Early electrical transformer consisting of a mahogany base and mahogany top with four steel rods enclosing a stack of copper disks separated by waxed paper. Each disk has a projecting metal tag alternatively painted black or red. The black tags and red tags are connected together, forming two electrical circuits. There is a central sliding core of iron terminating in a large nickel-plated knob. Lucien Gaulard and John Dixon Gibbs (about whom we have no information) patented an electrical distribution system c. 1880 in which an alternating current flowing through a primary circuit of the transformer produced an induced current in a secondary circuit. They arranged the transformers in a series, placed at set intervals in a long circuit (some tens of kilometers of wire long), to obtain the local secondary current for incandescent lamps. In the late nineteenth century, transformers began to play a crucial role in distribution systems for alternating current, which came to replace direct current during the twentieth century.