THE 



PHILOSOPHICAL MAGAZINE 



AND 



ANNALS OF PHILOSOPHY. 



[NEW SERIES.] 



OCTOBER 1830. 



XXXVIII. Further Observations on the Obliquity of the 

 Ecliptic. By William Galbraith, Esq. M.A. 



To the Editors of the Philosophical Magazine and Annals. 



Gentlemen, 



T N my paper published in the Phil. Mag. for July last, I en- 

 ■*• deavoured to show that the difference of the values of the 

 obliquity of the ecliptic, derived from observations made at the 

 summer and winter solstices, arose almost entirely from a small 

 error in the latitude and in the tables of refraction employed 

 in reducing the observations. The conclusion accorded well 

 with the observations made at Greenwich, and published in 

 Dr. Pearson's "Astronomy" till about the year 1820. Since 

 that time, however, the subjects of the latitude and obliquity 

 have been again discussed in the Greenwich Observations for 

 1826 and 1827. I have already shown that from the former 

 the latitude should be 51° 28' 38"*5 N., which is confirmed by 

 Bessel. From some observations which I reduced by means 

 of Ivory's refractions some years ago, it came out to be 51° 28' 

 38'H N. It appears that Mr. Pond prefers the use of Bradley's 

 refractions in reducing his observations ; and consequently all 

 his deductions must partake of the slight error attending the 

 application of these refractions. He therefore makes the co- 

 latitude of Greenwich 38° 31' 21", and the latitude51° 28' 39"N. 

 being that derived by Bradley's refractions from the Obser- 

 vations of 1826, page 4« of the results from October, Novem- 

 ber, &c. 



This result is half a second more than what I have adopted 

 as the correct one from our best tables of refractions, and would 

 produce a difference of 1" between the summer and winter 

 obliquities. 



N.S. Vol. 8. No. 46. Oct. 1830. 2 I The 



