The use of so-called ``artificial lines''¿i. e. miniature models of electric circuits¿for experimental laboratory studies of transmission-line phenomena is well known. The miniature models are commonly made so as to represent, in true proportion, the electrical constants of a real line. Thus there are artificial telephone lines, artificial submarine cables, artificial long-distance power-transmission lines, etc. A miniature line is a true model of a real line to the extent that the miniature circuit has, for any desired degree of approximation, the same electrical behavior as the full-size circuit. Such laboratory models frequently permit ¿far more conveniently than the full-size circuit¿the study of actual circuit phenomena in a practical and efficient manner. When their limitations are properly understood, miniature circuits may be of great value to transmission-line and operating engineers. Miniature electric circuits may for the present purpose be divided into two general classes: (1) Miniature circuits intended for the study of problems on long lines, such as lines having continuously distributed circuit constants. (2) Miniature circuits for the solution of problems involving complete system networks, inclusive of generating-station and substation apparatus. The following paper deals with a three-phase miniature a-c. system of the network type. The circuit includes synchronous machines, transformers, adjustable resistors, reactors, and condensers, for complete representation of generating stations, substations, lines and loads. The circuit connections are variable, so that any system having not more than the available number of circuit elements may be represented for the correct experimental solution of low-frequency problems.