The present Treatise is based on the Course of Lectures which the Council of the Society of Arts requested the Author to deliver in January and February 1893. In republishing them under less stringent limitations of time and space many gaps have been filled up and some questions have been discussed more fully. The importance of the problem of distributing power to many consumers can hardly be overrated. In dealing with it the question of cost cannot be put on one side. The financial condi tions are governing conditions, and must be considered together with the mechanical conditions. An attempt has been made in the present treatise to treat the subject as a whole. Hence the causes of waste in generating power have been discussed as well as the losses in distribution. The subject is so wide and touches so many departments of engineering that it is too much to hope that all the questions involved have been examined with sufficiently adequate knowledge.