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 employed 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, Ncad and Deschanel, from whose excellent works valuable assistance has been obtained, though he has felt compelled to dissent from some of their views.