of an atmosphere nearly resembling that of the earth. 161 
and at the horizon, when v = o, 
r= . 17972 ( . 09214 66 — . 10367 h 1 7-7 — -) = 
. 009840 = 3S' 42",5 ; which is only i",5 less than the quan- 
tity assigned by the French tables and in the Nautical Alma- 
nac, while Mr. Ivory makes it 34' 17", 5. Again, if we take 
v = . 1, for the altitude 5 0 44' 21", we obtain 8' 49", 5 for the re- 
fraction, while the Nautical Almanac gives us 8 ' 53", and Mr. 
Ivory’s table 8 ' 49 ",6. There is however no reason for pro- 
ceeding to compute a new table by this formula, the method 
employed for the table in the Nautical Almanac being rather 
more compendious in all common cases : and even if it were 
desired to represent Mr. Ivory’s table by the approxima- 
tion there employed, we might obtain the same results, with 
an error never much exceeding a single second, from the 
equation v ,• 
. 00028333 = T r + r 2 + 54 oo ~{ T r+ r 9 
Welbeck Street , 
3rd. February , 1824. 
MDCCCXXIV. 
Y 
