OF NATURAL PHILOSOPHY. 299 



(334.) It is the business of chemistry to investigate 

 these and similar changes, or the reverse of such 

 changes, where a single substance is resolved into 

 two or more others, having different properties from 

 it, and from each other, and to enquire into all the 

 circumstances which can influence them ; and either 

 determine, modify, or suspend their accomplish- 

 ment, whether such influence be exercised by heat 

 or cold, by time and rest, or by agitation or pres- 

 sure, or by any of those agents of which we have 

 acquired a knowledge, such as electricity, light, 

 magnetism, &c. 



(335.) The wonderful and sudden transformations 

 with which chemistry is conversant, the violent ac- 

 tivity often assumed by substances usually considered 

 the most inert and sluggish, and, above all, the insight 

 it gives into the nature of innumerable operations 

 which we see daily carried on around us, have con- 

 tributed to render it the most popular, as it is one of 

 the most extensively useful, of the sciences ; and we 

 shall, accordingly, find none which have sprung 

 forward, during the last century, with such extra- 

 ordinary vigour, and have had such extensive in- 

 fluence in promoting corresponding progress in 

 others. One of the chief causes of its popularity is, 

 perhaps, to be sought for in this, that it is, of all the 

 sciences, perhaps, the most completely an expe- 

 rimental one ; and even its theories are, for the 

 most part, of that generally intelligible and readily 

 applicable kind, which demand no intense concen- 

 tration of thought, and lead to no profound mathe- 

 matical researches. The simple process of inductive 

 generalization, grounded on the examination of nu- 



