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Jean Tarde

Jean Tarde was a Frenchman and was an early adopter of Copernican theory. He was born into a semi wealthy family in the bourgeois community in La Roque-Gajac, near Sarlat, France. He received his doctorate of law from the University of Cahors and then went on to the University of Paris to continue his studies. Throughout his younger adult life, he maintained many different religious positions such as canon theologian, and almoner where during his free time he studied various sciences including mathematics, astronomy, physics, and geography. He is most famous for his work with sunspots which he concluded were small satellites of the sun.

Early Life

Jean Tarde was born in 1561 into the family of Sarlat which dated back to the 14^th century. His family consisted of two different branches including the du Ponts, and the de Lisles. Tarde belonged to the du Pont branch. Not much is known about his family except that they were likely a member of the bourgeois in 16^th century France. His father, although his name is unknown, is known to have been a Gentry.

Religious Work

After finishing his education he was ordained and became a priest of the parish of Carves which is near Belves. He was promoted to canon theologian of Sarlat’s cathedral which opened up many different opportunities for him within the Catholic church. Between the years of 1562 and 1598, there were a series of wars in France involving the Roman Catholics and the Huguenots (French Protestants). One of the consequences of these wars was the destruction of the Cathedral’s archives. Tarde was put in charge of reconstituting these archives. During the final years of these wars, the Bishop of Tarde’s church in Sarlat, Louis de Salignac, was interested in finding out the effects of these wars on the surrounding community. He appointed Tarde as the vicar General in 1594 and commissioned him to map out the area under the churches jurisdiction. Henry IV of France appointed him his almoner (royal chaplain) in 1599 which became Tarde’s main source of income.

Cartography

A photo of a quadrant. The type of instrument Tarde used for his calculations.

As promised, Tarde mapped out the surrounding area of the church for the Bishop in 1606. He used a quadrant with a compass needle attached to a sundial. This tool allowed him to calculate distances and various angles. He published his works in 1621 titled Les usages du quadrant à l'esguille aymantée which was dedicated to the bishop.

Early Scientific Work

His work in cartography demonstrated his proficiency in various subjects such as geometry, drawing, and the use of various instruments in the sciences. Tarde traveled often and in November of 1614, he made a journey to Italy. During this journey, he stopped in Florence to meet the famous astronomer Galileo Galilei. Due to his interest in astronomy, Tarde spoke with Galileo about his book Siderius nuncius, which encompassed Galileo’s first discoveries made through a telescope. They spoke of various observations made by Galileo including the rings of Saturn (at the time believed to be two stars), the phases of Venus, and some unknown spots on the face of the sun. Galileo informed Tarde that these spots were not illusions and were seen by others outside of Galileo’s observations and that they took around two weeks to cross the face of the sun. Tarde took quickly to the idea of the telescope and asked Galileo for help on building one. He promised to send Tarde a lens, but Tarde never received one.

Astronomical Work

After returning to France, Tarde built his own personal observatory in order to study the sunspots him and Galileo discussed. There he published works such as Borbonia sidera, (1620) which were his findings based on his conversations with Galileo, and Telescopium, seu demonstrations opticae, (1622) which was his book defending the validity of data gathered from a telescope as well as described how the caverne obscure, a telescope that projected an image of the Sun on a white surface in a dark room, worked and aided his studies of sun spots.

After studying sunspots for over five years, Tarde came to the conclusion that they were not actually spots on the sun, but that they were planets that that orbited the sun. He named these planets the Bourbon stars, commemorating them to the French royal family. Part of the reason he reached this conclusion was that Tarde was a believer that the Sun was a perfect surface and had no blemishes or imperfections on its surface. Tarde was determined to fit Aristotelian theory into his hypothesis as well as heliocentric theory. He cited Pythagorean as well as Copernican theory in his findings as well. Due to the church’s ban on Copernicanism, Tarde did not fully commit himself to heliocentrism but instead argued in favor of it for the sake of calculations.

This conclusion sparked a heated debate between him and Galileo. Galileo mentioned several objections to Tarde’s theory including the fact that the sunspots did not exhibit retrograde motion as all other planets did. Tarde’s argument was that weather interfered with his observations and that tracking retrograde motion was too difficult for these planets because of how close to the sun they were.

Death

Jean Tarde died in 1636 in Sarlat, France. He was 75 years old.