The initial hydroelectric development of the Niagara Falls Power Company is referred to and comparisons are made with the latest development, which involves three units, each with a 65,000-kv-a. generator. The amount of material in a generator as affected by speed, periodicity and efficiency aimed at, is discussed. The electrical characteristics of the first of the 65,000-kv-a. generators are outlined. The mechanical construction is described in considerable detail with the aid of cross-sectional views of certain parts and of the generator as a whole. A special feature of this unit is a direct-connected 650-kv-a., 25-cycle generator for furnishing excitation through a motor-generator set and for driving auxiliaries, such as pumps. Some weight data are added, showing this generator to contain over one and one-half million pounds of material-undoubtedly the heaviest electrical machine ever built.