In 1896 there came a most revolutionary change in switchboards. All things were made new. Instead of individual batteries, one at each telephone, a large common battery was installed in the exchange itself. This meant better signalling and better talking. It reduced the cost of batteries and put them in charge of experts. It established uniformity. It introduced the federal idea into the mechanism of a telephone system. Best of all, it saved FOUR SECONDS ON EVERY CALL. The first of these centralizing switchboards was put in place at Philadelphia; and other cities followed suit as fast as they could afford the expense of rebuilding. Since then, there have come some switchboards that are wholly automatic. Few of these have been put into use, for the reason that a switchboard, like a human body, must be semi-automatic only. To give the most efficient service, there will always need to be an expert to stand between it and the public. As the final result of all these varying changes in switchboards and signals and batteries, there grew up the modern Telephone Exchange. This is the solar plexus of the telephone body. It is the vital spot. It is the home of the switchboard. It is not any one's invention, as the telephone was. It is a growing mechanism that is not yet finished, and may never be; but it has already evolved far enough to be one of the wonders of the electrical world. There is probably no other part of an American city's equipment that is as sensitive and efficient as a telephone exchange. The idea of the exchange is somewhat older than the idea of the telephone itself. There were communication exchanges before the invention of the telephone. Thomas B. Doolittle had one in Bridgeport, using telegraph instruments Thomas B. A. David had one in Pittsburg, using printing-telegraph machines, which required little skill to operate. And William A. Childs had a third, for lawyers only, in New York, which used dials at first and afterwards printing machines. These little exchanges had set out to do the work that is done to-day by the telephone, and they did it after a fashion, in a most crude and expensive way. They helped to prepare the way for the telephone, by building up small constituencies that were ready for the telephone when it arrived.