vi PREFACE 



The experiments are selected chiefly for their value in establishing 

 the fundamental principles, and no attempt is made to give a com- 

 plete account of experimental methods. For fuller details the 

 reader is referred to Wiedemann's Die Lehre von der Elektricitat , 

 Graetz's Handbuch der Elcldricit'dt und des Magnetismus, Winkel- 

 mann's Handbuch der Physik, or the Encyclopaedia Uriianmcu^ llth 

 edition. 



The mathematical development is only carried so far as is needed 

 for the account of the experiments described. The aim is to build 

 firmly the foundation on which the mathematical theory may be 

 raised. 



The companion volume is now -it press and will be issued 

 shortly. 



J. II. I 1 . 



