Inventors in America were not idle. By the close of 1878, Brush, of Cleveland, had brought out his series system of arc lights, including special dynamos, lamps, etc., and by the middle of 1879 had in operation machines each capable of maintaining sixteen arc lamps on one wire. This was, indeed, a great achievement for that time. Weston, of Newark, had also in operation circuits of arc lamps, and the Thomson-Houston system had just started in commercial work with eight arc lamps in series from a single dynamo. Maxim and Fuller, in New York, were working arc lamps from their machines, and capital was being rapidly invested in new enterprises for electric lighting. Some of the great electric manufacturing concerns of to-day had their beginning at that time. Central lighting stations began to be established in cities, and the use of arc lights in street illumination and in stores grew rapidly. More perfect forms of arc lamps were invented, better generating dynamos and regulating apparatus brought out. Factories for arc-light carbon making were built. The first special electrical exhibition was held in Paris in 1881. In the early 80’s, also, the business of arc lighting had become firmly established, and soon the bulk of the work was done under two of the leading systems. These were afterwards brought together under one control, thus securing in the apparatus manufactured a combination of the good features of both. Until about 1892 nearly all the arc lamps in use were worked under the series system, in which the lights are connected one after another on a circuit and traversed by the same current. This current has a standard value, or is a constant current. Sometimes as many as a hundred lamps were on one wire. As the mains for the supply of incandescent lamps at constant pressure, or potential, were extended, attention was more strongly turned to the possibility of working arc lights therefrom.