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. IN preparing this new edition a number of minor alterations have been made and several subjects introduced which were not dealt with in the earlier editions. Among these may be mentioned the differential booster and the automatic voltage regulation of alternators. The sections dealing with single-phase commutator motors have been extended and rewritten. Descriptions of machines of obsolete types have been omitted.