258 HISTORY OF GALVANISM. 



tionary ; the steps of scientific induction are our definitions. It is 

 only by going back through the successful researches of men respect- 

 ing the composition and elements of bodies, that we can learn in what 

 sense such terms must be understood, so as to convey real knowledge. 

 In order that they may have a meaning for us, we must inquire what 

 meaning they h^d in the minds of the authors of our discoveries. 



And thus we cannot advance a step, till we have brought up our 

 history of Chemistry to the level of our history of Electricity ; till 

 we have studied the progress of the analytical, as well as the mecha- 

 nical sciences. We are compelled to pause and look backwards here ; 

 just as happened in the history of astronomy, when we arrived at the 

 brink of the great mechanical inductions of Newton, and found that 

 we must trace the history of Mechanics, before we could proceed to 

 mechanical Astronomy. The terms "force, attraction, inertia, momen- 

 tum," sent us back into preceding centuries then, just as the terms 

 " composition" and " element" send us back now. 



Nor is it to a small extent that we have thus to double back upon 

 our past advance. Next to Astronomy, Chemistry is one of the most 

 ancient of sciences ; the field of the earliest attempts of man to com- 

 mand and understand nature. It has held men for centuries by a kind 

 of fascination ; and innumerable and endless are the various labors, 

 the failures and successes, the speculations and conclusions, the strange 

 pretences and fantastical dreams, of those who have pursued it. To 

 exhibit all these, or give any account of them, would be impossible ; 

 and for our design, it would not be pertinent. To extract from the 

 mass that which is to our purpose, is difficult ; but the attempt must 

 be made. We must endeavor to analyse the history of Chemistry, 

 so far as it has tended towards the establishment of general principles. 

 We shall thus obtain a sight of generalizations of a new kind, and 

 shall prepare ourselves for others of a higher order. 



