Born on 26 November 1678 in Béziers, France, Jean-Jacques de Mairan was a geophysicist, astronomer, and chronobiologist. After studying ancient Greek in Toulouse from 1694 to 1697, de Mairan went to Paris in 1698 to study physics and mathematics under Nicolas Malebranche. In 1702 de Mairan returned to Béziers, where he continued his scientific studies. In 1718 he went to Paris and became an associate member of the Royal Academy of Sciences, for which he served as secretary from 1741 to 1743. In 1735 he was elected a fellow of the Royal Society and would go on to enjoy membership in the Royal Societies of London, Edinburgh, and Uppsala. Over his lifetime, de Mairan would study a variety of subjects, including heat, light, sound, Earth’s shape, and the rotation of the Moon. De Mairan was the first to describe what is now known as circadian rhythm when he observed the opening and closing of the leaves of the mimosa plant, even when it was confined to a dark room. Another of his experiments centered on the varying obliquity of sunlight across the seasons. De Mairan died of pneumonia at age 92 in 1771. (Image credit: Wellcome Library no. 6129i, CC BY 4.0)
