The chief purpose of this book is to give the methods, which many years of experience have proved to be both simple and effective, for tracing and remedying direct current motor and generator troubles. In addition, the questions of the selection, operation, care and repair of direct current machinery are analyzed from the standpoint of the operator.<br><br>The theories of why a motor or generator will run, as well as the problems and fundamentals underlying the design of direct current machinery, have been very completely given and expounded in numerous excellent books on the market. But it is our belief that there is a vast army of operators in the electrical world who are greatly interested in why the motor or generator will not run, and it is to supply information on this topic that the present work has been written. Throughout, it is assumed that the operator is confronted with the question of selection of the best machine for his purpose; then with the question of the best operation of that machine and in case of troubles, with their tracing and effective remedying.<br><br>In all cases, an effort has been made to treat the subjects in as general a way as possible so as to include all methods in good practice. Standard machines are described and illustrated so as to in no way limit and restrict the information to the operation of special types. We are greatly indebted to the General Electric Company, the Westinghouse Electric Manufacturing Company, and the Allis-Chalmers Company for their kindness in furnishing the illustrations for this publication.