The great importance of the "Feeder" and "Three-wire" inventions will be apparent when it is realized that without them it is a question whether electric light could be sold to compete with low-priced gas, on account of the large investment in conductors that would be necessary. If a large city area were to be lighted from a central station by means of copper conductors running directly therefrom to all parts of the district, it would be necessary to install large conductors, or suffer such a drop of pressure at the ends most remote from the station as to cause the lights there to burn with a noticeable diminution of candle-power. The Feeder invention overcame this trouble, and made it possible to use conductors ONLY ONE-EIGHTH THE SIZE that would otherwise have been necessary to produce the same results. A still further economy in cost of conductors was effected by the "Three-wire" invention, by the use of which the already diminished conductors could be still further reduced TO ONE-THIRD of this smaller size, and at the same time allow of the successful operation of the station with far better results than if it were operated exactly as at first conceived. The Feeder and Three-wire systems are at this day used in all parts of the world, not only in central-station work, but in the installation and operation of isolated electric-light plants in large buildings. No sensible or efficient station manager or electric contractor would ever think of an installation made upon any other plan. Thus Mr. Edison's early conceptions of the necessities of a complete system, one of them made even in advance of practice, have stood firm, unimproved, and unchanged during the past twenty-eight years, a period of time which has witnessed more wonderful and rapid progress in electrical science and art than has been known during any similar art or period of time since the world began. It must be remembered that the complete system in all its parts is not comprised in the few of Mr. Edison's patents, of which specific mention is here made. In order to comprehend the magnitude and extent of his work and the quality of his genius, it is necessary to examine minutely the list of patents issued for the various elements which go to make up such a system. To attempt any relation in detail of the conception and working-out of each part or element; to enter into any description of the almost innumerable experiments and investigations that were made would entail the writing of several volumes, for Mr. Edison's close-written note-books covering these subjects number nearly two hundred.