22 - CASSINI, Jean-Dominique (1626–1712).

CASSINI, Jean-Dominique (1626–1712). Letter signed “Cassini,” Paris, November 9, 1705, [to François de PLANTADE]; 2½ pages, in-4 (fold marks and a small wormhole at the bottom of the letter that does not affect the text). A beautiful and rare letter on astronomy. Description: The letter is addressed to his colleague in Montpellier, François de PLANTADE (1670–1741), an astronomer and advisor to the Court of Aides in Montpellier, where he founded the Academy of Sciences and Letters in 1706. “Having tested the two objective lenses made in the Netherlands against the sky, one of them proved to be very good, as did the accompanying eyepiece. He sent me a statement of the price of these lenses, which he says is as fair as possible. […] The price does not seem excessive to me, since he has sold lenses of lesser power at the same price. We were unable to obtain any with the precise length of 25 feet that you requested. I hope that the purity of your air will allow you to make observations that we have difficulty making here. Throughout the year, we see the principal stars of the first magnitude as they pass through the meridian, even when they are in conjunction with the Sun, provided they are at high latitudes—such as Sirius, Rigel, Arcturus, Capella, etc. As for the others that do not have a high latitude—such as the Eye of Taurus, the Ear of Virgo, the Heart of Scorpio, etc.—we see them at the meridian in broad daylight only when they are some distance from the Sun. There are times when they appear closer than at other times; this depends on the clarity of the air. As for Jupiter, we saw it about 34/ hours after sunrise with the naked eye, and we observed it at the meridian through the quarter-circle telescope half an hour before and after the Sun”… Abbé BIGNON met with the Bishop of Montpellier [Charles-Joachim de COLBERT] in Fontainebleau, “and they had a discussion there regarding your society. He will work to bring this matter to a close. He has determined that it is reasonable for you to be among the honorary members.” He returns to astronomy: “When the weather is clear, we continue to see the sunspots that were observed in the eastern part on the 4th of this month, and we have recently observed Saturn’s of Saturn (which is visible only during part of its revolution) for longer than we had previously observed during its other revolutions”…