12 
CAPTAIN W. DE W. ABNEY ON THE TRANSMISSION 
Experiment II. —Sunlight, June, 1890, midday. Length of cell (inside measures), 
8 inches ; breadth, 2‘1 inches. 
When light passed through ksngth of cell to the sensitive paper a double sector, 
with an opening 36°, rotated in front of clear cell. 
When light passed through the breadth, the sector opening was 67°. 
Thus, with cells placed lengthways, the value obtained had to be multiplied by 
180°/36°= 5. When the cells were placed breadthways, the light passing through 
the clear cell had to be multiplied by 180/67 = 2‘686. 
1st exposure. 
2nd exposure. 
3rd exposure. t 
; 
Mean reading. 
Mean reading. 
Mean reading. 
1 
1 
Cells. 
\ 
Value. 
Value. 
Value. 
White 
White 
White 
White 
White 
White 
= 78. 
= 100. 
= 78. 
= 100. 
= 78. 
= 100. 
.3 in., clear 
70 
89-5 
21 
68 
87 
23-5 
49 
63 
46 
3 in., turbid . 
55 
70’5 
39 
51 
65-5 
44 
32 
41 
85 1 
i 
. „ action tlirougli clear water 21 
St Exposure j^gtion through turbid water “ 39 
2 nd 
3rd 
23-5 
44 
- ^ 
- 85 
Mean = '538, 
•538. 
•534. 
•541. 
Photographic light passing through the clear water — •538 X 5 = 2^69 times that 
passing through the turbid cell. 
Using the formula as before, 
log 2-69 -98954 
Pi = —X— = -X— = *330. 
o o 
1st exposur 
e. 
2nd exposure. 
3rd exjiosui’e. 
Cell. 
Mean r 
eading. 
Mean r 
eading. 
Mean r 
eading. 
Value. 
V alue. 
Value. 
White 
White 
White 
White 
White 
White 
= 78. 
= 100. 
= 78. 
= 100. 
= 78. 
= 100. 
21 in., clear 
57 
73 
36 
41 
52-5 
62 
27 
34-5 
106 
2 1 in., turbid . 
1 
48 
61-5 
48 
32 
41 
85 
20 
26 
140 
