Introduction. 



XXI 













Table 7.— 



-Determinatic 



)ns of the Values of Angle A. 













Readings of Horizontal Circle 









For Declination Telescope. 





For North Mark. 



Date 









1 







1 



Angle A. 







Verniers. 







Verniers. 















1 



AT pa ji 









Mean. 









- 



V. 



B. 



C. 





A. 



B. 



C. 





1841. 





'/ 



' 



" 



' // 



o . 



' 



" 



'■ // 



' 



" 



o . „ 



o , 



Aug. 



7 



55 



10-0 



54 



150 



54 400 



233 54 41-7 



49 



150 



49 55-0 



49 



300 



77 49 33-7 



23 54 520 



Sept. 



4 



44 



50-0' 



45 



20-0 



44 50.0 



233 45 00 



40 



50 



40 5-0 



40 



0-0 



77 40 3-3 



23 55 3-3 



Sept. 



18 



49 



00 



48 



150 



-i8 100 



113 48 28-3 



43 



30-0 



43 40-0 



43 



250 



317 43 31-7 



23 55 3-4 



Sept. 



28 



48 



45-0 



48 



10-0 



48 250 



293 48 26-7 



43 



50-0 



43 250 



43 



100 



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 



Nov. 



2 



48 



500 



48 



20-0 



48 150 



293 48 28-3 



43 



500 



43 35-0 



42 



55-0 



317 43 26-7 



23 54 58-4 



Nov. 



2.3 



46 



50-0 



46 



400 



46 25-0 



293 46 38-3 



40 



45-0 



41 50-0 



41 



300 



317 41 21-7 



23 54 43-4 



Dec. 



.3 



48 



15-0 



48 



7-5 



47 550 



293 48 5-8 



42 



10-0 



43 100 



43 



00 



317 42 46-7 



23 54 40-9 



1842. 





























Jan. 



18 



50 



15-0 



50 



0-0 



49 500 



293 50 1-7 



40 



300 



40 15-0 



39 



40-0 



317 40 S-3 



23 50 6-6 



Feb. 



1 



52 



20-0 



51 



50-0 



52 350 



293 52 15-0 



42 



50-0 



42 30-0 



41 



50-0 



317 42 23-3 



23 50 8-3 



Feb. 



15 



49 



12-5 



48 



50-0 



49 50 



293 49 2-5 



39 



500 



39 22-5 



39 



10-0 



317 39 27-5 



23 50 25-0 



Feb. 



28 



48 



55-0 



48 



45-0 



48 40-0 



293 48 50-0 



39 



30-0 



39 5-0 



38 



40-0 



317 39 5-0 



23 50 15-0 



Mar. 



12 



49 



30-0 



49 



100 



49 25-0 



293 49 21-7 



40 



10-0 



39 50-0 



39 



10-0 



317 39 43-3 



23 50 21-6 



Mar. 



26 



49 



10-0 



48 



55-0 



49 100 



293 49 5-0 



39 



50-0 



39 35-0 



38 



500 



317 39 25-0 



23 50 20.0 



Apr. 



9 



49 



25-0 



49 



100 



49 300 



293 49 21-7 



40 



10-0 



39 45-0 



39 



15-0 



317 39 43-3 



23 50 21-6 



Apr. 



27 



52 



250 



52 



50 



52 400 



293 52 23-3 



43 



0-0 



42 52-5 



42 



100 



317 42 40-8 



23 50 17-5 



July 



13 



52 



40-0 



52 



45-0 



53 40-0 



233 53 1-7 



43 



30-0 



42 50-0 



43 



7-0 



77 43 9-0 



23 50 7-3 



July 



13 



52 



40-0 



52 



300 



53 200 



233 52 500 



43 



200 



42 50-0 



42 



55-0 



77 43 1-7 



23 50 9-5 



Aug. 



16 



52 



40-0 



52 



25-0 



53 6-6 



233 52 43-9 



43 



12-5 



42 52-5 



43 



8-0 



77 43 4-3 



23 50 20-4 



Aug. 



16 



52 



400 



52 



420 



53 100 



233 52 50-7 



42 



12-0 



42 550 



43 



10-0 



77 43 5-7 



23 50 17-7 



Sept. 



17 



52 



45-0 



53 



12-5 



52 42-5 



233 52 550 



43 



25.0 



43 0-0 



43 



10-0 



77 43 U-7 



23 50 16-7 



Oct. 



31 



52 



20-0 



. 52 



11-0 



52 50-0 



233 52 27-0 



42 



49-0 



42 37-5 



42 



40-0 



77 42 42-2 



23 50 15-2 



Oct. 



31 



52 



90 



! 52 



2-5 



52 450 



233 52 18-8 



42 



41-5 



42 27-5 



42 



39-0 



77 42 36-0 



23 50 16-2 



Dec. 



24 



52 



100 52 



16-5 



52 52-5 



233 52 26-3 



43 



5-0 



42 42-5 



42 



37-5 



77 42 48-3 



23 50 22-0 



taking 



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 

 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' 5o"-2. Using the 

 observations rejected in 1842, the mean value after Feb. 1842 — 23° 50' 19*1'''. 



MAG. AND MET. OBS. VOL. I. / 



