All About Inventions and Discoveries
The Romance of modern scientific and mechanical Achievements

234 All About Inventions very radically from its consorts both in general design, the tone of the light, and principle of operation. It comprises a long glass tube from which the air is exhausted, and to each end of which a platinum electrode is attached. At one end of this tube is a small bath of mercury which throws off mercury vapour continuously. There is no filament or wire passing through the tube, but the current passes through the vapour, which acts as a conductor, and is induced to glow with a powerful light. The feature of this form of electric illumination is the absence of the red rays in light which prove so inimical to the eyesight. Consequently the light, although powerful and brilliant, is yet soft, of a rich bluish hue, and remarkably restful. It certainly constitutes an ideal illuminant for general and commercial offices, as well as reading-rooms, but cannot be employed in any buildings and trades where colour comparison constitutes part and parcel of the business, the absence of the red rays bringing about strange distortions of colours. Thus objects which appear to be yellow in daylight assume a greenish tinge when viewed in the glow of the mercury lamp. On the other hand, this lamp has the advantage of being economical in the consumption of electric current, this being from one-seventh to one-eighth per candle-power of the obsolete carbon lamp. Between thirty and fifty years ago inventors were striving might and main to achieve the apparently impossible—the “subdivision of the electric light.” Now it would seem as if investigators were endeavour»- ing to resolve the two distinct branches into one again. The new lamp, which has been evolved in the labora-