40G On the ulmosphericul Refraction. 



tion of the atmosphere : for, I find that the refractions at the 

 horizon depend not onlv upon the initial rate of the decrease of 

 heat, but also, although in a verv small degree, upon the acce- 

 leration. 



Since my last communication, I have applied to mv method 

 an artifice similar to that employed by Laplace for integrating 

 the expression of the refraction near the horizon. The result is 

 contained in the following formula, the letters denoting the same 

 things as before : 



Log. tan f = 19-0217998— log. cos. A ; then, 



Log. of Coefficients. 



R = sin x/ll09"-26 tan \ (^ .. 



665-55 tan'i (p .... 2-8231838 

 221-85 tan'- I ^ .... 23460625 

 31-69 tan- \ <^ .... 1-5009645. 



Owing to the artifice employed in the integration, this formula 

 is a finite expression. It supposes an atmosphere similar to that 

 of Laplace ; that is, one in which the initial rate of the decrease 

 of heat is too great, but continuJiUy becoming less and less as 

 the elevation increases. It is reduced to the same state of the 

 barometer and thermometer as in the French Tables. To the 

 extent of 85° from the zenith, it does not differ sensibly from 

 those Tables, nor from the former formula : for less altitudes it 

 comes a little nearer the Tables, as is shown below. 



3-0450325 



i have the honour to be, &;c. 



June 6, 1821. 



J. Ivory. 



LXXIl. True apparent Right Ascension of Dr. 

 36 Stars for every Day in the Year 1821. 

 J. Groody. 



[Continued from p. o55.] 



Maskklyne's 

 By the Rev. 



1S21. 



