered some nobler 

 and better purpose in his constitution and government. The fact un- 

 doubtedly was, that the physical philosophy of the Greeks soon became 

 trifling and worthless ; and it is proper to point out, as precisely as we 

 can, in what the fundamental mistake consisted. 



To explain this, we may in the first place return for a moment to 

 Ilerodotus's account of the cause of the floods of the Nile. 



The reader will probably have observed a remarkable phrase used 

 by Herodotus, in his own explanation of these inundations. He says 

 that the sun draws, or attracts, the water ; a metaphorical term, ob- 

 viously intended to denote some more general and abstract conception 

 than that of the visible operation which the word primarily signifies. 

 This abstract notion of " drawing" is, in the historian, as we see, very 

 vague and loose ; it might, with equal propriety, be explained to mean 

 what we now understand by mechanical or by chemical attraction, or 

 pressure, or evaporation. And in like manner, all the first attempts 

 to comprehend the operations of nature, led to the introduction of 

 abstract conceptions, often vague, indeed, but not, therefore, un- 

 meaning ; such as motion and velocity, force and pressure, impetus 

 and momentum (po^). And the next step in philosophizing, neces- 

 sarily was to endeavor to make these vague abstractions more clear 

 and fixed, so that the logical faculty should be able to employ them 

 securely and coherently. But there were two ways of making this 

 attempt ; the one, by examining the words only, and the thoughts 

 which they call up ; the other, by attending to the facts and things 

 which bring these abstract terms into use. The latter, the method of 

 real inquiry, was the way to success; but the Greeks followed the 

 former, the verbal or notional course, and failed. 



If Herodotus, when the notion of the sun's attracting the waters 

 of rivers had entered into his mind, had gone on to instruct himself, 

 by attention to facts, in what manner this notion could be made more 

 definite, while it still remained applicable to all the knowledge which 

 could be obtained, he would have made some progress towards a true 

 solution of his problem. If, for instance, he had tried to ascertain 

 whether this Attraction which the sun exerted upon the waters of 

 rivers, depended on his influence 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 observations sufficiently obvious, that the sun's Attrac- 

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



