(b. La Roque-Gageac, France, 1561 or 1562; d. Sarlat, France, 1636)
After receiving a doctorate in law from the University of Cahors, Tarde continued his studies at the Sorbonne. Ordained a priest, he was assigned to the parish of Carves, near Belvès, and later rose to be the canon theologian of the cathedral church of Sarlat. In 1594, when the bishop wished to determine the effects of the religious wars in France on the diocese of Sarlat, he designated Tarde vicar-general and commissioned him to make a map of the bishopric.
Tarde charted the neighboring diocese for the bishop of Cahors in 1606. In this topographical survey he used a small quadrant equipped with a compass needle and attached to a sundial. In compliance with the bishop’s request that he publish an explanation of this instrument. Tarde wrote and dedicated to the bishop Les usages du quadrant à l’esguille aymantée (1621), for which the royal privilege was dated 8 June 1620. On the same day Tarde obtained privileges for the two other works published during his lifetime: Borbonia sidera (1620) and his translation of this Latin treatise into French, Les astres de Borbon (1622). These works were based on Tarde’s conversations with Galileo, whom he had visited in Florence on 12 – 15 November 1614. Among the numerous subjects they discussed were the recently discovered sunspots. After returning to France. Tarde observed the spots for five years and reached the erroneous conclusion that they were planets, which he proceeded to name in honor of the French royal house, as Galileo had done with the satellites of Jupiter and the Medici family.
Tarde’s interpretation of the sunspots was demolished by Gassendi in a letter to Galileo dated 20 July 1625. In that communication he pointed out that despite an assiduous program of observations, Tarde had been unable to identify any sunspot that exhibited the periodic returns characteristic of the true planets, as Tarde himself acknowledged.
I. Original Works. Tarde’s published works are Borbonia sidera (Paris, 1620), translated by Tarde as Les astres de Borbon (Paris, 1622, 1623, 1627); Les usages du quadrant à l’esguille aymantée (Paris, 1621, 1623, 1627, 1638); and Les chroniques de Jean Tarde, Gaston de Gérard and Gabriel Tarde, eds. (Paris, 1887). Unpublished is “Voyage de Jean Tarde dans le midi et en Italie,” listed by Philippe Lauer in Bibliothèque Nationale (Paris), Collections manuscrites sur l’histoire des provinces de France, inventaire, II (Paris, 1911), p. 60, no. 106, fols. 26 – 38. For the various eds. of his map of the bishopric of Sarlat, see pp. 395 – 396 in Dujarric-Descombes, who enumerated Tarde’s other geographical works.
II. Secondary Literature. See Albert Dujarric-Descombes, “Recherches sur les historiens du Périgord au XVIIe siècle,” in Bulletin de la Société historique et archéologique du Périgord, 9 (1882), 371 – 412, 489 – 497; Antonio Favaro, “Di Giovanni Tarde e di una sua visita a Galileo dal 12 al 15 novembre 1614,” in Bullettino di bibliografia e storia delle scienze matematiche e fisiche, 20 (1887), 345–371, 374: “Lettre de Claude Aspremont à M. Pichard, chanoine théologal de l’église cathédrale de Périgueux, au sujet du”docte escrit du télescope de M. Tarde’” (1630), listed in Lauer, op cit., II , p. 51, no. 92, fol. 53; and Gabriel Tarde, “Observations au sujet des astres de Borbon du chanoine Tarde,” in Bulletin de la Société historique et archéologique du Périgord, 4 (1877), 169 – 173. Gassendi’s letter to Galileo is in Galileo Galilei, Le opere, A. Favaro, ed., XIII (Florence, 1903: repr. 1935), no. 1729, lines 56–64: and Gassendi, Opera omnia (Stuttgart, 1964; repr. of Lyons, 1658 ed.), VI , 5.