COMMENTATIO ASTRONOMICA. 75" 



Exemplum conversionis detectique collimandi erroris hoc esto: 



Tempus. Barom. Thermom. Stella. Pos. Transilus. Distantia zenilh. 



1. 2. 



1815 Aug. 1 29P,946 78j,0 678,7 P. 339. XX. Dir. 20h43™30',3 e2°33'31",0 



2 29, 966 77, 5 66,7 Inv. 20 43 31,2 6i 32 18, 



Stella est Catalogi Piazzini (1814) XX»» 339', ila definila: 



1800 a = 310M8'58" rf = 21°34'17",5 



Jam vero observationes hae, secum invicem comparatae, exhibent collimationis errorem 

 ± 36'',5 , qui signo superiori ad inversas , inferiori autem ad directas , omnium stellarum 

 «emel observatas distantias a zenilho erit applicanda. 



De circulo Menapiensi autem congessi quaedam hoc loco memoranda. Brinkleius 

 quidem ipse circulum descripsit. Sed liber non adest. Primum Pearsonus ila de eo lo- 



quitur ( ' ) : 



« This instrument , in the hands of one of the first theorelic and practica! astronomers 

 « of the age, has put itself in competition wilh Ihe more recent circles erected at 

 « Greenwich by Troughton and T. Jones; and up to Ihe present moment disputes wilh 

 « them the claim to accuracy, with respect to that Single seeond which constitules the 

 « apparently existing difference between them , as it regards Ihe subject of parallax of 

 « certain stars in north polas dislance ; sub judice lis est. "... 



« The desirable property , that this construction of a circular instrument possesses , of 

 « obviating the effecl of ist own errors , including that of collimation in zenilh distan- 

 «ce, by a reversion of its position, has been duly appreciated and insisted on by the 

 « leamed and dignified professor, who has experienced not only the Utility but the con- 

 « venience of such property. Each double Observation is thus independent and con- 

 « clusivc. "... 



« The •well known contest on the subject of annual parallax, that has existed for the 

 « last few years between Mr. Pond and Dr. Brinkley , has called forlh extraordinary exer- 

 « lion of taleut and assiduily, bolh in making and reducing the respeclive observalions; 

 ,« and it slill remains a matter undetermined whether Ihe trifling difference , arising 

 « from a comparison of the respeclive conclusions , is occasioned by the instrumenta 

 « themselves, or by Ihe labular corrections which have been applied as reductions. 

 ¥ None but instruments of Ihe highest order can compete , in delermining the limit of 

 « accuracy ihat is allainable in observalions of such cxtrarordinary delicacy, that all 

 « the sources of error may be reduced wilhix» the compas^ of a Single ^econd. In Dr. 



« Brink- 



(•) Pract. Astron. II. 4^3, sqq. , .; w.l "v;- .1 . 



K 2 



