By Daniel Simkin, IET Research Librarian

The image above is of the moon observed by Galileo and included in the second edition of the rare book Institutio Astronomica by Pierre Gassendi, published in 1647. The edition held by the IET was printed in London in 1653 by Jacobi Flesher and forms part of the collection of Silvanus P. Thompson purchased in 1917 by the IET. Significantly this edition also includes Galileo’s Sidereus nuncius and Johannes Kepler’s Dioptrice, two important works of telescopic astronomy, and is the first publication in England of all three works.

Institutio Astronomica is based on a series of lectures that Gassendi gave when he was a lecturer in mathematics and is regarded as one of the first modern astronomy textbooks. It is divided into three parts, the first discussing the theory of the spheres, the second describing astronomical theory, and the third examining the conflicting ideas of Tycho Brahe and Nicolaus Copernicus. Gassendi wrote biographies of Brahe and Copernicus as well as other philosophers and scientists.

Who was Pierre Gassendi?

Pierre Gassendi was born in 1592 in Champtercier in Southern France. He was recognised at an early age for his academic achievements and studied philosophy at the University of Aix-en-Provence before gaining his doctorate in theology at the University of Avignon in 1614. In 1617 he was appointed to the position of chair of philosophy at the University of Aix-en-Provence. He left the university when in 1623 The Jesuit Order assumed control of the university and required all academics to be Jesuits. Gassendi then travelled in France and further afield in Belgium and the Netherlands, continuing to teach and write. In 1645 he was appointed to the chair of mathematics at College Royal in Paris and divided his time between Paris and Digne-Les-Bains in Southern France where he was provost of the cathedral. In 1648 he gave up his position in Paris owing to ill health and spent time travelling in the south of France. In 1653 he returned to Paris to write, but the lung disease with which he suffered worsened and he died in Paris in 1655.

As well as working in the Catholic priesthood and teaching and writing on philosophy, Gassendi was an astronomer and mathematician credited with several scientific achievements. He was an empiricist, believing that experimentation and observation were vital scientific methods to test hypotheses and theories. He is best known as an observational scientist for being the first person to record the transit of Mercury across the sun in 1631. Other achievements include using a camera obscura to gauge the diameter of the moon and measuring the speed of sound. He has been honoured by a bronze statue erected in 1852 in Digne-Les-Bains and the lunar crater Gassendi is named after him.

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