OF SUNLIGHT THROUGH THE EARTH’S ATMOSPHERE. 
13 
„ action through clear water 
1st Exposure through turbid wsier 
2 nd 
3rd 
48 
85 
140 
106 
•750. 
•729. 
•757. 
Mean = ^74 5. 
Photographic light passing through clear water = ^745 X 2^686 = 2^00 times that 
passing through turbid water. 
Using formula as before, 
log 2-00 -69315 
= ^ = — =-330. 
Mean of /x^ = -330. 
The optical measures of the clear and turbid cells in the direction of tlie length 
were— 
3 in., clear water, 36^5 ; turbid water, 26. 
Clear water 
Using same formula 
Turbid 
lo" 1-4 -33647 
= 1-4. 
[X = 
= • 1121 , 
The mean value of is •SSO, and as 
therefore 
= ^ X 105, 
A -330 
X 105 = 309-1. 
Experiment III .—Arc electric light; light from crater of positive pole alone used 
—the arc being cut off by screens. 
Length of cell, inside measure, 3 inches; breadth, 1-7 inch. When light passed 
through length of cells a double sector of 16^° rotated in front ot the cell containing 
clear water. When passed through the breadth of the cell 28“. 
For the cells placed lengthways the value of the light passing through the clear 
cell had to be multiplied by 180/16-5 = 10'91, when placed breadthways 180/28 = 6-43 
