194 
SIR NORMAX LOCKYER AXD OTHERS OX THE 
comparatively long ones. A layer 10 inches in depth, for example, would be exposed 
over a length of 112° at the instant of contact, and a layer 1 inch in depth over a 
length of 34°. 
Calculations showed that, after reflection from the mirror of a siderostat along a 
horizontal meridian line, the north point of the sun’s axis, as seen by an observer 
looking into the mirror, would be 7° 1 3' to the left of the top of the image ; the 
east and west points were to the right and left respectively. 
It was evident then that with dispersion in a horizontal direction there would 
be a little overlapping of adjacent chromospheric arcs, but still it was considered 
desirable that in one of the instruments at least the dispersion should be arranged 
so as to give the arcs quite symmeti'ical. 
Photographs taken with the %-inch Prismatic Cctmera. 
Mr. Fowler’s progi-amme was to begin taking a series of ten snapshot pictures 
5 seconds before the commencement of totality, to obtain a record every second or 
thereabouts of the spectrum of the chromosphere. After this he exposed eight 
other plates to secure photographs of the coronal rings, the exposures being of various 
lengths. It was also arranged that at 5 seconds before the eiid of totality he 
should commence another series of ten snapshots, exposing the last of these some 
few seconds after totality. The actual times of exposure, kc., ai'e shown in the 
following table :— 
Table of Exposures for G-inch Pilsmatic Camera. 
Xumher. 
Kind of plate. 
G.M.T. of expo¬ 
sure, A.M. 
Exposure. 
Remarks. 
]i. in 
S. 
1. 
Edwards’ snapshot, isochromatic 
7 52 
35 
Inst. 
h 
'I’l 1' 
36 
11 
1 ^ 1' 
37 
11 
d 
11 11 
38 
,, 
e 
11 1« 11 
40 
f 
11 1 • 11 
41 
1) 
Beginning of totality. 
!l 
11 1' 1* 
42 
i> 
h 
11 11 11 
43 
11 
Ic 
11 1' 
45 
11 
■ 1 
>1 11 11 
46 
11 
2. a 
Edwards’ snapshot, isochromatic 
r 7 52 
1 to 53 
50 
40 
j> 50 secs. 
Slide changed. 
h 
11 11 1* 
7 53 
41 
Inst. 
c 
r 7 53 
44 
j> 6 sees. 
11 11 11 
|to 
50 
d 
•1 11 11 
7 53 
51 
Inst. 
