. Neglecting again n in the denominator, we have: 
(n, - ny) = T ctn (2), (119) 
or with (111), 
  
Q ; 
a-1l &-l 
T=-—— ten (2), A - T ) (120) 
o 
and with the notation of formula (115), 
a-l a-1 : : 
T" = À tan (3), (an - T ) | (121) 
The refraction for an aerial observer follows, from (116): 
u a-l | \ 
a = A tan (2), 5. om (122) 
a(T,-T ) p 
As mentioned on page 64, « becomes astronomical refraction (A,) for &ll points 
Outside the effective atmosphere for which To = 0. Consequently (121) reduces 
for T = 0 to: 
p 
  
A% = À tan (z), 7l (125) 
Introducing (125) into (115) we obtain: 
A D 
At = Al > À tan (2) + (124) 
& & 
a(T -T ) 
a p 
: qa. 7° 
"oo AM - 8 p 
As BAM 11 - (125). 
ar him -p 
a a p 
whereby for precision WOrk M^, can be computed from (9T). 
Refraction can now be taken into consideration by computing either A or 
(z - A) as required in formula (90). 
68 
mum C ERE 
ms! : EN