1 V IX TROD UC TWN. 



reserve the consideration of the latter for a separate 

 volume. 



Care has been taken to avoid the introduction of 

 new matter before the student was prepared for it ; 

 hence it was thought best that there should be a 

 thorough examination of elementary principles before 

 introducing complicated apparatus, the construction 

 and operation of which depends on those principles. 



The theory assumed is, that electricity is one of 

 the forms in which energy manifests itself; that its 

 nature is not changed by the means emplo} T ed to 

 generate it, and that the various terms, positive, 

 negative, static, dynamic, express certain conditions and 

 relations in which this manifestation occurs, and 

 not different kinds of electricity. 



The author takes pleasure in acknowledging his 

 obligations to Elisha Gray for the use of tables, giving 

 the results of observations on earth currents, made 

 under his direction on the Postal Telegraph line; also 

 to Ferguson, Gordon, Silvanus P. Thompson, Noad 

 uiicl Deschanel, from whose excellent works valuable 

 assistance has been obtained, though he has felt 

 compelled to dissent from some of their views. 



The views here expressed are the result of many 

 years' experience in the class room, the lecture room, 

 and the laboratory, and were adopted only after the 

 most rigid test of actual and oft repeated experiment. 

 And some of the more important apparatus described 



