117 



But from the circumstances of the case there seems to be 

 no reason lo expect any exact and convenient method of de- 

 termining the quantity of refraction for low altitudes. 



It is not likely the irregularities will be ever submitted to 

 any law, and investigations respecting formulce for refractions 

 for zenith distances greater than about 80° may be considered 

 more curious than useful. For less zenith distances, the 

 French tables, as it has been a principal object of this paper 

 to shew, seem as accurate as can be desired. 



