the rate of two in. per hour. 



The integration yielding the daily radiation 

 total was performed with a planimeter and day 

 length was computed from the Speedomax trace. 

 The value for the daily total is given, together 

 with other data, in the tables containing the 

 noon station observations. 



2. Submarine daylight 



Two different filters and submarine photometers 

 were utilized in the measurement of submarine 

 daylight. The transmission characteristics of 

 the two filters (Chance OB- 10 and Wratten No. 

 V?) are given in Figure 2. Since the trans- 

 mission of the Wratten 1+5 changed somewhat 

 during its use, a third curve is given which 

 was made with this filter immediately after the 

 return of the expedition. The darkening of 

 the 1+5 filter was assumed to be a gradual process 

 and, as there was no significant shift in the 

 spectral characteristics, all readings made 

 with this filter are believed to be comparable. 



Both of the photometers employed were essentially 

 identical, the only important difference being 

 that the collector plate (abraded translucent 

 plastic) in the first instrument (used from 

 Station S-l to S-1+) was elevated above the 

 instrument housing in such a manner that the 

 flat plate collector was not shadowed and had 

 an angle of acceptance of IflO" . In the second 

 instrument, used throughout the remainder of 

 the expedition, the angle of acceptance of 

 the collector was somewhat less than l8o° owing 

 to the fact that a shoulder on the photometer 

 housing rose a few millimeters above and around 

 the collector plate. 



With a single exception reducing screens were 

 not employed. The photometer was lowered in the 

 water until the output of the Photronic cell 

 (Weston 856, Type RR) in the photometer was 

 less than 1000 ua (usually at about 2 m. depth) . 

 The output of a gimbals-mounted deck cell, like- 

 wise filtered with a Wratten 1+5 filter, was not- 

 ed at the same moment as the output of the sub- 

 merged cell was recorded. This process was 

 repeated at successive depths until the output 



of the submarine cell was too low to be 

 measured with the microammeter . Due to 

 fluctuations in ambient light and distur- 

 bance caused by waves and swell, readings at 

 various depths were not made until an 

 apparent equilibrium had been reached. In 

 cases where wave action was particularly 

 disturbing and/or fluctuations in ambient 

 light were very marked, simultaneous readings 

 of the output of the deck and underwater cell 

 were repeated and an average of these values 

 was used. 



The current generated by the Photronic cell in 

 the photometer was measured with a damped 

 Rawson multimeter (0-50, 0-100, 0-200, 0-500, 

 0-1000 (ia) which possessed an internal 

 resistance (on all scales) of 100 ohms. The 

 output of the deck cell was measured with a 

 0-1 milliampere meter (internal resistance: 

 50 ohms ) . 



The data presented in the tables have been 

 corrected in the following manner: all 

 of the submarine photometric data (^a) have 

 been corrected for departures in linearity of 

 response of the photronic cell, and these 

 values in turn adjusted to a constant but 

 arbitrary incident radiation value (deck 

 cell reading) . The "true" instrument depth 

 has likewise been computed from wire-angle 

 measurements and length of wire out. 



The diffuse attenuation coefficient per unit 

 distance (meter), k, and the percent trans- 

 mission per unit distance (meter), T, have 

 been calculated for each depth interval using 

 the following formulas: 



In I 



AZ, 



- In I 



AZ, 



- Z, 





where I is the corrected output of the 

 submerged cell, Z is the depth in meters, 

 and refers to the spectral sensitivity of 

 the Photronic cell-color filter combination 

 employed (see Figure 2). 



3. Salinity, temperature, depth 



