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

232 All About Inventions even in this field. Improvement after improvement was effected, each of which exerted some decided influence upon this form of illumination. For many years plain carbons were used, the light from which was bluish-white in colour. Subsequently calcium fluoride was combined with the carbon, the light from which is a rich warm orange or rose-coloured tint. Another contribution to the science was that evolved by Professor Steinmetz, who discovered that mag- netite, or lodestone, is superior to carbon, its efficiency being twice as great; and this led to what is known as the magnetite arc-lamp. In describing the incandescent electric lamp, I have related how the filament is placed in a glass bulb from which the air is exhausted. For many years the investigators concentrated their energies upon extracting as much air as possible from the globe. Upon the perfection of the metallic filament lamp the line of research veered round completely. A number of scientists concluded that a far brighter light, with a proportionately lower consumption of electric current, might be obtained if the glass globe were first exhausted of air and then charged with one of the inert gases, of which nitrogen is the most familiar. Various gases of this character were submitted to the test, from the most rare and expensive to the cheapest and most readily obtainable. As the result of several years’ patient and diligent research an entirely new lamp was produced, in which the fila- ment is raised to incandescence by the passage of . the electric current in an atmosphere of nitrogen. The globe is first exhausted of atmospheric air, to