DETERMINATION OF DEFLECTION OF LIGHT BY THE SUN’S GRAVITATIONAL FIELD. 301 
G.M.T. 
Ther. 
G.M.T. 
Ther. 
G.M.T. 
Ther. 
G.M.T. 
Ther. 
d. h. m. 
28 22 45 
23 0 
15 
0 
82-4 
84-2 
82-4 
d. h. m. 
28 23 30 
45 
29 0 0 
O 
80-6 
82-4 
80-6 
d. h. m. 
29 0 15 
30 
45 
O 
82-0 
82- 4 
83- 1 
d. h. m. 
29 1 0 
15 
30 
O 
83- 8 
84- 2 
84-2 
15. On June 7, having completed the development, we left Sobral for Fortaleza, 
retmming on July 9 for the purpose of securing comparison plates of the eclipse field. 
Before our departure we dismounted the mirrors and driving clocks which were brought 
into the house to avoid the exposure to dust. The telescopes and coelostats were left 
in situ. Before removing the mirrors we marked their positions in their cells so that 
they could be replaced in exactly the same position. 
After our return to Sobral the mirrors and clocks were remounted ; the photography 
of the eclipse field was commenced on the morning of July 11 (civil). The difficulty of 
finding the field with the coelostats was overcome by making a rough hour circle on the 
heads of the coelostats out of millimetre paper. 
The following is the list of exposures made on the field for comparison with the eclipse 
photographs :— 
Astrograjrhic Telescope. 
4-inch Telescope. 
Ref. 
No. 
Date. 
G.M.T. 
No. of 
expo¬ 
sures. 
Dura¬ 
tion. 
Altitude. 
Ref. 
No. 
Dsite. 
G.M.T. 
No. of 
expo¬ 
sures. 
Dura¬ 
tion. 
Altitude. 
h. m. 
s. 
0 
Ill 
July 10 
20 5 
3 
5 
28-9 
II 2 
20 16 
2 
5 
3M 
h. m. 
s. 
0 
II 3 
20 21 
1 
5 
32-2 
14i 
July 13 
20 7 
2 
25 
32-4 
14i 
July 13 
20 13 
3 
5 
33-7 
lb 
20 16 
2 
20 
34-3 
1^2 
20 17 
2 
5 
34-5 
1^3 
20 19 
2 
5 
34-9 
15j 
July 14 
20 17 
2 
20 
35-4 
15i 
July 14 
20 15 
3 
5 
34-9 
152 
20 22 
2 
20 
36-4 
152 
20 20 
2 
5 
36-1 
153 
20 23 
2 
5 
36-6 
lb 
July 16 
20 6 
3 
15 
34-7 
lb 
July 16 
20 2 
4 
3 
33-8 
lb 
20 24 
2 
15 
38-6 
lb 
20 15 
3 
3 
36-6 
lb 
20 23 
2 
3 
38-3 
lb 
20 25 
2 
5 
38-8 
18/ 
July 17 
19 57 
3 
20 
33-6 
181 
July 17 
19 50 
3 
4 
32-8 
I 82 
20 24 
2 
20 
39-2 
183 
20 1 
2 
4 
34-4 
183 
20 20 
3 
4 
38-6 
184 
20 25 
2 
3 
39-5 
The reference numbers follow the civil dates. 
* The 4-inch plate, No. 18i, was taken through the glass (see § 17, injra) to facilitate the measurement, 
and is referred to as the scale plate. 
2 T 2 
