230 GERA P> DI REGNERI FOCKENS 



(, I hnve bcen able lo oblain some resulls Ihal I shall nolice farlher on , which ap- 

 (v near to coincide wilh my former ones as lo a Aquilae, in a remarkable manner; 

 « and it is to Ihis slar Ihat we are , I lliink , to lock f jr Ihe final decision of the ques- 

 « lion. As to » Lyrae and Arclurus, my resulls have nol been so uniform as I had ex- 

 « pecied from my former obscrvalions; but as lo a, Cygni , my recenl observations are 

 « consislcnt with my former ones , in exliibiliog the same discordance between Ihe sum- 

 « mer and winter observations as before, which appeared to me to point out a paral- 

 « lax for that star, but Icss than for any of Ihe olher three Stars. The resulls of the 

 « observations of Mr. Pond, by the fised telescope , as given in the last volume of the 

 « Transactions , appear , at first sight , very decisive againsl Ihe existence of any visiblc 

 « parallax in« Cygni; but in considering these observations, a dilTiculty suggpsts ilself, 

 « which if füunded , will rendcr ihe result deduced from a Cygni and ß Aurigae quite 

 « inconclusive. This and some olher poinls relative to the fixed telescopes, will be no- 

 « liced farlher on. " . . • . 



« I am led to entertain doubts of the filness of an Instrument similar to the Greenwich 

 « mural circlc, for this delicale cnquiry." . . . 



« IHy reasons for enlerlaining ihese doubts , will appear in the following remarks re- 

 « specliiig the elements used in Computing the index error, in instruments similar to the 

 K Greenwich mural circle. " 



<i The polar dislance of a star, as observed by a mural circle, requires, besides the 

 « correction for refraclion , aberration , annual yariation , etc. also the application of 

 V the indes error." 



« This index error is delermined by the meau of resulls deduced from observations of 

 « Stars of the Standard calalogue. 

 <t Let i r= index error, 



d =: mean polar dislance of a star of the Standard catalogue deduced fron» 



Observation, 

 c z^ mean polar distaiice of Ihe samc star in the catalogue. 

 « Then t =z d — c 

 « Let o =:; observnd polar dislance, 

 r = refraclion. 

 p zr parallax. 

 a = aberralion of lighU 

 n == nutalion. 

 9 = semianhual equatiou. 

 V = annual Variation. 

 « Theu izizo+r + p + a + n-^'S + V'^ 



« the- 



