The opposite takes place when, through the extinction of lamps on the external circuit, the demand for current becomes less. In an experiment made with the transformers, which supply some five hundred electric lamps for the Teatro dal Verone and adjoining houses at Milan from the central electrical station three-quarters of a mile away, the main current was often found to vary from one ampère to thirty-five ampères; it was stated that no variation in the service pressure could be detected, and the lamps burnt with equal brightness whatever the number in use. In the experiments at the Teatro dal Verone each transformer worked its own independent circuit of lamps; but, if the conditions of the different circuits were alike, they could be coupled up together in any manner desired, and thus a group of transformers could become a centre of distribution. THE WESTINGHOUSE SYSTEM. The alternating current system of the Westinghouse Company has come to the front in the United States with extraordinary rapidity, and, although it is not three years since the first plant was erected, at the present time over 190,000 incandescent lamps are operated from a number of central-stations. The fundamental principles of the Goulard system have been retained in the Westinghouse converter; but the manner in which these principles are applied has been greatly modified, while most of the details have undergone a radical change at the hands of the engineers and electricians whose researches have been utilised by the Westinghouse Company. The form of converter as now designed consists of a number of thin sheet-iron plates, shaped like the letter =E=, they are slipped alternately from opposite directions over the primary and secondary coils, which are disposed side by side; the inductive core is, therefore, composed of a mass of detached plates insulated from each other by paper, and forming a discontinuous magnetic circuit. In order to protect the converter from mechanical injury as well as dampness, and also to avoid the possibility of contact with wires carrying currents of high potential, it is enclosed in a cast-iron case or box, made in two parts and adapted to be secured to any convenient support. Fig. 12 is a transverse vertical section of such a converter box, with the converter in position. The terminals of the primary coil, P, of the converter are led into the compartment D¹, and the terminals of the secondary coil into D². The terminals are secured to bolts or couplings, _f f_, mounted upon insulating plates, _e_¹ and _e_². Fusible mica-foils, _g_, and switch plates, _h_ and _i_, with plugs _k_, are provided for protecting and disconnecting the circuits. The open front of the compartments D¹ and D² are closed by glass plates, T, which permit inspection of the connections without entering the box. The converter box occupies little space, and may be placed in any convenient situation in or about the premises to be lighted, much the same as a gas-meter.