PREFACE. 



SOME justification is perhaps necessary for the appearance of 

 another treatise on Electricity and Magnetism, in view of the 

 numerous ones already existing in English. This book is the 

 result of a demand encountered in my own experience in teaching, 

 and is based upon various courses of lectures that I have delivered 

 at Clark University during the last six years. The classical treatise 

 of Maxwell, which must always remain as a point of departure 

 for the modern treatment of the subject, is ill adapted to the 

 purpose of a text-book. To ask a student to attempt to assimilate 

 the contents of the two volumes of Maxwell in a year, or even 

 in two years, is only to expose him to the severest pangs of mental 

 indigestion. Again, Maxwell's own views are there presented by 

 him with not the greatest clearness, while severe demands are 

 made upon the student's mathematical attainments. The excel- 

 lent treatises of Mascart and Joubert and of Watson and Burbury 

 follow Maxwell with considerable closeness. Professor Gray's 

 admirable treatise, though containing much recent matter, suffers 

 under the disadvantage of being in three volumes, while the very 

 convenient little book of Mr Emtage is somewhat restricted in 

 scope. Professor J. J. Thomson's altogether delightful Elements 

 of the Mathematical Theory, which appeared when the present 

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