VOL. LXXVII.] 



PHILOSOPHICAL TRANSACTIONS. 



227 



I shall now give the apparent zenith distance of the equator, and the true lati- 

 tude of the observatory, resulting in this manner from my observations of 6 

 years, from the autumnal equinox of 1765 to that of 1771? in which I allowed 

 0'^9 for the correction of the error of the line of collimation, additive to the ob- 

 served zenith distances, as I found from a revision of my calculations of the zenith 

 distances of stars taken with the mural quadrant, compared with the like taken 

 with the zenith sector in 1768. 



Years of the observations. 



Autumnal equinox of 1765 and vernal of I766 

 Autumnal equinox of 17 66 and vernal of 1767 



Both equinoxes of 1 768 



Both equinoxes of 1769 



Both equinoxes of 1770 



Both equinoxes of 1771 



o a 



to O 



n3 > 



52 

 38 

 46 

 48 

 20 

 42 



■} 



Apparent zenith 

 distance of equa- 

 tor, taking the 

 sun's horizontal 

 parallax 8".8. 



51 

 51 



28 

 28 



41.3 

 39.5 



51 28 40.7 



Mean from 6 years observations 



Mean found by Dr. Bradley, with Q's horizontal pa-l 

 rallax 10^" / 



But if 1".2 be added to reduce them to the O's hori- 

 zontal parallax 8".8, Dr. Bradley's result will be 

 changed to 



Differing from my determination above only .... 



In further confirmation of the latitude of the Observatory, I shall now adduce 

 8 years observed zenith distances of the sun in the solstices, being deduced from a 

 number of observations taken at and near the solstices, and corrected for line of 

 collimation, refraction, parallax, and nutation. 



True latitude of the 

 Observatory, ac- 

 cording to Dr. 

 Bradley's refrac- 

 tions and the sun's 

 horizontal parallax 

 8".8. 



51 28 



40.1 

 41.9 

 43.7 

 40.3 

 40.8 

 41.3 



0.6 



Years of 

 observa- 

 tions. 



1765 

 1766 



1767 



1768 

 1769 

 1770 

 1771 



1772 



Mean 

 Latitude 



Summer solstitial 

 zenith distance re- 

 duced. 



N° of 

 days of 



obser- 

 vations. 



28 



30.2 

 33.6 



32.0 



29.7 

 31,8 

 30.7 

 32.0 

 31.8 



28 

 51 





 28 



31.5 

 40 



6 



8 

 7 

 8 

 12 



Winter solstitial 

 zenith distance. 



74 50 



46.1 



48.8 



uncertain 



from an 



accident. 



44.9 



46.2 



44.1 



42.2 



r uncertain "» 

 < from an > 

 L accident. J 



N° of 

 days of Half sum or lati 



obser- tude of the place, 

 vations 



51 28 



38.2 

 41.2 



37.3 

 39.0 

 37.4 

 37.1 



Half difference or 

 obliquity of the 

 ecliptic. 



23 28 



8.0 

 7.6 



7.6 

 7.2 

 6.7 

 5.1 



4ij.:2 y a/. I 5.1 



Line of collimation altered by applying an achromatic object- 

 glass to the telescope. 



74 56 45.4 



51 28 38,4 



23 28 7.0 

 On Jan. 1, 17 69. 



23 28 8.5 mean obliquity of ecliptic on Jan. 1, 1769. 



GG 2 



