“Look at the furnaces and boilers of a steam-engine driving a group of dynamos, and estimate the energy expended; and then look at the incandescent filaments of the lamps excited by them, and estimate how much of their radiated energy is of real service to the eye. It will be as the energy of a pitch-pipe to an entire orchestra. “It is not too much to say that a boy turning a handle could, if his energy were properly directed, produce quite as much real light as is produced by all this mass of mechanism and consumption of material.”[6] [6] Professor Oliver Lodge, in a lecture to the Ashmolean Society, 3rd June 1889. The most perfect light in nature is probably that of the glow-worm and firefly--a phosphorescent or “cold” light, illuminating without combustion owing to the absence of all waves but those of the requisite frequency. The task before mankind is to imitate the glow-worm in the production of isolated light-waves. The nearest approach to its achievement has occurred in the laboratories of Mr. Nikola Tesla, the famous electrician. By means of a special oscillator, invented by himself, he has succeeded in throwing the ether particles into such an intense state of vibration that they become luminous. In other words, he has created vibrations of the enormous rapidity of light, and this without the creation of heat waves to any appreciable extent. An incandescent lamp, mounted on a powerful coil, is lit _without_ contact by ether waves transmitted from a cable running round the laboratory, or bulbs and tubes containing highly rarefied gases are placed between two large plate-terminals arranged on the end walls. As soon as the bulbs are held in the path of the currents passing through the ether from plate to plate they become incandescent, shining with a light which, though weak, is sufficiently strong to take photographs by with a long exposure. Tesla has also invented what he calls a “sanitary” light, as he claims for it the germ-killing properties of sunshine. The lamps are glass tubes several feet long, bent into spirals or other convolutions, and filled before sealing with a certain gas. The ends of the glass tube are coated with metal and provided with hooks to connect the lamp with an electric current. The gas becomes _luminous_ under the influence of current, but not strictly incandescent, as there is very little heat engendered. This means economy in use. The lamps are said to be cheaply manufactured, but as yet they are not “on the market.” We shall hear more of them in the near future, which will probably witness no more interesting development than that of lighting.