Not only has Mr. Edison invented an incandescent lamp, but he has also identified his name with a very complete system for producing the light on a large scale to suit both domestic and commercial requirements. In the first place he has invented a peculiar form of dynamo-machine, which when driven at great speed by powerful steam or water engines, produces the electricity in great quantity at some central station. From this centre the current is conveyed by copper wires laid under the streets or over the roofs of the houses, these conductors being tapped of their electric fluid by smaller wires which convey the electricity into the houses, in a way similar to that in which gas is conveyed by small pipes from the larger street mains. In each house is an electric meter, a special invention of Mr. Edison’s, which measures the quantity of electricity which passes through it. This meter is very ingenious, and therefore the principle on which it is based may be described. If a current of electricity be passed through a solution of sulphate of copper, contained in a copper jar, the sulphate solution is decomposed and metallic copper is deposited on the inside of the jar. Now it has been proved by experiment, that the amount of copper deposited is always directly proportional to the strength and duration of the electric current. Mr. Edison’s meter consists of such an arrangement, and he finds that by weighing the copper jar, so as to determine exactly what it has gained in weight through the metallic deposition of the solution it contains, he can accurately calculate in units the amount of electricity that has passed through the meter. By means of this beautiful discovery electricity can be supplied and paid for in a manner very similar to that employed in the case of gas at the present time. Within the building to be illuminated, the electric fluid reaches the lamps along small copper wires, about the thickness of ordinary bell wire, which are covered with a coating of gutta percha to prevent the escape of the electricity, which might cause sparks or even fire, or in any case seriously injure any one who might come in contact with the bare metal, by giving him a very violent if not fatal electric shock. The lamps themselves may be fixed to ordinary gas brackets. Mr. Edison has designed some special ones, and the light can be turned on and off, by means of a tap or button, with as great or even still greater facility than gas.