4a 



Let p. represent the semiannual parallax of « Lyras. 



Mean Zen. Dist. 



a / // 



Then by the first 20 observations near opposition J* 46 19,51 -\-,76p 



fay next 20 .... 19,07-l-,82p 



by next 25 .... 19,26 + ,75p 



Mean of 65 observations near opposition 14 46 19,28 + ,78;? 



By first 20 observations near conjunction - 14 46 20,84 — ,72p 



by next 20 - - - - 21,24— ,8Ip 



by next 21 . . - - - 2l,0l_,85p 



Mean of 61 observations near conjunction 14 46 21,03 — ,79^ 



Hence 19",28p.+,78p = '2l"fi3—,79P' 

 orp = 1 ,1 

 and the parallax of the annual orbit for «■ Lyrae = 2",2. 



Thus the mean zenith distance 

 of « Lyr^, Jan. 1, 1811, by 126 observations = 14 46 20,15 



By the 26 observations, near 6 o'clock in the evening, 

 the mean zenith distance, Jan. 1, 1811=14 4b' 20", 'i 5 — , op. 



If the above conclusion respecting the parallax of a. Lyra? 

 be 'not admitted, some explanation of the differences of the 

 zenith distances must be sought for. 



First, it cannot arise from errors of observation, compre- 

 hending error of adjustment in the vertical axis, error of bi- 

 section of the star, and errors of reading off. These errors by 

 their nature are corrected by taking a mean of repeated ob- 



