150 I. P. Косн. 
In Fig. 10 the sights OX and IK (small instrument—Cross) have 
been revolved upon the vertical plane containing OI. 
The sight from O to 
X is to be carried to 
point P, situated in 
the vertical ХО and 
on the line OI. Ina 
corresponding manner 
the sight from I to K is 
to be carried to point E 
Fig. 10. in the vertical KS. 
Known beforehand: 
The zenith distance of X from O 86°50'15"; further 
ХО = 69 ‘cos 415597 2326 11: 
IQ = XD (Fig. 9) = 3.25m.| 
OS = ОЕ (Fig. 9) = 9.72 m. J 
he — Ри, 
ЕВ — 285 < 97725131 3:09 — 2,3] m: 
EX — 326 32> Fans 09 — 3.0m: 
(approximation) 
After this we get the corrections of the zenith distances measured 
from Г to К. 
2 31 
3 CUT. HAITI VERS AT UU 
from О to X. 
3.08 DR 
A Le == + © 71945 = + 1'24 8. 
In the zenith distances given in the following between the Ob- 
servatory and Cairn X these corrections are applied. 
In order to be able to compute the co-efficient of refraction we 
must finally know the radius of curvature R. 
1 1 1 
We ee 2 = Amen: 
We get R м °° a+ ху sin a 
where M and N are the radii of curvature of the meridian and its 
normal segment, and where a is the azimuth of the segment in 
question. In the case of the ensuing computation it has, however, 
not been necessary to make allowance for the azimuth; it has been 
sufficient to put В = VMN and from this to compute В for the 
latitude of the Observatory. By interpolating in the tables of log, 
and log 5 p. 235 we get 
ee = 1:49150. 
ow 
