This is called the _multiple_ circuit, and it is obvious that the entire amperage produced by the dynamo will not be required to pass through each lamp, but, on the other hand, each lamp takes only enough necessary to render the filament incandescent. This invention at once solved the problem of the incandescent system and was called the subdivision of the electric light. By this means the cost was materially reduced, and the wiring up and installation of lights materially simplified. But the divisibility of the light did not, by any means, solve the great problem that has occupied the attention of electricians and experimenters ever since. The great question was and is to preserve the little filament which is heated to incandescence, and from which we get the light. The effort of the current to pass through the small filament meets with such a great resistance that the substance is heated up. If it is made of metal there is a point at which it will fuse, and thus the lamp is destroyed. It was found that carbon, properly treated, would heat to a brilliant white heat without fusing, or melting, so that this material was employed. But now followed another difficulty. As this intense heat consumed the particles of carbon, owing to the presence of oxygen, means were sought to exclude the air. This was finally accomplished by making a bulb of glass, from which the air was exhausted, and as such a globe had no air to support combustion, the filaments were finally made so that they would last a long time before being finally disintegrated. The quest now is, and has been, to find some material of a purely metallic character, which will have a very high fusing point, and which will, therefore, dispense with the cost of the exhausted bulb. Some metals, as for instance, osmium, tantalum, thorium, and others, have been used, and others, also, with great success, so that the march of improvements is now going forward with rapid strides. VAPOR LAMPS.--One of the directions in which considerable energy has been directed in the past, was to produce light from vapors. The Cooper Hewitt mercury vapor lamp is a tube filled with the vapor of mercury, and a current is sent through the vapor which produces a greenish light, and owing to that peculiar color, has not met with much success. It is merely cited to show that there are other directions than the use of metallic conductors and filaments which will produce light, and the day is no doubt close at hand when we may expect some important developments in the production of light by means of the Hertzian waves. DIRECTIONS FOR IMPROVEMENTS.--Electricity, however, is not a cheap method of illumination. The enormous heat developed is largely wasted. The quest of the inventor is to find a means whereby light can be produced without the generation of the immense heat necessary.