Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/12

12 Experiment II.--Sunlight, June, 1890, midday. Length of cell (inside measures), 3 inches; breadth, 2.1 inches.

When light passed through length 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 67º.

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. Mean reading. Mean reading. Mean reading Cells. Value. Value. Value. White = 78. White = 100. White = 78. White = 100. White = 78. White = 100. 23:5 3 in., clear 3 in., turbid 70 55 89.5 70-5 21 39 68 51 87 65.5 49 32 63 41 46 85 1st Exposure action through clear water action through turbid water 21 = 538. 39 2nd 23.5 = '534. 14 3rd 46 = 541. 85 Mean = 538.

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 M= 3 .98954 = 330. 3 1st exposure. 2nd exposure. 3rd exposure. Mean reading. Mean reading Mean reading. Cell. Value. Value. Value. White White = 78. White = 78. White = 100. White = 78. White = 100. = 100. 2:1 in., clear 21 in., turbid 57 48 73 61.5 36 48 41 32 52.5 41 62 85 27 20 34.5 26 106 140