A unit of luminous intensity, late 19th – early 20th centuries, the light emitted by 1 square centimeter of glowing platinum at the temperature at which it freezes. About 20 candlepower.
Jules Louis Gabriel Violle (1841-1923),
a French physicist, first proposed using as a light
standard the incandescence of a metal at the temperature at which it freezes on 21 September 1881 at the International Conference of Electricians in
Paris.1
On 16 October 1882, a group of more than 47 distinguished physicists met at the residence of the French foreign minister in Paris, as an “International Conference for the Determination of the Electrical Units.” A committee was formed to discuss a standard for light. After several proposals were considered,
“Dumas2 suggested that the late experiments of Violle upon the light emitted by melting platinum might solve the problems. The point of fusion of a body seemed to him to be as good a fixed point as could be wished. He invited the commission to view the experiments of Violle.
“After witnessing the experiments of Violle, the members of the commission appeared to think more favorably of Dumas’ suggestion.”3
Before adjourning on 26 October 1882, the conference passed a resolution:
“The conference express their hope that the experiments now in process upon the light emitted by melting platinum will lead to a definite standard of light.”3
Violle published the results of his experiments on the use of a platinum radiator at this temperature as a standard of luminous intensity in 1884,4 and in the same year it was adopted as a unit by the International Conference for the Determination of the Electrical Units:
L'unité de chaque lumière simple est la quantité de lumière de même espèce émise en direction normale par un centimètre carré de surface de platine fondu, à la température de solidification. L'unité pratique de lumière blanche est la quantité totale de lumière émise normalement par la même source.5
The unit of each type of simple light is the quantity of light of the same kind emitted perpendicular to a square centimeter of molten platinum at the temperature at which it solidifies. The practical unit of white light is the total quantity of light emitted perpendicular to the same source.
The unit was reconfirmed at the International Conference of Electricians (Paris, 21 May 1889), the International Congress (Chicago, 1893), and the International Conference of Electricians (Geneva, 1896).
1. Comptes Rendus du Congrès International des Electriciens, Paris, 1881. Assemblée générale, Troisème Séance, page 50.
2. Jean Baptiste André Dumas (1800 – 1884).
3. The International Conference for the Determination of the
Electrical Units. here
Science, volume 1, no. 4, pages 87-89 (2 March 1883).
For the proceedings in French, see: Procès-Verbaux de la Conférence Internationale pour la Détermination des Unités Électriques, Troisième Commission, Séance du 20 Octobre, 1882, page 131.
4. J. Violle.
On the Absolute Standard of Light.
Philosophical Magazine and Journal of Science, series 5, volume 17, page 563 (1884).
Translated from the Comptes Rendus of 28 April 1884.
or
Annales de Chimie et de Physique, series 6, volume 3, page 373 (1884).
or
Conférence Internationale pour la Détermination des Unités
Électriques, séance de la Troisième Commission, 3 April 1884.
5. Procès-Verbaux de la Conférence Internationale pour la Détermination des Unités Électriques. Deuxième Session, Troisième Séance, 2 May 1884.
6.
C. W. Waidener and G. K. Burgess.
Comptes Rendu Academy Sci (France), volume 148, page 1117 (1909).
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