by means of electricity.  Soon afterward the foundry of Ducommun & Co., of Mulhouse, was similarly lighted.  In the course of the following year the apparatus for lighting, by means of carbon candles was introduced into many of the principal factories of France and other leading countries of Europe.  It may prove of interest in this connection to sketch briefly the principal features of the electric light system, and to trace the development of that system in our own and other countries.

Lighting by electricity is accomplished in several ways.  In general, however, the principle by which the result is accomplished is one, and depends upon the resistance which the electrical current meets in its transmission through various substances.  There are no perfect conductors of electricity.  In proportion as the non-conductive quality is prevalent in a substance, especially in a metal, the resistance to the passage of electricity is pronounced, and the consequent disturbance among the molecular particles of the substance is great.  Whenever such resistance is encounted in a circuit, the electricity is converted into heat, and when the resistance is great, the heat is, in turn, converted into light, or rather the heat becomes phenomenal in light; that is, the substance which offers the resistance glows with the transformed energy of the impeded current.  Upon this simple principle all the apparatus for the production of electric light is produced.

Among the metallic substances, the one best adapted by its low conductivity to such resistance and transformation of force, is platinum.  The high degree of heat necessary to fuse this metal adds to its usefulness and availability for the purpose indicated.  When an electrical current is forced along a platinum wire too small to transmit the entire volume, it becomes at once heated—­first to a red, and then to a white glow—­and is thus made to send forth a radiance like that of the sun.  Of the non-metallic elements which offer similar resistance, the best is carbon.  The infusibility of this substance renders it greatly superior to platinum for purposes of the electric light.

Near the beginning of the present century it was discovered by Sir Humphry Davy that carbon points may be rendered incandescent by means of a powerful electrical current.  The discovery was fully developed in the year 1809, while the philosopher just referred to was experimenting with the great battery of the Royal Institution of London.  He observed—­rather by accident than by design or previous anticipation—­that a strong volume of electricity passing between two bits of wood charcoal produces tremendous heat, and a light like that of the sun.  It appears, however, that Davy at first regarded the phenomenon rather in the nature of an interesting display of force than as a suggestion of the possibility of turning night into day.