220 PEOCEEDINGS OF THE AMERICAN ACADEMY 



Intibtigations on Light and Heat, made and pubushed wholly or dj paet with 

 Appropeiation from the Rumford Fdnd. 



IX. 



CONTEIBUTIONS FROM THE PHYSICAL LABORATORY OF THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XXVL — EXPERIMENTS ON THE MELTING PLATINUM 

 STANDARD OF LIGHT. 



By Charles R. Cross. 



Presented June 16, 1886. 



Notwithstanding the fact that the amount of light emitted normally 

 by a square centimeter of platinum at its point of solidification has 

 been adopted as a standard both by the International Electrical Con- 

 ference and by the United States National Conference of Electricians, 

 but very few experiments have been made to determine whether it can 

 be made reliable and capable of practical use. An approach toward 

 giving the method a practical form was made by W. Siemens,* who 

 proposed to substitute the light emitted by a given area of platinum at 

 its melting point instead of at its point of solidification, and suggested 

 a means by which with this modification the standard could readily be 

 utilized. 



The following experiments resulted from a conference of a portion 

 of the Committee on Standards of Light appointed at the Electrical 

 Conference at Philadelphia in 1884.t They had for their object the 

 ascertaining of a single fact, viz. the amount of the average deviation 

 which would arise in a series of measurements of the light emitted by a 

 strip or wire of platinum of given surface when at the melting point. 



A few preliminary experiments were made by the writer, in which 

 a measured length of fine platinum wire, four one-thousandths of an 

 inch in diameter, was placed at one end of the bar of a Bunsen pho- 

 tometer, with a gas-jet shining through a limited aperture at the other 

 end. A current from a small hand Gramme machine was carried 

 through the wire, which was made to glow more and more brilliantly 



* Wied. Ann., 1884, vol. xxii. p. 304. 



t Messrs. J. Trowbridge, E. C. Pickering, and C. R. Cross. 



