VIII. ATMOSPHERIC CONDUCTIVITY RESULTS 

 EXPLANATORY NOTES AND COMMENTS 



Section vni is the fourth and last of the major tables 

 of data and contains hourly mean values, on Greenwich 

 Mean Time, of the electrical conductivity of the atmos- 

 phere in 10"4 esu. These values were obtained from 

 photographic records made with the recording apparatus 

 installed at San Francisco inAugust 1929. The recording 

 apparatus replaced the eye-reading electrometer with 

 which conductivity values given in the tables in sections 

 V and VI were obtained; other parts of the conductivity 

 equipment, including the air-flow system, air-flow fan, 

 and the central collecting cylinder, were retained with- 

 out change as they had been installed at the beginning of 

 the cruise. 



Between September 3 and November 18, 1929, the 

 ship was at sea sixty-eight days. During this time fifty- 

 eight complete days of record of conductivity were 

 obtained and seven days of partial record. Positive con- 

 ductivity was measured on thirty of the fifty-eight com- 

 plete days, and negative on the remaining twenty-eight. 

 The high percentage of complete days obtained during 

 the period of recording was very gratifying, indicating 

 that apparatus suitably designed and built for conditions 

 at sea can be maintained almost continuously in satis- 

 factory operation. 



Interpolated Values. --Interpolated hourly values 

 have been placed in brackets in the present table. "These 

 are almost all found in September, the first month of 

 recorder operation, when time devoted to calibration of 

 the apparatus was more lengthy than later, and when it 



was customary to shut down the apparatus because the 

 air -flow fan was turned off during magnetic observations. 

 In subsequent months calibration periods were so brief 

 as to obviate interpolation, and the shutting down for 

 magnetic work was discontinued as the running motor 

 was found to have no effect on the magnetic instruments. 

 In this table, as for the potential-gradient tabulation, in- 

 terpolation has been performed only for hours which 

 were quiet and undisturbed. 



Mean Daily Values. --AH the complete days have 

 been provided with daily mean values. Not all these days 

 were regarded as undisturbed, there being twenty-one 

 on which disturbed periods of a few hours were noted. 

 Under the column headed "disturbed hours" record has 

 been made of these disturbed periods. For a study of 

 days representing least disturbed, fair-weather condi- 

 tions, the twenty-one days having disturbed periods 

 should be excluded. 



Disturbed Hours. --Comparison of the periods of 

 disturbance tabulated under "disturbed hours" with the 

 disturbed periods noted in the table in section VII under 

 "remarks," indicates that bad weather conspicuously 

 affected Ixath the potential-gradient and conductivity dur- 

 ing two periods of several days each. Bad weather was 

 encountered from October 7 to 13 and from October 24 

 to November 2, and during these two intervals many low 

 values of conductivity are found, with simultaneous dis- 

 turbed values of potential-gradient. 



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