INTRODUCTION. 



Of the Meclianico-Chemical Sciences. 



TTNDERthe title of Mechanico-ChemicalSciences> 

 VJ 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 physical knowledge ; and not the 

 least of the circumstances which give them their 

 interest, is that double bearing upon mechanical 

 and chemical principles, which their name is in- 

 tended to imply. Indeed, at first sight they appear 

 to be purely Mechanical Sciences ; the attractions 

 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 mag- 

 netism 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 altogether different. Mag- 

 netism is associated with Electricity by its mecha- 

 nical analogies ; and, more recently, has been 

 discovered to be still more closely connected with 

 it by physical influence; electric is identified with 



