OF NATURAL PHILOSOPHY. 159 



assembled cases, must lead to one of two things : 

 either, 1st, The detection of a real cause, and of its 

 manner of acting, so as to furnish a complete ex- 

 planation of the facts ; or, 2dly, The establishment 

 of an abstract law of nature, pointing out two phe- 

 nomena of a general kind as invariably connected ; 

 and asserting, that where one is, there the other 

 will always be found. Such invariable connection 

 is itself a phenomenon of a higher order than any 

 particular fact ; and when many such are discovered, 

 we may again proceed to classify, combine, and 

 examine them, with a view to the detection of their 

 causes, or the discovery of still more general laws, 

 and so on without end. 



(163.) Let us now exemplify this inductive search 

 for a cause by one general example: suppose dew 

 were the phenomenon proposed, whose cause we 

 would know. In the first place, 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 spontaneous appearance of moisture on 

 substances exposed in the open air when no rain or 

 visible wet is falling. 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 hai] chills the external air ; that 

 which runs down our walls when, after a long frost, a 

 warm moist thaw comes on : all these instances 

 agree in one point (Rule 2. 147.), the coldness of 

 the object dewed, in comparison with the air in 

 contact with it. 



