ELEC PREFACE IN undertaking the present work, our first idea was simply to translate M. Joubert's Traité élémentaire d'Électricité, perhaps introducing such small modifications as might seem to make it better adapted to English requirements. But, on further consideration, we decided, while adhering to the general plan and scope of the original, to endeavour to introduce into it that view of the nature of electrical phenomena which was originated by Faraday and developed by Maxwell in his classical Treatise. Although these views have now for some years formed the starting-point of almost all the greatest forward steps in electrical science, they have not yet, so far as we are aware, been adopted as the basis of a systematic exposition of so elementary a kind as the present. The endeavour to carry out this idea implied the keeping in view, from the beginning, of the dual character of electrification, and the emphasising of the essential part played in the most familiar electrical phenomena by the dielectric medium in which they occur. This led to the early introduction of the idea of lines and tubes of force, and involved the rewriting of several chapters or parts of chapters. the discussion of Electrostatic Capacity and Energy (see especially Chapter VI.), it seemed to be more in harmony with the general point of view indicated above to speak of charge, capacity, and energy as belonging to the electric field as a whole, rather than to the conductors which form its boundaries. In |