A Standard of Light

Abstract

value of the C. G. S. system of absolute physical units, and a recogni tion of the relations between work and heat, and electrical energy. The solidification point of platinum may be a fixed point in nature ; but it has not been shown how this fixed point can be connected with that great web of physical measurements which has been woven by Weber, Helmholtz, Thomson, Maxwell, and other physicists. It is true that during the discussions of the Conference reference was made to a proposition of Schwendler, that the light emitted by a strip of platinum rendered incandescent by a known electrical current should be taken as a standard. This proposition, however, received little support ; and the Conference finally adopted the light emitted by solidifying platinum as a standard. It seems highly desirable that any standard of light which may be adopted should be connected with the present system of absolute measurements. The suggestion of Schwendler, therefore, seems to merit more attention than it has received. The suggestion of employ ing the light from a strip of platinum rendered incandescent by an electrical current is really due to Dr. John W. Draper, of New York, who in 1847 enunciated it as follows: surface of platinum of standard dimensions raised to a standard temperature by a voltaic current will always emit a constant light. A strip of that metal one