CHAP. III., 3.] 



ASTRONOMY. BESSEL MR AIRY. 



51 



(224.) 

 Results. 



(225.) 

 Bessel's 

 jwn obser- 

 vations. 





(226.) 

 His numer- 

 )us works 



>n astrono- 

 my- 



the places of wandering bodies to standard 

 points. 



Bessel's work includes a methodical reduction of 

 the places of above 3000 stars observed by Bradley, 

 and an investigation of the sun's apparent path, to- 

 gether with a full discussion of the principles and 

 application of every correction, instrumental and 

 uranographical, which such observations require, and 

 which are applicable to all others of the same kind. 

 It includes, therefore, dissertations on some of the 

 most delicate points of Astronomy, and " Constants" 

 for the different corrections, which, with slight varia- 

 tion, have been since employed in every observatory. 

 Bessel devised also a remarkably simple mode of find- 

 ing for each star the varying corrections of its place. 

 The proper motions of the stars were also determined 

 for the first time with approximate exactness, by 

 comparing Bradley's places with more modern ob- 

 servations. 



In subsequent years (the Fundamenta were pub- 

 lished in 1818) Bessel contributed to the science of 

 astronomy numerous and regular observations of the 

 heavenly bodies ; the Annals of the Konigsberg 

 Observatory were regularly published from 1814, 

 being (I believe) the first foreign establishment 

 which followed the example set by Maskelyne at 

 Greenwich, with the important addition of systematic 

 reduction. 



Of the subsequent labours of Bessel we must speak 

 very shortly. The determination of the parallax of 

 the star called 61 Cygni, perhaps the most original 

 and important of these, we shall refer to another sec- 

 tion, where we shall compare it with the results ob- 

 tained by other astronomers. He made interesting 

 physical observations on Halley's comet at its return 

 in 1835; he prepared the materials for a very ex- 

 tended catalogue of fixed stars, arranged in zones, 

 more recently published by Professor Weisse. In 

 connection with the theory of the pendulum as a 

 measure of gravity, he repeated and extended Newton's 

 important experiments on the uniformity of the gra- 

 vitating force on all kinds of matter ; he applied a 

 new correction to the vibrations of the pendulum, and 

 improved the method of observing them correctly; 

 and he discussed with his habitual mathematical skill 

 and elaborate perseverance the figure of the Earth, 

 from the whole of the then existing observations ; 

 whilst he also directed an operation for connecting 

 the Russian triangulations with those of western 

 Europe, a delicate task, which he performed with 

 consummate skill. It will thus be seen that (without 

 mentioning a host of minor works and memoirs) there 

 was hardly a great department of Astronomy in which 

 Bessel did not take a distinguished part. Even the 

 discovery of Neptune, by calculation from the irregu- 

 larities of Uranus, was contemplated as a practicable 

 problem by the veteran astronomer in his later years. 

 He died on the 17th March 1846 ; therefore only a 

 few months previous to the publication of MM. Le- 



verrier and Adams' discoveries, and their triumphant 

 consummation by M. Galle. 



Even before Bessel's career as an astronomer had (227.) 

 properly commenced, Pond, in England, had antici- P nd > the 



, j . i ., , . Astrono- 



pated, in a good measure, the improvements m prac- mer -Royal, 

 tical astronomy to which we have referred in the an excel- 

 beginning of this section. Already, in the earliest lent ob - 

 years of this century, he had made observations at his server> 

 private residence with a comparatively small circular 

 instrument by Troughton, which led him to detect the 

 gradually increasing errors of Bradley's quadrant still 

 in use at Greenwich, and to recommend the adoption 

 of complete circles (disused since the time of Rb'mer) 

 and the specific examination of errors of division. 

 These principles he carried out at Greenwich, to which 

 establishment he was afterwards appointed. His very 

 indifferent health prevented that incessant activity 

 which the management of a first-rate observatory re- - 

 quires; nevertheless, he is justly regarded as one of the 

 chief reformers of the practical astronomy of those 

 days. 



His successor, Mr Airy, has distinguished himself (228.) 

 by a more active career. Endowed with very un- Succeeded 

 common abilities, and with great physical powers of A y ir r 

 endurance, he has, from his youth, been ever foremost 

 not only in promoting, in every one of its departments, 

 his favourite science of Astronomy, but also many 

 other allied subjects, particularly Optics, to which we 

 shall have occasion to refer in another section. 



Born in the county of Northumberland in 1801, (229.) 

 Mr GEORGE BIDDELL AIRY acquired great distinction His numer - 

 at Cambridge, where he graduated in 1823, and was ^phpilT 

 appointed to the charge of the Observatory there in and practi- 

 1828, after the death of Professor Woodhouse, a per- cal astro- 

 son sincerely attached to astronomy and well skilled in nom y- 

 it, yet one who did not succeed in imparting much in- 

 teresteither to its theoretical or practical departments. 

 Mr Airy engaged in the important investigation of a 

 new irregularity in the motion of the Earth and 

 Venus, to which I have referred in the chapter on 

 Physical Astronomy (114), and at the same time he 

 undertook to publish his own Observations in regular 

 annual volumes, including a complete comparison 

 of the results with the best tables, thus presenting 

 at a glance the existing errors of theory. This prac- 

 tice he introduced at Greenwich on succeeding Pond 

 there in 1835; and he has pursued it ever since. 

 But not contented with rendering the annals of the 

 National Observatory a correct reflection of the state 

 of the heavens in his own day, and also of the con- 

 dition of Astronomical Theories, he did not rest until 

 he had performed for the observations of his prede- 

 cessors the same service, and thus produced a series 

 of comparisons of the observed and calculated places 

 of the moon and planets, unexampled for extent and 

 accuracy. Beginning with Bradley's Observations 

 in 1750, he investigated and applied all the instru- 

 mental and uranographical corrections to each, as 

 Bessel had done for the observations of the sun and 



