ON SOLAR PHYSICS. 
5 
Neglecting the effects of hourly motion and of error of perpendicularity to each other 
of the wires, we have from the geometry of the figure, if we call R and § respectively 
the sun’s radius and north polar distance, 
BC S I A I R 
2A B Sj S 3 15 . sin 8 . (A 2 — A t )’ 
AC S 2 B t R 
2 . A B S 2 S 4 15 . sin 8. (B 2 — Bj)’ 
whence 
or tan B AC = cot<p=^i£®i, 0 r tanft= ^~^| - 
The observations for the determination of <p are repeated at intervals of a few weeks ; 
and generally two sets of observations are taken, one on each side of the meridian. 
From the results and by interpolation the magnitude of <p is deduced for each sun-pic- 
ture taken. 
The following is an example of the observations : — 
August 25th, 1864. Sun East of Meridian. 
Kew Mean Time. 
First Observation. 
Second Observation. 
Third Observation. 
h m 
s 
b m 
s 
b 
m 
s 
10 12 
12-0 
10 16 
23-0 
10 
21 
31-5 
► 
12 
. 31-5 
16 
43-0 
21 
55-5 
l 2 
15 
14-5 
19 
25-5 
24 
35-0 
»2 
15 
34-0 
19 
45-5 
24 
58-5 
>- 2 — A, 
182-5 
182-5 
183-5 
’2— Bl 
182-5 
182-5 
183-0 
Mean A 2 — A t = 
=182-83 log =2-2620475 
B 2 — B,= 
=182-67 log =2-2616672 
-e 
II 
0"i 
o 
l'-5 log tan =0-0003803 
Sun West of Meridian. 
First Observation. Second Observation. 
Third Observation. 
Fourth Observation. 
b m 
s 
b m 
s 
b m 
s 
b m 
8 
2 58 
19-0 
3 2 
17-5 
3 6 
16-5 
3 10 
22-0 
58 
31-5 
2 
34-0 
- 6 
32-5 
10 
36-5 
3 1 
20-5 
5 
19-0 
1 9 
19-0 
13 
24-5 
1 
32-5 
5 
35-0 
9 
34-0 
13 
38-0 
1 
181-5 
181-5 
182-5 
182-5 
1 
181-0 
181-0 
181-5 
181-5 
Mean A 2 -A 1= zl82-00 log =2-2600714 
B.-B, =181-25 log =2-2582780 
<p=45° 7'T log tan =0-0017934 
