Jean-Jacques d'Ortous de Mairan

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Jean-Jacques d'Ortous de Mairan (November 26, 1678 – February 20, 1771) was a French geophysicist.

He was born in the town of Béziers. His father, François d'Ortous, belonged to the landed gentry, but he died when Jean-Jacques was four. His mother would die when Jean-Jacques was sixteen in 1694.

He attended college in Toulouse, with a focus in ancient Greek. In 1698 he went to Paris to study mathematics and physics.

In 1718 he was made a member of the Académie Royal des Sciences, and held offices at various times up until 1760, including the positions of secretary, assistant director, and director. Eventually he was appointed editor of the Journal des Savans, a science periodical.

In 1729 he devised an experiment showing the existence of a circadian rhythm in plants, presumably originating from an endogenous clock . See the shows in an interactive museum.

In 1731 he observed a nebulosity around a star near the Orion nebula. This was later designated M43.

He died of pneumonia in Paris.