Vlll PREFACE. 



great enough without being mixed up with mathematical ones. 

 It is also a pity to have the student get the idea that certain 

 theorems pertain to electricity, when they really are simply 

 matters of geometry or analysis. I have whenever possible at- 

 tempted to bring out the geometrical or physical nature of the 

 processes involved before coming to the electrical application. 

 Thus these introductory chapters may serve as a sort of general 

 introduction to Mathematical Physics. 



After a treatment of the problem of Electrostatics in a single 

 medium by means of the Principle of Virtual Work the usual 

 methods of attacking electrostatic problems are treated. These 

 chapters pertain to either the new or the old theory. I have 

 then inserted the chapter on Electrokinetics, somewhat out of its 

 natural order, in order to bring out the geometrical ideas involved 

 in the so-called Law of Ohm. Of these application is made in 

 the treatment of Dielectrics and Magnetizable Bodies, which is 

 carried out in such a manner as to show the close parallelism 

 between the two classes of phenomena there treated, a point not 

 always insisted on by Maxwell, but clearly brought out by Hertz 

 and Heaviside. On account of this the symmetrical notation of 

 Hertz is adopted in preference to that of Maxwell. I have 

 however kept the term induction used by Maxwell for magnetism 

 alone, instead of the term polarization used by Hertz, which I 

 have used in the more usual sense of moment of unit volume. I 

 regret not having been able to respond to the appeal made by 

 Boltzmann to future writers to follow Maxwell's notation. I feel 

 that it is more important to have a good notation than a familiar 

 one, and that it is a first essential of a good notation that it 

 should be symmetrical. The indiscriminate mixture of Greek, 

 Roman and German letters used by Maxwell is as u fortunate 

 as the dissymmetry with respect to electrical and magnetic 

 phenomena. 



It is hardly necessary to say that vector methods have been 

 used throughout, although the abbreviated notation of Hamilton 



