View source for Jean-André Deluc

{{Short description|Swiss geologist and meteorologist (1727–1817)}}
{{redirect|Deluc|the crater|Deluc (crater)}}
{{EngvarB|date=July 2017}}
{{Use dmy dates|date=July 2017}}
{{Infobox scientist
|name              = Jean-André Deluc
|image             = Jean-André Deluc.jpg
|image_size       = 
|caption           = 
|birth_date        = {{birth date|df=yes|1727|2|8}}
|birth_place       = [[Geneva]], [[Republic of Geneva]]
|death_date        = {{death date and age|df=yes|1817|11|7|1727|2|8}}
|death_place       = [[Windsor, Berkshire]], England
|residence         = 
|citizenship       = 
|nationality       = Genevan, then Swiss since 1815
|field             = Geology, [[meteorology]]
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|known_for         = 
|author_abbrev_bot = 
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}}
'''Jean-André Deluc''' or '''de Luc'''<ref name=spelling/> (8 February 1727 – 7 November 1817) was a geologist, natural philosopher and [[meteorologist]] from the [[Republic of Geneva]]. He also devised [[measuring instrument]]s.

== Biography ==
Jean-André Deluc was born in [[Geneva]]. His family had come to the [[Republic of Geneva]] from [[Lucca]], Italy, in the 15th century.<ref name=lucques/> His mother was Françoise Huaut. His father, Jacques-François Deluc,<ref name=Sigrist/> had written in refutation of [[Bernard Mandeville]] and other rationalistic writers, but he was also a decided supporter of Jean-Jacques Rousseau.<ref name=letterByRousseau/>

As a student of [[Georges-Louis Le Sage]], Jean-André Deluc received a basic education in mathematics and in natural philosophy. He engaged early in business, which occupied a large part of his first adult years, with the exception of scientific investigation in the Alps. With the help of his brother Guillaume-Antoine, he built a splendid collection of [[mineralogy]] and [[fossils]].<ref>René Sigrist, "Collecting nature's medals", in John Heilbron & René Sigrist (eds), ''Jean-André Deluc. Historian of Earth and Man'', Geneva, Slatkine, 2011, p. 105-146.</ref><ref name=museum/>

Deluc also took part in politics. In 1768, sent on an embassy to the [[Étienne François, duc de Choiseul|duc de Choiseul]] in Paris, he succeeded in gaining the duke's friendship. In 1770 he became a member of the [[Council of Two Hundred]] in Geneva.

Three years later, business reverses forced him to leave his native town; he returned, briefly, only once. The change freed him for non-scientific pursuits; with little regret he moved to Great Britain in 1773, where he was appointed reader to [[Charlotte of Mecklenburg-Strelitz|Queen Charlotte]], a position he held for forty-four years and that afforded him both leisure and income.{{sfn|Chisholm|1911|pp=975–976}}

Despite his duties at court, he was given leave to make several tours of Switzerland, France, Holland and Germany. At the beginning of his German tour (1798–1804), he was distinguished with an honorary professorship of philosophy and geology at the [[University of Göttingen]], which helped to cover diplomatic missions for the king George III. Back to Britain, he undertook a geological tour of the country (1804–1807).<ref name=Michaud/>{{sfn|Chisholm|1911|p=976}}

In 1773 Deluc was made a [[fellow of the Royal Society]]; he was a correspondent of the [[French Academy of Sciences]] and a member of several other [[learned society|learned societies]]. He died at [[Windsor, Berkshire]], England, in 1817, after nearly 70 years of research. [[Deluc (crater)|Deluc]], an [[impact crater]] on the Moon, was given his name.

== Scientific contributions ==

=== Observations and theory ===
Deluc's main interests were geology and meteorology; [[Georges Cuvier]] mentions him as an authority on the former subject.<ref name=Cuvier/> His major geological work, ''Lettres physiques et morales sur les montagnes et sur l'histoire de la terre et de l'homme'' (6 vol., 1778–1780), was dedicated to Queen Charlotte. He published volumes on geological travels: in northern Europe (1810), in England (1811), and in France, Switzerland and Germany (1813).{{sfn|Chisholm|1911|p=976}}

Deluc noticed the disappearance of heat in the thawing of ice about the same time that [[Joseph Black]] made it the foundation of his hypothesis of [[latent heat]]. He ascertained that water was densest at about 5&nbsp;°C (and not at the freezing temperature).<ref name=Recherches/> He was the originator of the theory, later reactivated by [[John Dalton]], that the quantity of [[water vapour]] contained in any space is independent of the presence or density of the air, or of any other elastic fluid.{{sfn|Chisholm|1911|p=976}}

His book ''Lettres sur l'histoire physique de la terre'' (Paris, 1798), addressed to [[Johann Friedrich Blumenbach]], develops a theory of the Earth divided into six periods modelled on the six days of Creation. It contains an essay on the existence of a [[Moral realism|General Principle of Morality]] and gives an interesting account of conversations with [[Voltaire]] and [[Rousseau]]. Deluc was an ardent admirer of [[Francis Bacon]], on whose writings he published two works: ''Bacon tel qu'il est'' (Berlin, 1800), showing the bad faith of the French translator, who had omitted many passages favorable to revealed religion, and ''Précis de la philosophie de Bacon'' (2 vols 8vo, Paris, 1802), giving an interesting view of the progress of natural science. ''Lettres sur le christianisme'' (Berlin and Hanover, 1803) was a controversial correspondence with [[Wilhelm Abraham Teller]] of Berlin in regard to the [[Moses|Mosaic]] [[cosmogony]]. His ''Traité élémentaire de géologie'' (Paris, 1809, translated into English by Henry de la Fite the same year) was principally intended as a refutation of [[James Hutton]] and [[John Playfair]]. They had shown that geology was driven by the operation of internal heat and erosion, but their system required much more time than Deluc's [[Moses|Mosaic]] variety of [[neptunism]] allowed.{{sfn|Chisholm|1911|p=976}}

Many other papers were in the ''Journal de Physique'', in the ''Philosophical Transactions'' and in the ''[[Philosophical Magazine]]''.{{sfn|Chisholm|1911|p=976}}

=== Instruments ===
[[File:Whalebone hygrometer-MHS 1085-P4070321-gradient.jpg|thumb|Deluc's whalebone hygrometer, on display at the [[Musée d'histoire des sciences de la ville de Genève]].|left]]
[[File:Deluc-4.jpg|thumb|237x237px|Introduction page of a 1772 copy of volumes 1 of "''Recherches sur les modifications de l'atmosphère''"]]
Deluc dedicated a large part of his activity to perfecting or inventing [[measuring instrument]]s.

He devised a portable barometer for use in geological expeditions.<ref name=barometer/> His ''Recherches sur les modifications de l'atmosphère'' (2 vols. 4to, Geneva, 1772; 2nd&nbsp;ed., 4&nbsp;vols. Paris, 1784) contain experiments on moisture, evaporation and the indications of [[hygrometer]]s and [[thermometer]]s. He applied the [[barometer]] to the determination of heights. The ''[[Philosophical Transactions]]'' published his account of a new hygrometer, which resembled a mercurial thermometer, with an ivory bulb, which expanded by moisture, and caused the mercury to descend.<ref name=hygrometer/> He later devised a whalebone hygrometer which sparked a bitter controversy with [[Horace-Bénédict de Saussure]], himself inventor of a hair hygrometer.<ref>René Sigrist, "Scientific standards in the 1780s: A controversy over hygrometers", in John Heilbron & René Sigrist (eds), ''Jean-André Deluc. Historian of Earth and Man'', Geneva, Slatkine, 2011, p. 147-183.</ref> He gave the first correct rules for measuring heights with the help of a barometer<!-- Please beware of the mention in 1911 Britannica: "in the ''Philosophical Transactions'', 1771, p. 158"-->.<ref name=AltitudeBarometer/>

Based on his experiments in 1772, Deluc advocated the use of [[Mercury (element)|mercury]], instead of alcohol or other fluids, in thermometers, as its volume varies the most linearly with the method of mixtures. In detail, if two portions of water of equal masses A, B were mixed, and let the resulting water be C, and if we immerse a thermometer in A, B, C, we obtain lengths <math>l_A, l_B, l_C</math>. Deluc expected that <math>l_C = \frac 12 (l_A + l_B)</math>, and similarly for other ratios of mixtures. He found that thermometers made using mercury allowed the closest fit to his expectation of linearity.<ref>{{Cite book |last=Chang |first=Hasok |url=https://www.worldcat.org/oclc/457147642 |title=Inventing temperature : measurement and scientific progress |date=2007|page=64 |isbn=978-0-19-533738-9 |location=Oxford |oclc=457147642}}</ref>

In 1809 he sent a long paper to the Royal Society on separating the chemical from the electrical effect of the [[dry pile]], a form of [[Voltaic pile]],<ref name=Nicholson/> with a description of the electric column and aerial electroscope, in which he advanced opinions contradicting the latest discoveries of the day; they were deemed inappropriate to admit into the ''Transactions''.{{sfn|Chisholm|1911|p=976}} The dry column described by Deluc was constructed by various scientists and his improvement of the dry pile has been regarded as his most important work, although he was not in fact its inventor. He was a valued mentor to the young [[Francis Ronalds]], who published several papers on dry piles in 1814–15.<ref>{{Cite book|title=Sir Francis Ronalds: Father of the Electric Telegraph|last=Ronalds|first=B.F.|publisher=Imperial College Press|year=2016|isbn=978-1-78326-917-4|location=London}}</ref><ref>{{Cite journal|last=Ronalds|first=B.F.|date=July 2016|title=Francis Ronalds (1788–1873): The First Electrical Engineer?|journal=Proceedings of the IEEE|volume=104|issue=7|pages=1489–1498|doi=10.1109/JPROC.2016.2571358|s2cid=20662894}}</ref><gallery>
File:Deluc-1.jpg|1772 copy of volumes 1 and 2 of "''Recherches sur les modifications de l'atmosphère''"
File:Deluc-2.jpg|Title page of a 1772 copy of volume 1 of "''Recherches sur les modifications de l'atmosphère''"
File:Deluc-3.jpg|Table of contents page of a 1772 copy of volume 1 of "''Recherches sur les modifications de l'atmosphère''"
File:Deluc-7.jpg|Dedication to a 1772 copy of volume 1 of "''Recherches sur les modifications de l'atmosphère''"
File:Deluc-8.jpg|Dedication to a 1772 copy of volume 1 of "''Recherches sur les modifications de l'atmosphère''"
File:Deluc-5.jpg|First page of a 1772 copy of volume 1 of "''Recherches sur les modifications de l'atmosphère''" 
</gallery>

===Scriptural and observational data===
The last decades of Deluc's life were occupied with theological considerations.<ref name=Sigrist/> In his controversy with Hutton, "while never arguing that Hutton was an atheist, Deluc did accuse him of failing to counter [[atheism]] sufficiently".<ref name=Dean/>

He took care in reconciling observational data and the Scriptures considered as a description of the history of the world. In his ''Lettres physiques et morales'' he explained the six days of the creation as epochs preceding the current state of the globe, and attributed the deluge to the filling up of cavities in the interior of the earth.{{sfn|Chisholm|1911|p=976}}

The subject is discussed at length by Martina Kölbl-Ebert in ''Geology and Religion''.<ref name=GeolReligion/>

==See also==
*[[History of geology#18th century]]
*[[Plutonism]]

==Bibliography==

===Selection===
* "Account of a new hygrometer", ''Philosophical Transactions'', 63/2, 1773, p.&nbsp;404–460.
* "Barometrical observations on the depth of the mines in the Hartz", ''Philosophical Transactions'', 67/2, 1777, p.&nbsp;401–550.
* ''An essay on pyrometry and areometry and on physical measures in general'', London, Nichols, 1778–79 (2 vols).
*{{google books|Cw4AAAAAQAAJ|page=PR1|An elementary treatise on geology}} (1809); translated by Henry De La Fite (d. 1831).
*''Geological travels'', London, 1810–11 (3 vols): ''Travels in the north of Europe'' (vol. 1); ''Travels in England'' (vols 2 & 3).
*''Experiments concerning the electric machine: showing the electric effects of frictions between bodies'', London, 1811.
*''Geological travels in some parts of France, Switzerland, and Germany'': vol. 1 (1813) (nos. 1–453), vol. 2 (1813) (nos. 454–844), vol. 3 (1811) (nos. 935–1417) on [[Google Books]]<ref>There is some confusion in the numbering of volumes by Google Books (August 2013).</ref>
*''Letters on the physical theory of the earth, addressed to Professor Blumenbach'', London, 1831 (With introductory remarks and illustrations by Henry De La Fite).

===Lists of online works===
*[http://www.e-rara.ch/search/quick?max=20&query=Jean+Andr%C3%A9+Deluc List] of online works on [[e-rara.ch]]. {{in lang|fr|de}}
*[http://rstl.royalsocietypublishing.org/search?submit=yes&submit=Submit&author1=Deluc&hits=10&sortspec=relevance&submit=yes Articles] published in the [[Philosophical Transactions of the Royal Society]]. {{in lang|fr}}
* Jean-André Deluc (1779–1780) ''Lettres physiques et morales sur l'histoire de la terre et de l'homme, 5 vol.'' – digital facsimile from the [[Linda Hall Library]]
* Jean-André Deluc (1810–1811) ''Geological Travels. 3 vol.'' (English) – digital facsimile from the [[Linda Hall Library]]

==References==
{{Reflist
 |refs=
<ref name=AltitudeBarometer>Deluc published a two-part article on the subject in the ''Phil. Trans.'': "Barometrical observations on the depth of the mines in the Hartz". [http://rstl.royalsocietypublishing.org/content/67/401.full.pdf+html?sid=ee9a5f98-a247-4645-86a7-80f5c679bd0b Part 1] ({{doi|10.1098/rstl.1777.0023}}); [http://rstl.royalsocietypublishing.org/content/69/485.full.pdf+html?sid=ee9a5f98-a247-4645-86a7-80f5c679bd0b Part 2] ({{doi|10.1098/rstl.1779.0032}})</ref>
<ref name=barometer>Especially [https://books.google.com/books?id=eDcVAAAAQAAJ&pg=PA214 "Remarques sur les baromètres destinés au transport"]. ''Recherches sur les modifications de l'atmosphère'', vol.&nbsp;1, p.&nbsp;214</ref>
<ref name=Cuvier>No less than ten times in his [https://books.google.com/books?id=HTOGyJJl26YC&q=Deluc ''Rapport historique sur les progrès des sciences naturelles...'']</ref>
<ref name=Dean>Dean, Dennis R. [https://archive.org/details/jameshuttonhisto00dean/page/81 ''James Hutton and the history of geology'', p.&nbsp;81]</ref>
<ref name=GeolReligion>See for example the [https://books.google.com/books?id=w1NUHmio_jEC&pg=PR15 passage starting on page 9], "Views of J.-A. Deluc's geological ideas", of Martina Kölbl-Ebert book's ''Geology and religion: a history of harmony and hostility''. Geological Society, 2009 {{ISBN|1862392692}}, {{ISBN|9781862392694}}</ref>
<ref name=hygrometer>[http://rstl.royalsocietypublishing.org/content/63/404.full.pdf+html?sid=ee9a5f98-a247-4645-86a7-80f5c679bd0b "Account of a new hygrometer"] (1773); [http://rstl.royalsocietypublishing.org/content/81/389.full.pdf+html?sid=ee9a5f98-a247-4645-86a7-80f5c679bd0b "A second paper on hygrometry"] (1791)</ref>
<ref name=letterByRousseau>[[Jean-Jacques Rousseau]], while a friend of his father's, considered the personage and his writings as boring: [https://books.google.com/books?id=uUs6AAAAcAAJ&pg=PA383 ''Histoire de la vie et des ouvrages de J.-J. Rousseau'', vol.&nbsp;1, p.&nbsp;383]. See also Miller, James. [https://books.google.com/books?id=96HrRaki4akC&pg=PA51 ''Rousseau: dreamer of democracy'', Hackett Publishing, 1984, p.&nbsp;51]</ref>
<ref name=lucques>"Deluc" = "De Luc" = "De Lucques" (same pronunciation); "Lucques" is the French name of the city of Lucca.</ref>
<ref name=Michaud>[[#Michaud|Michaud]]</ref>
<ref name=museum>The collection later came into the hands of his nephew, also named Jean-André (1763–1847) and a writer on geology as well, who enlarged it. It is now at the [[Natural History Museum of Geneva]].</ref>
<ref name=Nicholson>''Nicholson's Journal'', 1810</ref>
<ref name=Recherches>La Température où l'eau est le plus condensée, est à peu près à 4 °Ré (5 °C) [https://books.google.com/books?id=JNWIH3-QEIoC&dq=%22plus+condens%C3%A9e%2C+est+%C3%A0-peu-pr%C3%A8s+%C3%A0%22&pg=PA274 page 274]</ref>

<ref name=Sigrist>Sigrist</ref>
<ref name=spelling>Always generally spelled "Deluc". In 1820, [[#Michaud|Michaud]]'s article about Jean-André De Luc is under "Luc", while the article about his brother Guillaume-Antoine is under "Deluc".</ref>

}}

==Sources==
* {{EB1911|wstitle=Deluc, Jean André|volume=7|pages=975–976}}
* Harrison, William Jerome. {{cite DNB|wstitle=Deluc, Jean André}}
* Heilbron, John L.; Sigrist, René (ed.). ''Jean-André Deluc, historian of earth and man''. Geneva: Slatkine 2011.
* {{Anchor|Michaud}}[[Joseph François Michaud|Michaud, Joseph-François]]; Michaud, Louis Gabriel. "Luc (Jean-André de)". ''Biographie universelle, ancienne et moderne'', vol.&nbsp;25. 1820
* Sigrist, René. ''[https://hls-dhs-dss.ch/fr/articles/015896/2003-12-12/ Jean-André Deluc]''. ''[[Historical Dictionary of Switzerland]]'' {{in lang|fr}}. Also available in German and Italian.

== External links ==

* Jean-Andre DeLuc papers (MS 179). Manuscripts and Archives, Yale University Library.[http://hdl.handle.net/10079/fa/mssa.ms.0179]

<br />{{Copley Medallists 1751-1800}}

{{Authority control}}

{{DEFAULTSORT:Deluc, Jean-Andre}}
[[Category:1727 births]]
[[Category:1817 deaths]]
[[Category:18th-century scientists from the Republic of Geneva]]
[[Category:18th-century politicians from the Republic of Geneva]]
[[Category:Philosophers from the Republic of Geneva]]
[[Category:Mountain climbers from the Republic of Geneva]]
[[Category:Fellows of the Royal Society]]
[[Category:Members of the French Academy of Sciences]]
[[Category:Recipients of the Copley Medal]]
[[Category:19th-century Swiss geologists]]
[[Category:Meteorologists from the Republic of Geneva]]
[[Category:Swiss meteorologists]]