PRISMATIC CAAIERAS DURING THE TOTAL ECLIPSE OF THE SUN. 715 
(2.) Brazilian Observations. 
The prismatic camera employed in Brazil was one of 3 inches aperture. The light 
from the sun was reflected on to the prisms from the mirror of a siderostat. The 
object glass was a Dallmeyer doublet of 19 inches equivalent focal length ; the image 
of the inner corona, therefore, is a ring of 0‘2 inch diameter. 
Before the doublet were placed two prisms of 3 inches clear aperture, with their 
refracting edges perpendicular to the horizontal, each having a refractive angle of 60°. 
The length of the spectrum given by this combination was 1*65 inches from F to K, 
or 2‘5 inches from Dg to K. Three specially constructed dark slides, carrying eight 
plates each (4;^ in. X If in.), were employed, the change from plate to plate being 
effected by means of a rack and pinion attached to the dark slides. A complete list 
of the photographs taken is given in the following table :— 
Table of Exposures. 
. 
No. 
Kind of plate. 
Exposure. 
Interval 
of change. 
Remarks. 
I 
Mawson. 
Inst. 
14 mins. 
Abont 14 mins, befor’e totality. 
2 
2 secs. 
2 .secs. 
Commencement of totality. 
O 
• } 
. 
8 „ 
2 
" 51 
4 
„ (Stellai’) 
Inst. 
2 „ 
5 
?? ... 
55 
2 „ 
6 
5 secs. 
2 „ 
7 
?? . 
30 „ 
0 
" 55 
8 
. 
15 ,, 
8 „ 
9 
„ (Stellar) 
Inst. 
2 „ 
10 
I.socliromatic (Edwards’) . 
5 secs. 
2 „ 
11 
30 „ 
2 
12 
60 „ 
2 „ 
Aliddle of eclipse. 
13 
•1 *1 • 
lust. 
0 
^ 5 5 
14 
30 secs. 
2 „ 
15 
5 „ 
0 
55 
16 
Mawson. 
30 „ 
10 „ 
17 
15 „ 
2 „ 
18 
,, (Stellar) 
Inst. 
0 
^ 55 
Last photo in totality. 
19 
. 
5 secs. 
o 
5 1 
After totality. 
20 
51 r- .... 
Inst. 
5 „ 
5 5 55 
21 
10 „ 
55 5 5 ! 
22 
8 secs. 
20 „ 
55 55 ; 
23 
Inst. 
2 
55 55 1 
: 24 
^ 5? . 
55 
5^ 55 
The exposures were made by means of a shutter, which could be closed and opened 
from the camera end with a cord; when this was done as rapidly as possible the 
exposure is tabulated as instantaneous. 
The sun was observed through a finder fixed on the camera, until it was seen that 
totality was very near commencement. The exposures were then begun. 
4 Y 2 
