536; .G E R A R D I R E G N E R I F C K E N S" 



Aurigae ß. Sum. DifT. of tu and 3 Cygn;.,; 



9",8I8 = 17",! 84 5",226 



10, 044 J7, 964 



14, 823 IS 163 5, 287 



14, 067 18, 142 



12, 529 18, 174 5, 432 



■ « These observations seem to me lo prove bayond a düubt that the parallax of x, Cyg- 

 « ni cannot much exceed onelenlh of a second of a degree. " 



Paulo postautem, 13 Febr. 1819, ila Brinkleius scribit (*): 



« The observations of Mr. Pond with the fixed telescope, may be adduced as conirary 

 V lo my results ; because with Ihis maximum of aberration , bis summer and winler dif- 

 « ferenoes of N. P. distance of ß Aurigae and a, Cygni would.differ by 1" in a di- 

 « rection conirary to parallax. But it also seems to show the necessity of exact deler- 

 « minalion of the precise quanlities of tlie equations for N. P. D. before any conclusivc 

 « arguments respecting the non-existence of parallax , from observations of the positiona- 

 « of -Stars relative to each other , can be adduced. In observations by the eightfeefc 

 « circle Ihis is not so necessary , as has been before mentioned .... 



« It appears to me, that the only melhod by which an explanslion of the difficulties 

 « that have occurred , from a comparison of the Greenwich observations and of Ihose 

 « made at Ihis Observalory , can be obtained , is from an extensive series of Observation» 

 d of many stars, referring each to the apparent zenith point. 1 am therefore pursuing' 

 M. such a course of observations. Conclusions as to the existence or non-existence of pa- 

 «rallax, from comparisons of the relative places of siars takeu indiscriminately , must 

 « be liable to much uncertainty, wbether Ihe comparisons be made by polar distance» 

 « or by right ascensions. The former being affected by the uncertainty of refraction , 

 «may, at first view, be thought more subjcct to error than tlie lalter; but a carefuJ 

 « consideration of the circumstances attending the latter melhod , will show lliat it ha» 

 « its peculiar difRculties." 



« As Mr. Bessel's determination of the maximum of aberralion has been referred lo , 

 « (in the same paper ) it may also be right lo menlion Ins results respecting the parallax 

 « of certain stars. He uses transit observations of slars nearly opposite in riglit ascen- 

 « sion. Thus he finds the sum of the parallaxes of Sirius and x Lyrae insensible , and- 

 « the sum of the semi-parallaxes of Procyon and « Aquilae, nearly 1". Ibis melhod of 



« using 



(*)Phil. Trans. 1819. P. II. p. 1141. Tom. CIX, xvnj Titulus est: The results of Observations 

 made at the Obsenatory of Trinitj College, Dublin, Sy the Rev, J, BrinkUy, 



