Responsio ad Additiunculam D. Ioannis Kepleri, Caesarei Mathematiici, praefixam Ephemeridi eius in annum 1624. In qua cum de totius Astronomiae Restitutione, tum imprimis de observatione diametri solis, fide tubi dioptrici, eclipsibus utriusque luminaris, luculenter agitur

HORTENSIUS, Martinus [Martin van Den Hove]

Published by Jean Maire, Leiden, 1631

On His Calculations About the Size of the Sun. First edition, extremely rare, of this work concerning the angular diameter of the Sun, in which Hortensius was in dispute with Johannes Kepler. This was important, because of its relevance to the determination of the degree of ellipticity of the Earth's orbit, which Kepler had investigated using the observations of Mars in the Astronomia nova (1609). "According to Kepler's theory, the eccentricity of the Earth's orbit as determined by the traditional method needed to be bisected, and Kepler had supported this proposition by observations of the Sun's apparent diameter at aphelion and perihelion. In 1630, in a preface to Phillipe van Lansberge's Commentationes in motuum terrae ., Hortensius challenged Kepler's observational results, claiming a much larger ratio between observed diameters at perihelion and aphelion than Kepler had found. In addition, Hortensius objected to Kepler's reduction of solar parallax to 1', about one-third of the traditional value, and to Kepler's indulgence in harmonic speculations to support this reduction. Kepler responded in the 'Addiuncula' that he prefixed to the ephemerides for 1624, arguing that if determination of apparent solar diameters is carried out in accordance with a proper understanding of the optics of the camera obscura, the results will bear out the bisection of the eccentricity" (Wilson, p. 64). "By using one of the primitive telescopes of the time and studying solar eclipses, he found the solar angular diameter to be 36â at perigee and 33â 34â at apogee, with a ratio of 1.072. Kepler, on the other hand, believed that a telescope distorted the image and preferred to employ a small hole at the end of a long tube; he found a mean value of 30â and a ratio 1.033 (actual values: 32â 04â and 1.034). This question was of great importance, because it was directly connected to the matter of the eccentricity of the earth's orbit, which Kepler had investigated by using observations of Mars. Kepler was vehement regarding this issue and used untenable arguments; Hortensius responded politely [in the present work] but suggested that Kepler might have altered the observational results in order to get agreement" (DSB). The complete text of the 'Addiuncula' is reprinted in Hortensius' Responsio. OCLC records only University of Texas, Austin, in North America. Not on RBH. Provenance: 'Wilson' (bookplate on front paste-down), probably Curtis Wilson (1921-2012), historian of astronomy. Wilson graduated Phi Beta Kappa from UCLA in 1945 with a B.A. degree in History and received his M.A. degree (1947) and his PhD degree (1952) in History of Science from Columbia University. He spent most of his career teaching at St. John's College in Annapolis, Maryland, starting in 1948 and retiring in 1988. He was editor and original contributor to Volumes 2A and 2B of the General History of Astronomy. Pierre Gassendi became embroiled in the controversy between Hortensius and Kepler, following the publication of Gassendi's Mercurius in sole visus (1632). "The observation of Mercury's transit takes on remarkable significance and interest in the context of the very heated discussion between Kepler and Isaac Beeckman's young disciple, Martinus Hortensius (Martin van Den Hove), about the reliability of telescopic observations. As soon as Gassendi's Mercurius was published, Hortensius praised his sense of observation and even enlisted Gassendi in the campaign he himself led against Kepler, against whom he directed some very harsh words. Kepler, according to Hortensius, lacked geometric evidence-which must be the rule of truth in any human knowledge-and made arbitrary physical assumptions to explain the inconsistencies of his observations. Hortensius had written an important preface to his Latin translation of Johan Philip Lansbergen's Commentationes in motum terrae diurnum et annuum. Here Hortensius targets very precisely Kepler's observations of the Sun, the determinati. Seller Inventory # 6205

Bibliographic Details

Title: Responsio ad Additiunculam D. Ioannis ...
Publisher: Jean Maire, Leiden
Publication Date: 1631
Edition: First edition.