101 



Zenith 

 distance. 



45 

 50 

 60 



70 



74 



Refraction 

 deduced 

 from the . 

 experiment. 



57.7 

 08,7 

 99,7 



157,3 

 198,6 



Refraction by 



the French 



Tables. 



57^6 

 68,6 

 99,4 



157,0 

 198,2 



.y\ 



Therefore, as it is of considerable importance, particularly 

 with a view of comparing observations made in different 

 places, that the same refractions should be generally used, 

 no objection, I apprehend, can be made to the general 

 adoption as far as about 80° of the French refractions which 

 are now so well known, 



13. Perhaps the following tables deduced from the above 

 formula, may be considered rather more convenient in many 

 instances than the French tables; they will certainly furnish 

 a useful check. The advantage they afford is derived from 

 the faciiity with which the computation can be made by help 

 of tables of logarithms and of logarithmic tangents to four or 

 five places of figures, such as are in the " tables requisite to 

 be used with the nautical ephemeris." By these the log. tan- 

 i>ent of the zenith distance can be taken out at once, and the 

 inconvenience of proportioning for the minutes of zenith dis- 

 tance avoided, which is greater than the new inconvenience 

 occasioned by the second table. Hence the tables here given 



