80 



mote, I find, by o25 observations of circumpolar stars, the 

 refraction at 45°, (Bar. 29, 60 inches and Therm. 50".) 



= 5?",42 . 



The same by the French Tables - - = 57,57 



The same resulting from the direct experiments 

 on the refractive force of air, applied to the 

 formula. - - = 57,67 



The quantity in the French tables was ascertained from 

 the resuhs ot the observations of M. M. Piazzi & Delambre, 

 applied to Laplace's formula by Delambre himself. 



My result from the number of observations, from the care 

 ■used in making them, and from the excellence of my instru- 

 ment, seems entitled to as much confidence as can be given 

 to a conclusion derived from observations of circumpolar 

 stars, and there is no difference worthy of notice between 

 my result and that of Delambre. But from the nature of the 

 direct experiments on the refractive force of air, the results 

 seem capable of greater exactness than can be derived from 

 observations of circuiri polar stars, and therefore strictly 

 perhaps ^ve ought to adopt the result so deduced. However 

 the quantity in the French tables is so nearly equal to this 

 that no inconvenience can arise in the nicest researches in 

 astronomy from adopting these tables. 



It is of much importance that the same tables of refraction 

 should be used by astronomers, and it will afford satisfaction 

 to the author of thjs paper, should it in any manner conduce 

 to this desirable end. It cannot be doubted but that sooner 

 or later the refractions as given by the French tables as far as 



