Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. As to the mode of treatment I have adopted, a few words are necessary. The book is not a treatise on the mathematical theory of electricity merely, but is, I hope, to some extent successful in bringing the theory and practice together. Thus while in general assuming some elementary acquaintance on the part of the reader with electrical phenomena and their laws, I have endeavoured first to look at the phenomena as they present themselves, and then to show how they fall into their places in the general scheme of electrical action, and to point out the consequences to which they lead. As stated in the words of Bacon I have placed on the title-page, it is a double process by which natural philosophy advances; we ascend from experiments to causes, and descend from causes to experiments, and it is most requisite that these two parts be severally considered and handled.