Curious Astronomical Fact. 231 



M. Bessel has met with a similar circumstance at the ob- 

 servatory at Konigsberg. During the visit of the late Dr. 

 Walbeck to that place in the winter of 1820-21, these two 

 astronomers instituted a set of comparative observations on 

 the following stars : 



954 Mayeri x Piscium 



<J> Aquarii 971 Mayeri 



y Piscium xxiii. 136 Piazzi 



b 147 



962 Mayeri 979 Mayeri 



The right ascensions of these stars were observed by them 

 alternately, with the same instrument, for several days ; and 

 the result was (taking a mean of the whole number of obser- 

 vations) that Dr. Walbeck observed them l".041 in time later 

 than M. Bessel. The observations were made with the me- 

 ridian circle of the observatory, and with a power of 182. 

 We have not room, in this extract, to give more than the re- 

 sults : the detail of the observations occupies several folio 

 pages in the work above alluded to. 



He then proceeds to mention some comparisons that were 

 made with M. Argelander of Abo, by which he finds that this 

 astronomer observed the right ascensions of several stars in 

 the constellation Gemini, l".223 in time later than M. Bessel. 



The comparisons made between Dr. Struve and M. Bessel 

 are the most singular: in 1814 the difference was 0".044 ; in 

 1821 it was 0".799; and in 1823 it was 1".021. By a direct 

 comparison of the culmination of a Piscis Australis on Nov. 13, 

 1 820, the difference was '.68. 



Other comparisons were afterwards made between the ob- 

 servations of Dr. Struve and Dr. Walbeck ; and between Dr. 

 Struve and M. Argelander * : and the result of the whole is 

 shown in the following table ; where the names of the above- 

 mentioned observers are denoted by their initial letters. 

 B — W= -1".041 /— 0".044 in 1814 



B — A = — 1 .223 r_«j_5— ° -680 1820 



S— W= -0.242 i— 0.799 1821 



S — A = —0.202 f— 1.021 1823 



From some experiments which were afterwards made, 

 M. Bessel seems to think that a part of this difference may 

 arise from the peculiar mode, which each observer may adopt, 

 of counting the time by his ear, whilst he is watching the 

 motion of the star with his eye. For, by trying a half-second 

 pendulum clock, some of these differences vanished ; and 



• The detail of these experiments is also given by Dr. Struve himself, in 

 the 3rd vol. of the Dorpat Observations, pages L and 42. 



others 



