INTRODUCTION. 



Of tJie Meclianico- Chemical Sciences. 



UNDER the title of Mechanico-Chemical Sciences, I include the 

 laws of Magnetism, Electricity, Galvanism, and the other classes 

 of phenomena closely related to these, as Thermo-electricity. This 

 group of subjects forms a curious and interesting portion of our phy- 

 sical knowledge ; and not the least of the circumstances which give 

 them their interest, is that double bearing upon mechanical and che- 

 mical principles, which their name is intended to imply. Indeed, at 

 first sight they appear to be purely Mechanical Sciences ; the attrac- 

 tions and repulsions, the pressure and motion, which occur in these 

 cases, are referrible to mechanical conceptions and laws, as completely 

 as the weight or fall of terrestrial bodies, or the motion of the moon 

 and planets. And if the phenomena of magnetism and electricity had 

 directed us only to such laws, the corresponding sciences must have 

 been arranged as branches of mechanics. But we find that, on the 

 other side, these phenomena have laws and bearings of a kind alto- 

 i;vther different. Magnetism is associated with Electricity by its 

 mechanical analogies ; and, more recently, has been discovered to be 

 still more closely connected ttith it by physical influence ; electric is 

 identified with galvanic agency ; but in galvanism, decomposition, or 

 some action of that kind, universally appears; and these appearances 

 lead to very general laws. Now composition and decomposition are 

 the subjects of Chemistry ; and thus we find that we are insensibly 

 but irresistibly led into the domain of that science. The highest 

 generalizations to which w r e can look, in advancing from the elemen- 

 tary facts of electricity and galvanism, must involve chemical notions ; 

 we must therefore, in laying out the platform of these sciences, make 

 provision for that convergence of mechanical and chemical theory, 

 which they are to exhibit as we ascend. 



TVe must begin, however, with stating the mechanical phenomena 

 of these sciences, and the reduction of such phenomena to laws. In 

 this point of view, the phenomena of which we have to speak are 

 those in which bodies exhibit attractions and repulsions, peculiarly 

 determined by their nature and circumstances ; as the magnet, and a 



