VI PREFACE. 



so happily developed by Clerk Maxwell, on the conside- 

 ration of the lines of force, and on the function of the 

 medium in which electrical and magnetic actions are exerted. 

 This conception brilliantly elucidates the relations between 

 various phenomena, and has given rise to a totally unfore- 

 seen theory of light. 



As our principal aim was to be of service to physicists, 

 we have made all efforts to simplify the demonstrations 

 without in any way sacrificing the strictness of the reasoning. 

 Those parts which require a somewhat more advanced 

 analysis, and which can be readily distinguished, may be 

 omitted in a first reading; in most cases they are not in- 

 dispensable for following the development of theory. 



In the last few years the science of electricity has under- 

 gone a real transformation ; we eagerly recognise our nu- 

 merous obligations to the works of those physicists who 

 have most contributed to this reform, and particularly to 

 the memoirs of Sir W. Thomson, and the excellent treatise 

 of Clerk Maxwell. 



In this English edition we have introduced several 

 corrections, and have given some new proofs of certain 

 questions. We must express our obligations to Dr. At- 

 kinson for the care and exactitude with which the trans- 

 lation has been made. 



