518 ACCOUNT OF ASTRONOMICAL OBSERVATIONS 



will fall short 6f the differences of declinations E D, 

 and E dhyxhQ small are LL 



1 3. Let now the zenith be altered into ^ (Fig 2) so 

 that d be now north of it, and let ^ be the place of a 

 third star, south of the zenith C,. Then if wc use the 

 declination of d (which before gave us too low a lati- 

 tude) it will now give it in x ; and if we use that of <^ it 

 will fall in ^\ south of the true zenith : so that instead 

 of having E D — E 'Jr=sum of the four zenith distances, 

 we have it (Fig. 1) — D L \-Ll ■\-ld + ^A-f ^ A + A '^* 

 That is, the four observed distances -f- the small arcs 

 L I -l-A A* Therefore, if we suppose the declination E 

 D to have been well determined, that of Jia too low by 

 the arc L /, and that of <^\ by LI j^\ a* 



14. For example ; let the true place of Aldeharan 

 be at A', and its apparent place (affected by the error in 

 the declination) be at Z), ReguJus at d and » Ononis at 

 ', then at the observations at Paudree and Tiivanda- 

 foram we have 



D L 20 46' 33'' .682 NO 



Id O 24 43 .040 S. \ 



dx 1 10 9 .920 N. f 



A ^Y 4 23 4 .810 S.J 



id O 24 43 .040 S. I q£ ^jjg g^^-^g zeniths. 



dx 1 10 9 .920 N. I ^ 



Sum, 8 44 31 .452 

 Now the mean declination oi Aldeharan being 

 Equal . . . l6« 6' 23" -73 

 And a Orionis = 7 21 36 .61 



WehaveED— ii:u^8 44 47 .12 

 8 44 31 .45 



Diff. i./ + ^ A= ' • 15 .55 



