knew how deep it was; and it was mysterious, too, that

This was truly an altogether prodigious undertaking. We need not wonder that Professor Tyndall, in words implying grave doubt as to the possibility of any solution of the various problems, said publicly that he would much rather have the matter in Edison's hands than in his own. There were no precedents, nothing upon which to build or improve. The problems could only be answered by the creation of new devices and methods expressly worked out for their solution. An electric lamp answering certain specific requirements would, indeed, be the key to the situation, but its commercial adaptation required a multifarious variety of apparatus and devices. The word "system" is much abused in invention, and during the early days of electric lighting its use applied to a mere freakish lamp or dynamo was often ludicrous. But, after all, nothing short of a complete system could give real value to the lamp as an invention; nothing short of a system could body forth the new art to the public. Let us therefore set down briefly a few of the leading items needed for perfect illumination by electricity, all of which were part of the Edison programme:

First--To conceive a broad and fundamentally correct method of distributing the current, satisfactory in a scientific sense and practical commercially in its efficiency and economy. This meant, ready made, a comprehensive plan analogous to illumination by gas, with a network of conductors all connected together, so that in any given city area the lights could be fed with electricity from several directions, thus eliminating any interruption due to the disturbance on any particular section.

Second--To devise an electric lamp that would give about the same amount of light as a gas jet, which custom had proven to be a suitable and useful unit. This lamp must possess the quality of requiring only a small investment in the copper conductors reaching it. Each lamp must be independent of every other lamp. Each and all the lights must be produced and operated with sufficient economy to compete on a commercial basis with gas. The lamp must be durable, capable of being easily and safely handled by the public, and one that would remain capable of burning at full incandescence and candle-power a great length of time.

Third--To devise means whereby the amount of electrical energy furnished to each and every customer could be determined, as in the case of gas, and so that this could be done cheaply and reliably by a meter at the customer's premises.

Fourth--To elaborate a system or network of conductors capable of being placed underground or overhead, which would allow of being tapped at any intervals, so that service wires could be run from the main conductors in the street into each building. Where these mains went below the surface of the thoroughfare, as in large cities, there must be protective conduit or pipe for the copper conductors, and these pipes must allow of being tapped wherever necessary. With these conductors and pipes must also be furnished manholes, junction-boxes, con- nections, and a host of varied paraphernalia insuring perfect general distribution.

Fifth--To devise means for maintaining at all points in an extended area of distribution a practically even pressure of current, so that all the lamps, wherever located, near or far away from the central station, should give an equal light at all times, independent of the number that might be turned on; and safeguarding the lamps against rupture by sudden and violent fluctuations of current. There must also be means for thus regulating at the point where the current was generated the quality or pressure of the current throughout the whole lighting area, with devices for indicating what such pressure might actually be at various points in the area.

Sixth--To design efficient dynamos, such not being in existence at the time, that would convert economically the steam-power of high-speed engines into electrical energy, together with means for connecting and disconnecting them with the exterior consumption circuits; means for regulating, equalizing their loads, and adjusting the number of dynamos to be used according to the fluctuating demands on the central station. Also the arrangement of complete stations with steam and electric apparatus and auxiliary devices for insuring their efficient and continuous operation.

Seventh--To invent devices that would prevent the current from becoming excessive upon any conductors, causing fire or other injury; also switches for turning the current on and off; lamp-holders, fixtures, and the like; also means and methods for establishing the interior circuits that were to carry current to chandeliers and fixtures in buildings.