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

236 All About Inventions osity of the electric arc with the advantages, conveni- ence, and safety of the incandescent filament lamp. While the electric light is extensively utilised for general and varied illuminating purposes, this by no means exhausts its spheres of usefulness. It is being widely employed for medical purposes, especially in the treatment of certain skin diseases such as tuber- cular lupus. The best known and most successful of these is that perfected by Dr. Finsen, who contrived a special lamp for the purpose. The light is very powerful, and is particularly rich in the ultra-violet rays, which are of distinct therapeutic value. The Crookes tube, which is employed in connection with X-ray photography, is another type of electric lamp designed to fulfil a specific duty. The electric light has also been discovered to possess first-class sterilising properties, the ultra- violet rays being fatal to microbic life. The lamps are of special design, so as to secure the maximum intensity of the necessary rays, and the water is passed before the light in a thin sheet or veil. The most deadly germs succumb instantly to the action of these rays, and the most heavily contaminated water can be speedily and cheaply sterilised by this process. Simple installations operating on this system are obtainable for use in the ordinary home, while it may be elaborated to meet the exacting and heavy demands of a densely populated town or city with equal suc- cess. Indeed, several plants have been laid down upon the Continent, upon which the citizens depend exclusively upon the germ-destroying properties of the ultra-violet rays in electric light, adapted to the purpose, for their pure drinking water.