From the beginning of his experiments on the electric light Edison had one idea ever in mind, and that was to develop a system of lighting cities from central stations. His plan was to supply electric light and power in much the same way that gas is furnished. He never forsook this idea for a moment. Indeed, it formed the basis of all his plans, although the scientific experts of the time predicted utter failure. While the experiments were going on at Menlo Park he had Mr. Upton and others at work making calculations and plans for city systems. Soon after he had invented the incandescent lamp he began to take definite steps toward preparing for the first central station in the city of New York. After some consideration, he decided upon the district included between Wall, Nassau, Spruce and Ferry Streets, Peck Slip and the East River, covering nearly a square mile in extent. He sent into this district a number of men, who visited every building, counted every gas-jet and found out how many hours per day or night they were burned. These men also ascertained the number of business houses using power and how much they consumed. All this information was marked in colored inks on large maps, so that Edison could study the question with all the details before him. All this work had taken several months, but, with this information to guide him, the main conductors to be laid in the streets of this district were figured, block by block, and the results were marked upon the maps. It was found, however, that the quantity of copper required for these conductors would be exceedingly large and costly, and, if ever, Edison was somewhat dismayed. This difficulty only spurred him on to still greater effort. Before long he solved the problem by inventing the "feeder and main" system, for which he signed an application for patent on August 4, 1880. By this invention he saved seven-eighths of the amount of copper previously required. So the main conductors were figured again, at only one-eighth the size they were before, and the results were marked upon enormous new maps which were now prepared for the actual installation. It should be remembered that from the very start Edison had determined that his conductors should be placed underground. He knew that this was the only method for permanent and satisfactory service to the public. Our young readers can scarcely imagine the condition of New York streets at that time. They were filled with lines of ugly wooden poles carrying great masses of telegraph, telephone, stock ticker, burglar alarm and other wires, in all conditions of sag and decay. The introduction of the arc-lamp added another series of wires which with their high potentials carried a menace to life. Edison was the first to put conductors underground, and the wisdom of so doing became so clear that a few years later laws were made compelling others to do likewise.