132 



OCEAN ATMOSPHERIC-ELECTRIC RESULTS 



Table 5. Reduction factor observations for potential-gradient, Atlantic Ocean, Carnegie cruise VII 



Recorder 4946 at stern 



Date 



GMT 



Begin 



End 



Potential-gradient 



Land 

 re- 

 cord- 

 er 



Ship's 

 stern 

 re- 

 cord- 

 er 



Reduction factor for 

 ship's stern recorder 



MUBP MUBS MDBP MDBS 



Rennarks 



Comparison of the Barbados results with those ob- 

 tained at Iceland indicates that both sets of results are 

 in general agreement, for individual values are found 

 among the Barbados results which are identical with the 

 Iceland values. The greater body of material for Bar- 

 bados provides a better basis for establishing the mag- 

 nitudes of the reduction factors than does the small 

 amount of material obtained at Iceland. 



In applying the reduction factors obtained at Iceland 

 and Barbados to the measurements tabulated in preced- 

 ing sections of this volume, it was considered desirable 

 to use a value to only one decimal, and therefore the 

 factor was taken as 0.7. This was employed for conver- 

 sion of all values of recorded volts obtained with the 

 long, bent collector rod which was in use until November 

 5, 1928, but with which the last satisfactory records 

 were obtained on October 11, 1928. The ship was at 

 Balboa from October 12 to 25, but at sea from October 

 25 to November 5 bad weather prevented successful re- 

 cording with that type of rod. 



Having the Barbados value of 0.67 for the mainsail 

 boom to port or starboard with the mainsail either up or 

 down, and having the data given in table 4 for the ratio 

 of stern recorder to stern eye-reading measurements, 

 namely, 0.23 for MUBP and 0.22 for MUBS, reduction 

 factors for the eye-reading apparatus are readily ob- 

 tained. Using the ratios 0.67/0.23 and 0.67/0.22, the 

 factors become 2.91 and 3.05, or 3.0 as an average value 

 taken to one decimal place. This agrees better with the 

 Kitts Point factor of 3.3 than with the value of 2.2 ob- 

 tained at Iceland, and on the basis of this result all po- 

 tentials measured with the eye -reading apparatus (ta- 

 bulated in tables 1 and 2), were converted to volts per 

 meter with a reduction factor of 3.3 for either MUBP or 

 MUBS, regardless of whether the measurements were 

 made before or after installation of the recorder appa- 

 ratus on the stern rail on July 7. 



For series 4 and 5 of the reduction factor observa- 

 tions, made at Easter Island and Apia, Samoa, respec- 

 tively, the instrumental conditions and arrangements on 



the ship were identical. Presumably, therefore, the fac- 

 tors obtained should have been the same. Both series 

 extended over many hours. No entirely satisfactory 

 data were obtained at Easter Island, however, because 

 of instrumental difficulties and bad weather. At Apia 

 the conditions were much better. 



At Easter Island ship and shore recorders were 

 operated for a period of fifty-four hours. Throughout 

 the interval the sky was cloudy to overcast and for much 

 of the time threatening, and drizzling rain or showers 

 fell at several different times. On one occasion the 

 supporting insulators for the stretched-wire system of 

 the shore installation became wet with rain; on other 

 occasions raincoats or pieces of canvas were placed 

 over the insulators and recording was suspended. Alto- 

 gether, twenty-seven hours of recording were made un- 

 usable by bad weather. 



In addition to bad weather, spiders caused frequent 

 trouble by spinningwebs in the cap of the shore electrom- 

 eter and in the caps of the supporting insulators of the 

 stretched-wire system. The spiders were numerous. 

 Several hours of record were affected by the presence of 

 spider webs. Instrumental difficulties, aggravated by the 

 bad weather, caused additional loss of record. Fogging of 

 the shore record during the daylight hours was a difficulty 

 that had been thought to be eliminated, but was not. Other 

 difficulties included failure of hourly zero marks, and un- 

 satisfactory focus of the electrometer telescope. 



Of the fifty-four hours of recording, it was found 

 that only three hours gave undisturbed, legible records 

 at the ship and on shore, namely, 2 hours to 5 hours on 

 December 10, GMT. Even during this interval, however, 

 it is apparent that the shore recorder was only slowly 

 recovering from poor insulation, and of the three hours 

 only the last can l9e taken as indicative of the proper 

 magnitude of the potential-gradient at the shore station. 

 From this shore value and the simultaneous ship's 

 value, the reduction factor obtained is 3.0 for MUBS, 

 which is in good agreement with the value of 3.2 obtained 

 four months later at Apia, Samoa (series 5). 



