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INTRODUCTION, Xxl 
TABLE 7.,—Determinations of the Values of Angle A. 
Readings of Horizontal Circle 
For Declination Telescope. For North Mark. 
Date. Angle A. 
Verniers. Verniers,. 
| Mean. Mean. 
A B (0) A. B Cc 
1841 7 wt ’ " , ” ° , ” , ” ’ 7 , ” ° , ” ° , u 
Aug. 7|| 55 10 o| 54 15-0| 54 40-0} 233 54 41-7|| 49 15-0| 49 55-0} 49 30-0] 77 49 33-7|| 23 54 52:0 
Sept. 4} 44 50-0| 45 20-0) 44 50-0 | 233 45 0-0|| 40 5-0| 40 5-0} 40 0-0) 77 40 3-3]) 23 55 3-3 
Sept. 18 49 0-0] 48 15-0|48 10-0} 113 48 28-3 || 43 30-0} 43 40-0| 43 25-0) 317 43 31-7|| 23 55 3-4 
Sept. 28 | 48 45-0| 48 10-0 | 48 25-0} 293 48 26-7 |) 43 50-0} 43 25-0| 43 10-0) 317 43 28-3|| 23 55 1-6 
Oct. 18 || 48 50-0) 48 15-0} 48 25-0} 293 48 30-0)| 43 55-0| 43 35-0) 42 55-0] 317 43 28-3] 23 54 58-3 
Noy. 2|| 48 50-0| 48 20-0} 48 15-0) 293 48 28-3]/ 43 50-0] 43 35-0) 42 55-0] 317 43 26-7) 23 54 58-4 
Noy. 23 || 46 50-0| 46 40-0| 46 25-0] 293 46 38-3]| 40 45-0) 41 50-0| 41 30-0} 317 41 21-7]] 23 54 43-4 
Dee. 3]| 48 15-0) 48 7-5| 47 55-0| 293 48 5-8]| 42 10-0] 43 10-0| 43 0-0] 317 42 46-7] 23 54 40-9 
The following mean values of Angle A were adopted :— 
August 7—November 23. 1841, Angle A=23° 54’ 57"-2. 
January 18, and February 1. 1842, .......... =23° 50’ 7-5. 
February 15—December 24. 1842, ......... =23° 50’ 19-3, 
‘The observation for the value of A, Dec. 23. 1841, has not been used in taking 
the mean for 1841. 
Between Dec. 3. 1841 and Jan. 13. 1842, the pillar of the reading telescope of 
the Declinometer was shifted. There is no register of the period at which this was 
done, but it is believed to have been at the same period at which the long scale 
was inserted in place of the short one on the Declination Magnet, or Dec. 28-9, 1841. 
The observations of Angle A, Jan. 18. and Feb. 1. 1842, have been separated 
from the others for that year, as they are considerably less, and the difference may 
have been due to some cause unrecorded. 
In the observations after July 13. 1842, the reading for each vernier is the 
mean of several made with different lights. The light was generally projected on 
the verniers in the direction of the divisions, by means of a mirror. 
The two observations, July 13. 1841 and the first on Aug. 16, were rejected 
in taking the mean, as they were noted as having been made with bad lights, when 
the coinciding divisions could not be well determined. Retaining the observation 
of Dec. 3. 1841, the mean value of Angle A for 1841=23° 54’ 55"2. Using the 
observations rejected in 1842, the mean value after Feb, 1842 = 23° 50’ 19-1’. 
MAG. AND MET. OBS, VOL. I. sf 
