VIOLLE, JULES LOUIS GABRIEL

(b. Langres, France, 16 November 1841; d. Fixin, France, 12 September 1923), physics.

Most of Violle’s research consisted of the experimental study of topics associated with heat radiation and with high temperatures, and developed out of Violle’s interest in the temperature of the sun.

Violle entered the École Normale Supérieure in 1861. He became agrégé in 1868, and received the degree of docteur-ès-sciences in 1870. (Violle was already interested in heat; for his thesis he determined the mechanical equivalent of heat by rotating a copper disk between the poles of an electromagnet and measuring calorimetrically the heat produced by the induction currents.¹) Violle taught at the universities of Grenoble and Lyons, and in 1884 he became maître de conférences at the École Normale. In 1892 he became professor of physics at the Conservatoire des Arts et Métiers, and in 1897 he was elected to the French Academy of Sciences. Violle was interested in American science and, after visiting the United States and the World’s Columbian Exposition in Chicago in 1893, he published some discussions of it.²

Early in 1874, in Grenoble, Violle began work on his first major project, the design and use of an actinometer to measure the solar constant and, indirectly, to determine the temperature of the sun. The solar constant had been defined and first measured in 1837 by Pouillet.³ In Violle’s instrument a thermometer is kept in a container at constant temperature, and sunlight is allowed to fall onto the bulb through a small hole. The rise in temperature to an equilibrium value when the hole is opened and the subsequent fall in temperature when the hole is closed again are measured. From this information Violle calculated the initial change in the temperature of the bulb and determined the rate at which heat reaches it.

In order to obtain the solar constant, it is necessary to correct the amount of heat that the instrument actually receives by the amount of heat absorbed by the atmosphere. Before Violle, the atmospheric absorption was found by comparing measurements made at different times of day. violle compared observations made simultaneously at different altitudes. On 16 and 17 August 1875, he took measurements at the top of Mont Blanc, while others were being taken more than 3.5 kilometers below. Violle found an empirical formula for the atmospheric absorption, and concluded that the solar constant was 2.54 cal./cm.²/ minute.

Without a knowledge of the relation between temperature and energy radiation, it was difficult to deduce the solar temperature from the solar constant. (It was not until 1879 that Stefan showed that the energy varies as T⁴, and the proportionality constant was not known until much later.⁴) Violle extrapolated the empirical law of Dulong and Petit. To check on the validity of this extrapolation, Violle used his actionometer to determine the known temperature of molten steel (about 1,000° C). Violle concluded that the effective temperature of the sun is about 1,500° C.

At the time of Violle’s work there was much interest in the temperature of the sun. The Paris Academy had proposed the determination of it as a problem for the Bordin prize in 1874 and in 1876. Because of the problems involved in determining atmospheric absorption and extrapolating the law of Dulong and Petit to high temperatures, Violle’s work received only a recompense and not the actual prize (which was not awarded at all).⁵ Some of the difficulties were solved a few years later by Samuel Pierpont Langley, who showed that the atmospheric absorption varies with frequency, and who designed a bolometer to measure the heat received across the spectrum. When Langley made his first measurements by this method (in 1881, on an expedition to Mt. Whitney), he obtained some of his data with an actinometer sent especially for the purpose by Violle⁶.

As a consequence of the work on solar temperature, Violle became involved in various questions related to the determination of high temperatures. For example, he found the specific heats of platinum, palladium, and iridium up to the highest temperatures that can be measured with a gas thermometer, and then, extrapolating the relationship between specific heats and temperature, he determined their melting points. To learn something about the relation between temperature and radiation, Violle used his actinometer to determine the heat radiation emitted by platinum at various temperatures. He found the rise in energy to be slower than the extrapolation from the law of Dulong and Petit would imply, and also that at high temperatures more of the energy is in the shorter wavelengths. Violle suggested that the light emitted by liquid platinum be used as a photometric standard, and it was adopted by the International Conference on Electrical Units and Standards in 1884.

From about 1885, and continuing for about twenty years, Violle did experiments with Théodore Vautier on the propagation of sound. Violle and Vautier were interested in obtaining an accurate determination of the velocity of sound and in studying various nonlinearities and dispersions in the propagation. They analyzed the propagation of sound along an underground cylindrical pipe built for the Grenoble water system, which provided a path length of more than 12 kilometers. They looked for effects of frequency and amplitude on the velocity and for changes in the form of the disturbance during its propagation.

NOTES

1. “Sur l’équivalent mécanique de la chaleur,” in Annales de chimie, 21 (1870), 64–97.

2. “L’exposition de Chicago et la science américaine,” in Revue des deux mondes, 123 (1894), 579–611; “Court aperçu de l’ètat de l’astronomie aux États-Unis,” in Ciel et terre, 15 (1894-1895), 223–232; “Le mouvement scientifique aux Ëtats-Units,” in Annales du conservatoire des arts et métiers, 6 (1894), 253–313.

3. C. Pouillet, “Mémoire sur la chaleur solaire, sur les pouvoirs rayonnants et absorbants de l’air atmosphérique, et sur la température de l’espace,” in Comptes rendus hebdomadaires des séances de l’ Anadémie des sciences, 7 (1838), 24–65.

4. Max Jammer, The Conceptual Development of Quantum Mechanics (New York, 1966), 6–8.

5.Comptes rendus hebdomadaires des séances de l’Académie des sciences, 84 (1877), 813–817. On the difficulty of determining the solar constant, S.P. Langley wrote the following; “We are as though at the bottom of a turbid and agitated sea, and trying thence to obtain an idea of what goes on in an upper region of light and calm.” Researches on Solar Heat and Its Absorption by the Earth’s Atmosphere (Washington, D. C., 1884), 45.

6. S. P. Langley, ibid., 70.

BIBLIOGRAPHY

I. Original Works. Violle’s papers include “Sur la température du soleil,” in Comptes rendus hebdomadaires des séances de l’Académie des sciences, 78 (1874), 1425-27, 1816-1820; 79 (1874), 746–749; “Mesures actinométriques au sommet du Mont Blanc,” ibid., 82 (1876), 662–665; “Résultats des mesures actinométriques au sommet du Mont Blanc,” ibid., 729–731; “Conclusions des mesures actinométriques faites au sommet du Mont Blanc,” ibid., 896–898; “Chaleur spécifique et chaleur de fusion du platine,” ibid., 85 (1877), 543–546; “Sur la loi de rayonnement,” ibid., 92 (1881), 1204-1206; “Sur la propagation du son ä l’intérieur d’un tuyay cylindrique,” in Annales de chimie et de physique, ser. 6, 19 (1890), 306–345, with Théodore Vautier.

The following works list publications by Violle: “Notice sur les trauvaux scientifiques de M. Jules Violle” (Paris, 1889); Royal Society Catalogue of Scientific Papers, VIII , 1158; XII , 757; XIX , 368–369; J. C. Poggendorff, Biographisch-Literarisches Handwörterbuch, III , 1393; IV , 1570-1571.

Violle summarized his work in the autobiographical essay Notice sur les travaux scientifiques de M. Jules Violle (Paris, 1889).

II. Secondary Literature. P. Villard’s obituary address is in Comptes rendus hebdomadaires des séances de l’Académie des sciences, 177 (1923), 513–515. Samuel P. Langley discussed Violle’s work on the solar constant (and other earlier work) thoroughly in his Researches on Solar Heat and Its Absorption by the Earth’s Atmosphere (Washington, D. C., 1884).

Sigalia Dostrovsky