OF THE ECLIPTIC. 199 



17. We now proceed to deduce the apparent obliquity of the ecliptic 



from what precedes. 



Zenith Distance, 21st of December, 1809, ............... 36 3\ 50.52 



21st of ftune, 1810...... :,.".-/./: 10 23 36.11 



Distance of Tropics,....!,.... ............... 46 55 26.53 



Half sum or apparent Obliquity............. 23 27 43.26 



Solar Nutation,*.. .................. ........ -j~ 51 



Obliquity for the middle of J 810,. ................... ......... 23 27 44.17 



Zeni(h Distance, 21st of June, 1810, 10 23 36.11 



. ___ 21st of December, 1810..................... 36 31 46.28 



Distance of Tropics, 46 55 22.39 



Half sum or apparent Obliquity............. 23 27 41.19 



Solar Nutation............... ........... -J- 51 



Obliquity for the beginning of 1811........................... 23 27 41.70 



Obliquity for July 1st, 1810, N. A........................... 23 27 42.12 



by Observation,.. .......................... ......... 23 27 44.17 



Difference, .................................. -f- 8.05 



Obliquity for January 1st, 181 1, N. A.... 23 27 41.48 



. by Observation, 23 27 42.10 



Difference, -}- 0.28 



/ 



* For the solar nutation we kave the following formula. Let the sun's longitude = L. 

 The solar precession = P. The obliquity of ecliptic = Obi. N = the nutation. Then, 



. Sin. Obi. P _. , _. 0.4341 



NssSin.* Lx- X - = Sin. r L x ~ X 3''.628=Sm. 2 Lx 1", nearly, 



90 4 1.570 



and when L = 90, then Sin. 2 = 1, and N = 1 nearly. Doctor Vince makes it 1 iu the win- 



ter, and 0.7 in the summer solstice, the mean of which is 51. 



