242 Mr. Galbraith's further Observations on the 



The error arising from the use of Bradley's refractions would 

 produce 1"*22 more, or 2"-22 in all. Now in the Greenwich 

 Observations for January &c. 1827, page 13 of deductions, 

 the mean of 15 determinations from 1812 till 1826, and re- 

 duced to 1820, gives 



Summer obliquity reduced 23° 27' 46"-76 



Winter obliquity 23 27 44 '39 



Difference from actual results 2 *37 



Predicted difference 2 '22 



nearly the same, the error being only — 0'.'*15. 



Now this conclusion, agreeing so nearly with our previous 

 results, seems almost decisive of the question. There can be 

 little doubt that the discordances between the observed ob- 

 liquity at the summer and winter solstices are attributable, al- 

 most entirely, to an erroneous table of refractions for deter- 

 mining both the latitude and the obliquity. 



To deduce the true mean obliquity from those recorded in 

 the Greenwich Observations of 1827, it will be necessary to 

 apply the small corrections which have been just pointed out. 



Mean obliquity, summer 23° 27' 46"*76, winter 23° 27' 44"-39 



Errors in Bradley's refr. + -34 + 1 '56 



Error in latitude — -50 + '50 



Correct mean obliquity 23 27 46 -60 23 27 46 -45 



The accordance between the results is now apparent; and 

 it is not brought about by design, but by detailing fully the 

 principles upon which it has been obtained. Had the lati- 

 tude been 51° 28' 38"*4, — that which I deduced from Ivory's 

 refractions, (which, so far as I have been able to judge from 

 what comparisons I have made, are among the most accurate 

 tables of refractions now to be found,) — the accordance would 

 have been still closer, the summer coming out 23° 27' 46"*50, 

 and the winter 23° 27' 46"*55, the mean being the same in 

 both cases, or 23° 27' 46"*525. This result has been derived 

 from numerous observations on different years, reduced to 

 1820, and by that means may be presumed to be very cor- 

 rect. 



It may now be proper to deduce the annual diminution in 

 the same manner. 



The mean obliquity from the observations of Bradley, 

 Mayer, and Lacaille in 1750, was found to be 23° 28' 18"*33 



Sun's latitude with a contrary sign , 



Error in Bradley's refr. at summer solstice 



Error in Bradley's latitude of Greenwich 



Correct mean obliquity in January 1750 . 



+ 









•11 



+ 









•34 



— 





1 



•00 



23 



28 



17 



•78 







This 



