Der Bericht Der Englischen Sonnenfinsternisexpedition üBer Die Ablenkung Des Lichtes Im Gravitationsfelde Der Sonne, Pp. 667-673 In: Die Naturwissenschaften, Achter Jahrgung, Heft 34, 20 August 1920. The First German Report Of The Eddington Eclipse Expedition Freundlich, Erwin Finlay

First edition, journal issue in original printed wrappers, of the first German report of the British expeditions led by Eddington, Dyson and Davidson in 1919 to measure how much background starlight is bent as it passes the Sun. The results showed that the measured deflection matched the theoretical prediction of Einstein's General Theory of Relativity. Einstein became world famous on 7 November 1919, following press publication of a meeting held in London on 6 November 1919 where the results were announced. Freundlich (1885-1964) was uniquely well qualified to write a report on the expeditions for German readers. In July 1910 he had been appointed assistant at the Royal Observatory in Berlin. In the following year Einstein requested Freundlich's cooperation in observing the motion of the planet Mercury. Freundlich's observations fully confirmed earlier evidence for a discrepancy in Mercury's predicted orbit, as Einstein had expected on the basis of general relativity. In 1914 Freundlich attempted his own observations of the bending of light during the solar eclipse at Feodosiya in the Crimea, but the expedition had to be abandoned owing to the outbreak of World War I. Freundlich also suggested measuring the gravitational red-shift - according to general relativity the wavelength of light should be increased in the presence of a strong gravitational field such as that of a star. "Through his intimate contact with Einstein, Freundlich was the first to become thoroughly acquainted with the fundamental principles of the new gravitational theory and, as Einstein himself remarks in the foreword of Freundlich's book 'Die Grundlagen der Einsteinschen Gravitationstheorie' (Berlin, 1916), he was particularly well qualified as its exponent because he had been the first to attempt to put it to the test" (DSB). "After Eddington confirmed that Einstein's theory accounted quantitatively for the discrepancy in the position of the planet Mercury, on whose reality Freundlich had boldly insisted in 1913, the validity of the principle of relativity itself could no longer be doubted and Freundlich's scientific reputation was fully vindicated. Thus, in 1920, the Prussian Ministry of Culture decided to support the creation of the Einstein Institute at the Astrophysical Observatory, Potsdam; Freundlich was appointed observer in 1921 and later chief observer and professor of astrophysics. This institute was designed specifically to strengthen the empirical foundations of Einstein's gravitational theory and was equipped with an astrophysical laboratory and a powerful tower telescope for solar work, the Einsteinturm. Here, from 1921 to 1933, Freundlich encouraged his co-workers to tackle problems that appeared at the time to be of particular significance in the solution of the solar red-shift problem, such as the origin of the ultraviolet cyanogen bands (1924) and the measurement of the center-to-limb variation in wavelength along different radii on the solar disk (1930). Simultaneously he was supervising the construction of specially designed equipment for observing light deflection; and he planned three further eclipse expeditions, two of which (in 1922 and 1926) were unsuccessful because of bad weather conditions. The third (to Sumatra in 1929) was a complete success even though the final result proved to be significantly in excess of what Einstein's theory had predicted" (ibid.). 4to, pp. i-ii, 667-690, iii-iv (browned, several small marginal chips and tears, not affecting text). Original printed wrappers. A good copy of a rare and fragile item.