121 



a Lyrae, and is not quite 13° distant in declination from it. 

 Therefore if any unknown cause should occasion an appear- 

 ance of parallax, and render the observations of a Lyrae in- 

 accurate, the same ought to affect the observations of y Dra- 

 conis in a similar way. But the above results shevv that it is 

 not the case, and consequently afford a powerful argument 

 that the difference of the zenith distances of a. Lyrs in sum- 

 mer and winter is occasioned by parallax. 



The above 58 observations give the 



mean N. P. D. Jan. 1, 1813, 38° 29' 3",o8 



By the former determination 3 ,70 



« Lj'fSB. 



Bj' 20 observations In June, July and 

 August, 1814, the mean zenith dis- 

 tance, Jan. 1,18I4 14" 46' lO",87+,78 /> 



By 20 observations in Decern. 1814, 

 January and February, 1815, the 

 mean zenith distance, Jan. 1, 1814, 14 4(5 12,00 — ,78p 



Hence p ?p >77ii^ ,:b7=vO":,72. 



o 



In computing the above observations the French refrac- 

 tions were used. In the former computation of theobserva- 

 tions of a. Lyrs, Bradley's refractions were used. Had ihe 

 French refractions been used, the parallax, as was observetl, 

 would have been 2", or p= 1". Combining the forHier'126' 



VOL. XII. s 



