COMMENTATIO ASTRONOMICA. 241 



ti inlercepted arches are compared. Bul admilting the divisions of the Greenwich cir- 

 « clc to be as accurale as human ability could execule them , it is not to be expecled 

 V the cffecls of different positions of the telescope will not be visible in such small quan- 

 « tities.as are the objecls of our inquiry. Therefore the arches only have been compa- 

 « red , when the position of Ihe telescope was the same in bolh suinmer and winter. 

 « The results of three years are ; 



Summer - inlercepted arch - Winter. Diff. 



49° 42' 10",49 49' 42' 12",48 1",99 



12, 10 13, 92 1,'82 



13, 61 15, 70 2, 09 



« These intercepted arches between et Lyrae and Polaris are reduced to Jan. 1 1815. 



« lusteed of using the intercepted arches we may proceed another way , which must 

 « necessarily lead us to the same conclusions, but which will enable us to examine mo- 

 « re satisfactorily the results given by the instrument during a considerable period. " 



« If to the observations of the pole-star, reduced by the common equations, we 

 « apply the polar distance of the pole-star as given in the Standard catalogue , we ob- 

 « lain the corrections for index error. Applying these to the observations of « Lyrae , 

 X( each being reduced to a given lime ( 1 Jan. 1815) , we shall have a numerous series 

 w of observations of « Lyrae for our consideralion. Then comparing the summer ob- 

 V servations with those in the winter, we deduce the effects of parallas. It is obvious 

 « Ihis conclusion will not be affected by any error in the Standard catalogue. The only 

 « cause of applying the Standard catalogue is to be able to refer each observations of 

 K « Lyrae to a Single point in the manner we refer by our circle a star to the zenith 

 K point. " 



« In Ihis manner, with the Greenwich circle and by Bradley's refractions, « Lyrae: 



1813 , 6 micr. 46 summer and 22 winter observations give p = 1",41 



1814, 2 « 32 « « 33 « « k p = 1, 18 



1815, 2 « 42 « « 46 « a « p = 1, 46 



« "When the reductions are made by my own table of refractions ( the same in quan- 

 « tity as the French), the results become : 



«for 1813.. /J=rl",12, for 1814.. p = l ",01, for 1815.. ^5= 1",16, mean. .^s = I",10, 

 « by the Greenwich circle." 

 « The result of all my observations by the Dublin circle , as given in my paper on 

 nutation , is p = 1",12." 



Hh <, The 



