360 A Short History of Astronomy [CH. xiii. 



under die title Fundamenta Astronomiae, of a catalogue of 

 the places of 3,222 stars as they were in 1755. A. special 

 problem dealt with in the course of the work was that of 

 refraction. Although the complete theoretical solution 

 was then as now unattainable, Bessel succeeded in con- 

 structing a table of refractions which agreed very closely 

 with observation and was presented in such a form that 

 the necessary correction for a star in almost any position 

 could be obtained with very little trouble. His general 

 methods of reduction published finally in his Tabulae 

 Regiomontanae (1830) also had the great advantage of 

 arranging the necessary calculations in such a way that 

 they could be performed with very little labour and by an 

 almost mechanical process, such as could easily be carried 

 out by a moderately skilled assistant. In addition to 

 editing Bradley's observations, Bessel undertook a fresh 

 series of observations of his own, executed between the 

 years 1821 and 1833, upon which were based two new 

 catalogues, containing about 62,000 stars, which appeared 

 after his death. 



278. The most memorable of Bessel's special pieces of 



a: 

 FIG. 85. 6 1 Cygniand the two neighbouring stars used by Bessel. 



work was the first definite detection of the parallax of a 

 fixed star. He abandoned the test of brightness as an 



