Reducing Personal Equation (1 results)

Regiomonti (Königsberg), Frid. Nicolovium, 1818. Folio. Near contemp. hcalf. Gilt spine with gilt lettering. A small nick at upper backhinge. (12),325,(1) pp. Light scattered brownspots. Top of title-page with old owners name and a small stamp. First edition of this milestone work in astronomical obeservation, where Bessel reduced the observations for the "personal equation" based on Bradley's observations and here published Bradley's Greenwich observations for the first time and making a catalogue of 3222 stars extracted from them."The positions of Bradley?s stars valid for 1755 were published by Bessel as Fundamenta astronomiae pro anno 1755 (1818). This work also gives the proper motions of the stars, as derived from these observations of Bradley, of Piazzi, and of Bessel himself. It constitutes a milestone in the history of astronomical observations, for until then positions of stars could not be given with comparable accuracy: through Bessel?s work, Bradley?s observations were made to mark the beginning of modern astrometry. During this investigation Bessel became an admirer of the art of observation as practiced by Bradley" and because Bradley could not evaluate his own observations, Bessel followed and also taught the principle that immediately after an observation, the reduction had to be done by the observer himself. Further, he realized that the accurate determination of the motions of the planets and the stars required continuous observations of their positions until such motions could be used to predict "the positions of the stars . for all times with sufficient accuracy." (DSB).Shapley a. Howarth. A Source Boook in Astronomy, p. 103 a. 216.