Image of a Westinghouse circuit breaker. Around the time of the publication of the book (1901), large numbers were in use and gave very good service. a and b are the main contacts. c is the crosspiece that a and b are connected to. The current flows from a to c to b, which trips the coil d and exits out l. m is an auxiliary carbon contact, n is a carbon wiper, and w is an adjustable weight attached to the armature.
International Correspondence Schools A Textbook on Electric Lighting and Railways (Scranton, PA: International Textbook Company, 1901)