104 



The Co-latitude of the Observatory of Trinity College, Dublin, 

 deduced from Observations of Circumpolar Stars, by different 

 Tables of Refraction.— Observed Refractions of Capella^ be- 

 low the Pole. 



14. Comparisons of the Co-latitude as determined by stars 

 near to, and remote from the pole, serve for a criterion of 

 the accuracy of the tables of refraction used. 



In the following table the co-latitude is determined by 

 four different methods of computing the refraction. 



1. In column A, by the formula 56", 9 tan. (^— 3, 2 ref.) 



bar. 500 



^ 29,6 ^ ^50 + therm. ' 



2. In column B, by the formula d&',9 tan. (^—3 ref.) >; 



bar. 400 



29,6 350 + therm. 



3. In column C, by the preceding tables, which give the 

 same results as the French tables. 



4. In column D, by the value of "^ = 57",82 as de- 



' •' sin. 1 



duced from experiment. 



The second formula is Bradley's. 



The first formula is what appeared to me by my observa- 

 tions in 1 809, to give the refraction at low altitudes more ex- 

 actly than Bradley's formula, and also to give the effects of 

 the changes of temperature more exactly. 



