COMPAKISON-STAKS. CX1X 



The fewness of the observations from most of the individual sources renders the determina- 

 tion of the constant differences for the results of the respective observers a matter of much 

 difficulty. And it was soon palpable that no trustworthy equation could be obtained for any 

 observer, which would hold even approximately both for the southern stars of the first Venus- 

 series and the northern stars of the three other series of observations. Nor did the several 

 equations to be found in the books appear altogether satisfactory, or accordant. 



The catalogue of Comparison-stars contains 148 stars, arranged and numbered in the order of 

 their right-ascensions. Of these, N os - 135, inclusive, belong to the first Mars-series, and are 

 all situated between 24 and 26 of north declination. 



Twenty- three stars, between N os - 47-86, inclusive, as well as N 08 ' 87-109, making 46 in all, 

 belong to the second Mars-series, and are between the declinations 19^ and 25 north. 



N os - 36-46, as well as seventeen stars between N os - 47-86, making thirty-nine in all, belong 

 to the second Venus-scries, and are situated between 14^ and 25 north declination. So that of 

 all these 109 stars, none are farther north than +26. 5, and none farther south than +14. 5. 



The first Venus-series, on the other hand, contains thirty-nine stars, N os - 110-148, all of 

 which are between 17^ and 28 of south declination, and comprised therefore within the 

 limits of Argelander's southern zones. 



Of the special lists, the Santiago determinations comprise the whole list of stars compared 

 with Mars during the second series of observations. 



The Washington determinations comprise the whole list of southern stars, with one exception, 

 (Venus, I,) and 25 northern ones 8 for Mars I, 17 for Mars II. 



The Cape determinations are for 12 stars observed with Mars I, and 3 observed with Mars II. 



The places from Bessel's zones are, of course, exclusively for northern, and those from Arge- 

 lander's exclusively for southern stars. 



The twenty stars from Riimker's catalogue are all northern. Those from the third Greenwich 

 catalogue, and all but one from the Twelve- Year, are northern. 



The stars from Lamont and Briinnow are all southern. 



From the positions taken from Lalande, 57 are for northern and 14 for southern stars. 



Of those from Piazzi, 20 are northern and 6 are southern stars. Of those from Taylor, 22 

 are northern and 5 are southern. 



Under these circumstances, it is manifestly most appropriate to refer the northern stars to 

 Bessel as the standard observer, and the southern to Argelander ; and this has been done, for 

 the sake of avoiding as much uncertainty as possible. In order to deduce the corrections neces- 

 sary for reducing the declinations to the standard, all those stars which have been determined 

 by two different authorities have been made to contribute to the result, and the mean difference 

 for each two observers computed when possible. 



Thus, we have for the Santiago (northern) determinations by 31 observations, 



Santiago Bessel = + 0".56 0".38, 

 and by 17 observations, 



Washington Santiago = + 1".06 0".23, 

 one observation being rejected in the latter case by Peirce's Criterion. 



The Greenwich catalogue of positions for 1850 gives by 23 observations, 



Bessel Greenwich = + 0".562 =h 0".503, 

 and by 8 observations, 



Washington Greenwich = + 0".66 0".36. 



Furthermore, we have from 20 observations (the same one being rejected as before,) 



Washington Bessel = + 0".44 0".59 ; 



and lastly, from 9 observations at the Cape, of which two were manifestly to be excluded, but, 

 by reason of their equality on the two sides of the mean, exerted no essential influence on the 

 result, 



Maclear Greenwich = + 0".39 0".31. 



