Jean-André Deluc or de Luc[1] (8 February 1727 – 7 November 1817) was a geologist, natural philosopher and meteorologist from the Republic of Geneva.

His father, Jacques-François Deluc,[3] had written in refutation of Bernard Mandeville and other rationalistic writers, but he was also a decided supporter of Jean-Jacques Rousseau.

[4] 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.

The change freed him for non-scientific pursuits; with little regret he moved to Great Britain in 1773, where he was appointed reader to Queen Charlotte, a position he held for forty-four years and that afforded him both leisure and income.

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.

He published volumes on geological travels: in northern Europe (1810), in England (1811), and in France, Switzerland and Germany (1813).

[11] 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.

[9] 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 General Principle of Morality and gives an interesting account of conversations with Voltaire and Rousseau.

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 Mosaic variety of neptunism allowed.

[15] Based on his experiments in 1772, Deluc advocated the use of mercury, instead of alcohol or other fluids, in thermometers, as its volume varies the most linearly with the method of mixtures.

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,[17] 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.

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.