EXAMPLES OF THE FOUR METHODS. 491 



themselves of the purport of the speculation as a 

 whole, before applying themselves, with me, to the 

 logical analysis of the different steps of. the argu- 

 ment. 



" Suppose dew were the phenomenon proposed, 

 whose cause we would know. In the first place" we 

 must determine precisely what we mean by dew ; 

 what the fact really is, whose cause we desire to 

 investigate. " We must separate dew from rain, and 

 the moisture of fogs, and limit the application of the 

 term to what is really meant, which is, the sponta- 

 neous appearance of moisture on substances exposed 

 in the open air when no rain or visible wet is 

 falling." This answers to a preliminary operation 

 which will be characterised in the ensuing book, 

 treating of operations subsidiary to induction*. The 

 state of the question being fixed, we come to the 

 solution. 



" Now, here we have analogous phenomena in the 

 moisture which bedews a cold metal or stone when we 

 breathe upon it ; that which appears on a glass of 

 water fresh from the well in hot weather ; that which 

 appears on the inside of windows when sudden rain or 

 hail chills the external air ; that which runs down our 

 walls when, after a long frost, a warm moist thaw 

 comes on." Comparing these cases, we find that they 

 all contain the phenomenon which was proposed as 

 the subject of investigation. Now " all these instances 

 agree in one point, the coldness of the object dewed, 

 in comparison with the air in contact with it." But 

 there still remains the most important case of all, 

 that of nocturnal dew : does the same circumstance 



Vide infra, book iv., chap. ii. On Abstraction. 



