René Just Haüy

René Just Haüy () FRS MWS FRSE (28 February 1743 – 1 June 1822) was a French priest and mineralogist, commonly styled the Abbé Haüy after he was made an honorary canon of Notre Dame. Due to his innovative work on crystal structure and his four-volume ''Traité de Minéralogie'' (1801),
he is often referred to as the "Father of Modern Crystallography". During the French revolution he also helped to establish the metric system.

Biography

Early life

René-Just Haüy was born at Saint-Just-en-Chaussée on February 28, 1743, in the province of Île-de-France (later the ''département'' of Oise). His parents were Just Haüy, a poor linen-weaver, and his wife Magdeleine Candelot.

Haüy's interest in the services and music of the local church brought him to the attention of the prior of a nearby abbey of Premonstrants. Through him, Haüy was introduced to a colleague in Paris and obtained a scholarship to the College of Navarre. Haüy eventually became an usher, and in 1764, was appointed regent (master) of the fourth class.

Haüy also progressed in his religious training. He was tonsured in 1762, took minor orders in 1765, was appointed a subdeacon in 1767, became a deacon in 1769, and was ordained as a Roman Catholic priest in 1770.

After his ordination, Haüy became regent (teacher) of the second class at the Collège du Cardinal-Lemoine.
Through his friendship with his spiritual director, Abbé Lhomond, Haüy became interested first in botany, and after hearing a lecture by Louis-Jean-Marie Daubenton, in mineralogy.

His brother Valentin Haüy was the founder of the first school for the blind, the Institution des Jeunes Aveugles (Institute for Blind Youth) in Paris.

Crystallography

An accident apparently directed René-Just Haüy's attention to what became a new field in natural history, crystallography. Haüy was examining a broken specimen of calcareous spar in the collection of Jacques de France de Croisset. (According to some accounts, Haüy dropped the specimen and caused it to break.) He became intrigued by the perfectly smooth plane of the fracture.

Studying the fragments inspired Haüy to make further experiments in crystal cutting. Breaking down crystals to the smallest pieces possible, Haüy concluded that each type of crystal has a fundamental primitive, nucleus or “integrant molecule” of a particular shape, that could not be broken further without destroying both the physical and chemical nature of the crystal. He further argued that crystal structures are made up of orderly arrangements of these integrant molecules in successive layers, according to geometrical laws of crystallization.
Crystals that had been classed together previously were identified as being of separate mineral species if their fundamental structure differed. Heavyspar, for example, was differentiated into specimens containing barium and strontium.
The value of Haüy's discovery was immediately recognized.

Haüy and his contemporaries worked with limited evidence. They could observe a crystal's habit and cleavage planes and measure interfacial angles with an instrument called a goniometer. The internal structure underlying the crystal's integrant molecule would not be determinable until the development of X-Ray diffraction technology many years later, in 1902.
Haüy was not the only researcher to observe that calcite crystals could be composed of smaller rhombohedra, but it was he who introduced the idea of triple periodicity in crystals.

This idea was fundamental to later developments in the field on crystal lattices.

Between 1784 and 1822, Haüy published more than 100 reports discussing his theories and their application to the structure of crystalline substances.
Haüy first stated his laws of decrement in ''Essai d'une théorie sur la structure des crystaux'' (1784). It was a radical departure from his previous works, introducing his theory of ''molé constituantes'' or constituent molecules.
By 1792, he had identified a number of parallelepipeds as possible primitive crystal forms.
Haüy worked out the mathematical theory of his work in his ''Traité de minéralogie'' (1801), which became a classic in the field. By then, Haüy had applied his ideas to the differentiation of different species. He systematically described all the known minerals, sorting them into classes, and giving their chemical and geometrical properties. His work, in four volumes, including an atlas of plates, was accounted among the most wonderful of the 19th century. It has been described as "a work of comprehensive insight, and much of it, written with literary fluency". A second updated edition appeared as ''Traité de cristallographie'' in 1822.

Haüy created comprehensive collections containing hundreds of pear-wood models of crystal models for education and demonstrations. One such set was acquired by Martin van Marum, curator of the Teylers Museum and a director of the Hollandsche Maatschappij der Wetenschappen.

Haüy is also known for his observations on pyroelectricity. He detected pyroelectricity in calamine, an oxide of zinc, as early as 1785.
He studied pyroelectricity in a number of other minerals including tourmaline and related them to crystalline structure.
He showed that electricity in tourmaline was strongest at the poles of the crystal and became imperceptible at the middle.
Haüy published a book on electricity and magnetism, ''Exposition raisonné de la théorie de l'électricité et du magnétisme, d'après les principes d'Æpinus'', in 1787.

On February 12, 1783, Haüy was elected to the Académie royale des sciences de Paris (French Academy of Sciences) with the rank of an adjoint in botany, there being no vacancy in either physics or mineralogy. In 1788, he became as an associate in natural history and mineralogy.

French Revolution

During the French Revolution, Haüy refused to take an oath accepting the Civil Constitution of the Clergy, and became a non-juring priest. He was thrown into prison after the monarchy was overthrown on August 10, 1792. Étienne Geoffroy Saint-Hilaire interceded on his behalf. Haüy was released just a few days before the September Massacres of September 2–7, 1792 in which many of the clergy were killed.

On August 8, 1793, in spite of the efforts of Antoine Lavoisier

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