During several recent years the author has given courses of lectures at three technical schools in London, on the subject of the design of electric machinery. These three schools were: the Northampton Institute of Technology; Faraday House; and University College. Various methods of procedure were employed and these ultimately developed into a general plan which (so far as it related to the subjects of Polyphase Generators and Polyphase Motors), has been followed in the present treatise. It was the author's experience that the students attending his lectures took an earnest interest in calculating designs of their own, in parallel with the working out of the typical design selected by the author for the purpose of his lectures. At the outset of the course, each member of the class was assigned the task of working out a design for a stipulated rated output, speed and pressure. Collectively, the designs undertaken by the class, constituted a series of machines, and co-operation was encouraged with a view to obtaining, at the conclusion of the course of lectures, a set of consistent designs. If a student encountered difficulty or doubt concerning some feature of his design, he was encouraged to compare notes with the students engaged in designing machines of the next larger and smaller ratings or the next higher and lower speeds. Ultimately the results for the entire group of designs were incorporated in a set of tables of which each student obtained blue prints.<br><br>At two of these colleges, the "sandwich" system was in operation, that is to say, terms of attendance at the college were "sandwiched" with terms during which the student was employed in an electrical engineering works.