Jules Louis Gabriel Violle (16 November 1841 – 12 September 1923) was a French

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...

and

inventor An invention is a unique or novel device, method, composition, idea or process. An invention may be an improvement upon a machine, product, or process for increasing efficiency or lowering cost. It may also be an entirely new concept. If an ...

. He is notable for having determined the

solar constant The solar constant (''GSC'') is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit area. It is measured on a surface perpendicular to the rays, one astronomical unit (au) from the Sun (roughly the ...

Mont Blanc Mont Blanc (french: Mont Blanc ; it, Monte Bianco , both meaning "white mountain") is the highest mountain in the Alps and Western Europe, rising above sea level. It is the second-most prominent mountain in Europe, after Mount Elbrus, and i ...

in 1875, and, in 1881, for proposing a standard for

luminous intensity In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. ...

, called the Violle, equal to the light emitted by 1 cm² of

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...

at its

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

. It was notable as the first unit of light intensity that did not depend on the properties of a particular lamp. This was much larger than traditional measures such as candlepower, so the standard SI unit

candela The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to ...

was originally defined in 1946 as 1/60 Violle. Throughout his life, Violle taught at several colleges including the

University of Lyon The University of Lyon (french: Université de Lyon), located in Lyon and Saint-Étienne, France, is a center for higher education and research comprising 11 members and 24 associated institutions. The three main universities in this center are: ...

and the

Conservatoire des Arts et Métiers A music school is an educational institution specialized in the study, training, and research of music. Such an institution can also be known as a school of music, music academy, music faculty, college of music, music department (of a larger ins ...

Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...

. He was one of the founders of the

Institut d'optique théorique et appliquée The Institut d'optique Graduate School ("Institute of optics"), nicknamed SupOptique or IOGS, is one of the most prestigious French Grandes Ecoles and the leading French ''grande école'' in the field of Optics and its industrial and scientific ap ...

and the

École supérieure d'optique The Institut d'optique Graduate School ("Institute of optics"), nicknamed SupOptique or IOGS, is one of the most prestigious French Grandes Ecoles and the leading French ''grande école'' in the field of Optics and its industrial and scientific ap ...

. He improved and invented a number of devices for measuring radiation, and determined the

freezing Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...

and

s of

palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...

. Violle is believed by some to be the secret identity of

Fulcanelli Fulcanelli (fl. 1920s) was the name used by a French alchemist and esoteric author, whose identity is still debated. The name Fulcanelli seems to be a play on words: Vulcan, the ancient Roman god of fire, plus El, a Canaanite name for God and so ...

, a contemporary French alchemist whose true identity is still debated. His biography can be found in this book: ''"A l'ombre des chênes, l'alchimiste de la République"''

External links

* {{DEFAULTSORT:Violle, Jules Louis Gabriel 1841 births 1923 deaths People from Langres French physicists École Normale Supérieure alumni Members of the French Academy of Sciences Commandeurs of the Légion d'honneur