114 HISTORY OF GALVANISM. 



in all other branches of knowledge, the meaning of 

 words is to be sought in the progress of thought ; 

 the history of science is our dictionary; the steps 

 of scientific induction are our definitions. It is 

 only by going back through the successful researches 

 of men respecting the composition and elements of 

 bodies, that we can learn in what sense such terms 

 must be understood, so as to convey real know- 

 ledge. In order that they may have a meaning 

 for us, we must inquire what meaning they had 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 mechanical 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 me- 

 chanics, before we could proceed to mechanical 

 astronomy. The terms "force, attraction, inertia, 

 momentum," 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 command and understand nature. It has 



