432 



Talbot H. Waterman 



In general the e vector of the polarization was horizontal in the sun's and the anti- 

 sun's bearings but was tilted towards the sun at azimuths normal to these lines of 

 sight. When the polarization plane appeared to be tilted in bearings towards or away 

 from the sun, it has been assumed that this was the result of the camera not being 

 precisely horizontal or pointing accurately along the ship's heading as discussed under 

 procedure. The magnitude of these influences, obvious in the directions cited, should 

 in addition give some information on the reliability of the measurements made normal 

 to the sun's azimuth where the present data do not otherwise provide any estimate of 

 variance. 



The tables and photographs illustrate two important points inherent in the total 

 data. First is that the sun's position influenced the pattern of submarine polarization 

 at all depths so far studied, including 200 m, the deepest of the present stations, and 

 the shallow water observations made previously. The optical effects involved here 

 were (1) the angle of refraction of the incident rays of sunlight and (2) the apparent 

 origin of underwater polarization from primary Rayleigh scattering of directional 

 light beams, which causes the polarization plane to be normal to the angle of 

 refraction. 



Station No. 11 



Sun's altitude: 51° 40' 



Angle of sunlight incidence: 38° 



Depth of measurements : 200 m 



Table II 

 13°07'N, 59°53'W. 



Dec. 2, 1954 



Sun's azimuth: 201° 



Calculated angle of refraction: 27^ 



Depth to bottom: 



This effect was certainly predominant in shallow water. It was also at the 30 m 

 station (No. 8) in the present series (Fig. 2). Here the tilt of the polarization plane 

 averaged 43° for lines of sight normal to the sun's bearing. This angle was almost 

 identical with the corresponding angle of refraction (42°) calculated from the observed 

 solar altitude, assuming a refractive index for the water of 1 -34. 



Such an effect of the sun's altitude, and hence the angle of refraction of sunlight 

 entering the water, must also be involved in the plane of polarization at greater 

 depths, too. Yet the present data do not afford much direct evidence for this since 

 repeated measurements were not made systematically at the same depth with different 

 solar altitudes. However, in the single satisfactory case where such a comparison can 

 be made, strong support for this generalization is found. This comes from the data of 

 stations 7 and 10, both at 150 m. 



Here the angles of refraction of sunlight, computed from the sun's elevations, were 

 not the same because of the different times of day when the two sets of photographs 

 were made. It will be seen in Table III that the deviations of the polarization planes 



