Königsberg: Friedrich Nicolovius, 1818.
A fine copy of this work which “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” (Walter Fricke in DSB). Norman 226; Honeyman 311.
“In 1807 Olbers encouraged [Bessel] to do a reduction of Bradley’s observations of the positions of 3,222 stars, which had been made from 1750 to 1762 at the Royal Greenwich Observatory. This task led to one of his greatest achievements ...
“Bessel recognized that Bradley’s observations gave a system of very accurate star positions for the epoch 1755 and that this could be utilized in two ways. First, a reference system for the measurement of positions of stars and planets was required. Second, the study of star motions necessitated the determination of accurate positions for the earliest possible epoch. Tobias Mayer had determined fundamental star positions from his own observations around the middle of the eighteenth century, but Bradley was never able to reduce his own numerous observations.
“The observations of star positions had to be freed of instrumental errors, insofar as these could be determined from the measurements themselves, and of errors caused by the earth’s atmosphere (refraction). The apparent star positions at the time of a particular observation (observation epoch) had to be reduced to a common point in time (mean epoch) so that they would be freed of the effects of the motion of the earth and of the site of observation. For this a knowledge of the precession the nutation, and the aberration was necessary. Bessel determined the latitude of Greenwich for the mean epoch 1755 and the obliquity of the ecliptic, as well as the constants of precession, nutation, and aberration. To determine precession from proper motions, Bessel used both Bradley’s and Piazzi’s observations ...
“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)
Houzeau & Lancaster 10117.
Slim folio: 330x190 mm. Fine contemporary red moiré boards with gilt-lettered spine. Pp.   3-325 [1:errata]. Internally clean, rare in such good condition.