Page:Popular Science Monthly Volume 19.djvu/395

Rh street lamp-posts, one machine working many lights. The former system appears to be the best for symmetrical spaces and large areas, the latter for long and narrow streets and thoroughfares; so, in internal illumination, the central system is preferable for lofty, spacious rooms, the distributed for long and low ones.

An eventful feature in practical lighting is the proper scattering or diffusion of light, by shades, screens, and reflecting surfaces. We want to emulate the diffusion of daylight. It is marvelous how whitewashed surfaces do this. Well-selected globes act as though they were self-luminous; they scatter light and produce shadows. The power of the light, however, to penetrate fogs does not appear to be any greater than that of gaslight. This is because the shorter-waved rays that give the light its violet tint are checked by the vapors, in the same manner as the like rays in the sun are checked, and it is made to appear red. The same cause operates to give the electric light a greater illuminating power in its immediate neighborhood, for the checked rays are reflected back to add their intensity to that of the direct rays.

Nearly three hundred Gramme machines are in use in England generating light; there are many more Siemens machines, and the Brush people have installed many machines and lights. Nearly all the ironclads in the navy are supplied with the electric light. In libraries, while reading by gaslight is irksome, reading by the electric light is simply delightful. Railway-stations are gradually adopting the lights; seaside resorts are illuminating their parades with them. It would be impossible to make any summary of the numerous manufacturing establishments that have been supplied with lights worked successfully.

Notwithstanding these great advances in its use, it must not be forgotten that the electric light has its defects and its disadvantages. The intense shadows that it occasions are troublesome. The unsteadiness of the light is at times wearisome. The hissing which impurities in the carbon and irregularities in the current produce is tantalizing, and the light has an unfortunate habit of misbehaving itself when it is most wanted. Moreover, the problem of durability remains yet to be solved. Many have tried the light and abandoned it. In some cases its economy is unquestionable, but there are places where careful persons have shown that gas, as regards economy, surpasses it. It is questionable whether, in some cases, the electric light does not affect the eye. The arc-light produces, also, nitrous acid and other deleterious gases, but the incandescent lamp is free from this trouble. The powerful currents that it requires can not be carried over buildings and rooms without incurring danger from fire and to life. Nevertheless, the light has great and manifold advantages. The brilliancy of a well-lighted room is simply enchanting. The purity of the light for the transaction of business, the selection of colors, and the ordinary daily avocations of life, is simply superb. Its cleanliness is one of its great merits. It