vi flntro&uctfon. 



If Vol. I is at hand, please read the Intro- 

 duction. It will bring you into closer sym- 

 pathy with the author and his mode of treat- 

 ment. 



Again, if the reader is especially interested 

 in the theory of Electricity it will help him 

 very much if he first reads Vols. I and II, as 

 a preparation for a better understanding of 

 Vol. III. All the natural sciences are so 

 closely related that it is difficult to get a clear 

 insight into any one of them without at 

 least a general idea of all the others. 



