210 GERARDI REGNERI FOCKENS 



« In ihe Ihird place , ihe aberralion of light , Ihough best known of all , may also be 

 .« liable to some small errors, since tlic observalions froni wliich il was deduccd labuu- 

 « red under all the foregoing difficulties. I do not mean lo say , Ihat cur Iheories of 

 ~ ( all ihese causes of error are defective ; on the contiary , I grant Ihat we are for rnost 

 « astronomical purposes sufficiently furnished witli excellent tables to correcl our obser- 

 « vations from the above menlioned errors. But when we are upon so delicate a 

 v point as Ihe parallax of Ihe stars; when we are in-vesligaling aiigles that may, per- 

 <i haps, not amount lo a Single second, wo musl endeavour lo keep clear of every 

 « possibiliiy of being involved in unceriainties ; eveii die hundieth part of a secoud be- 

 « comes a quaniity lo be laken into considerati on. " 



Deinde aiuera. meihodum suam indicat, quam suis verbis descripsimus P. II, C. III, 

 § 9. 



Haec itaque commeutatio, quae est e primis, quas frequeniissimas Herschelius So- 

 eieiaii Regiae cummunicavit , etsi nullas in ipsa parailasi observationes factas exhibcal , 

 nibilo secius tum rebus aliis insignis est , tum vero inprimis semina habet, unde siellarum 

 duplicium observationes, ad hoc usque lerapus aiquein dies frequentius instiiutae, orlum 

 ccperint. Quomodo autera cum bac cohaereat HerscheliiyJ/^d scriptio mos laudanda , 

 eo tempore , quo laudeiur , indicabiiur. 



Gaeterum, anteaquam saeculum mittam antecedens, ad annum 1792 annotandum est, 

 CI. S ch u bort quaedam Iheoretica circa parallaxin publici juris fecisse (•). 



Hunc enim scriptio Herschelii adverterat ad parallaxin. Ergo primura , quid hucus- 

 que asironomi hac in re praestiterint , indicat; Hersclielium laudat , duplicibus siel- 

 lis ad parallaxin usum , quibus ad proprium motum usus fuerat Tobias Mayerus; 

 meihodum Angli breviter indicat. 



« Die Vorzüge dieser Methoden fallen in die Augen und es wird nicht überflüssig seyn, 

 « dieze Rechnung zu entwickeln, nachdem nocli einige allgemeine Anmerkungen über 

 « dieze wichtige Materien voraus geschikt sind. " 



Hae animadversiones referuniur ad quatuor quaniilales r, p, verum et apparenl«m 



siellat diametrum; ar, |, veram et apparentem slellae distantiam; quac cum «, radio 



orbilae tenrestris , bis aequaiionibus copulantur: 



r z^ xp a z= x^ 



in quibus p et ^, quae est p.irallaxis ipsa, observaiionibus simt determinandae. Jara 



vero secundum Bradleium maxiraum ponit l" pro § et 1" pro p, minimum autem 



probabili ratiocinio quacrit. 



Dein« 



(*) Berliner Astronomisches Jahrbuch, 1796. p. ii3. Titulus est: Ueher die Parallaxe der Fixster- 

 . ne, von Herrn Professor öcbubert in Petersburg, unterm 24 November 179;» eingesandt. 



