STUDIES IN ATMOSPHERIC ELECTRICITY 



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Table 6. Reduction factor observations for potential-gradient, Pacific Ocean, Carnepie cruise VII 

 Potential-gradient apparatus no. 2 and recorder 4946 at stern 



Date 



GMT 



Begin End 



Potential-gradient 

 recorder 



Land 



Ship's 

 stern 



Reduction factor for 

 ship's stern recorder 



MUBP 



MUBS MDBPC 



Remarks 



1.63 

 2.29 

 3.01 



Recorder 4947 on shore 



Eye electrometer no. 28 at stern 



Ship'sdraft 12.1 ft. for'd, 13.4ft. aft. 



Ship anchored one-half mile from shore station. On November 5, 1928 the bent-arm collector rod was re- 

 placed by a short vertical rod approximately 0.5 meter long. 



Table 7. Reduction factor observations for potential-gradient. Pacific Ocean, Carnegie cruise Vn 



In addition to the measurements made with the re- 

 corders at Easter Island, nine twenty-minute sets of 

 measurements were made with the eye-reading appara- 

 tus which was still located on the stern rail. This appa- 

 ratus had not been in use since September 16, 1928, 

 nearly three months earlier, but initially it appeared to 

 be in good working condition. Examination of the nine 

 sets of data, however, disclosed that the electrometer 

 was very insensitive in its response to changes in air 

 potentials. Furthermore, the calibration was found to 

 differ greatly from calibrations made in September and 

 earlier, indicating that the electrometer fibers may 

 have become defective in the intervening months. This 

 fact, coupled v/ith the generally unfavorable behavior of 

 the shore apparatus, made it necessary to regard the 

 reduction factors obtained from these data as of no 

 value. 



Series 5, made at Samoa, utilized measurements 

 obtainod with the potential-gradient apparatus of the Apia 

 Magnetic Observatory. First, however, reduction-factor 

 apparatus belonging to the ship was set up on a reef 

 known as Watson's Island, this reef being situated off- 

 shore from Apia Observatory about three or four hun- 

 dred meters and within the confines of the harbor. The 

 Watson's Island apparatus was operated simultaneously 

 v/ith the Apia Observatory apparatus and the ship's re- 

 corder for a period of five hours on April 11, and reduc- 

 tion factors for both ship's apparatus and observatory 

 apparatus so were obtained. On the basis of the reduction 

 factor thus obtained for Apia Observatory, more than 



fifty hours of observatory recording was reduced to volts 

 per meter over a period from April 10 to 13. During 

 this time the ship's recorder was also operating, and 

 factors for the latter, under different sail positions, 

 were determined from comparison of the ship and ob- 

 servatory records. Unfortunately, these data v/ere re- 

 tained on the ship until the time of her destruction and 

 the papers were then lost, so that only a summary of the 

 results can be presented in table 7, together with the 

 preliminary work of April 11. 



To augment the results obtained from the reduction 

 factor observations in Apia harbor, the atmospheric po- 

 tentials measured with the ship's recorder over a period 

 of several hours after leaving the harbor on April 20, 

 v/ere compared vith simultaneous Apia land values after 

 reducing the l£:tter to volts per meter. Table 8 contains 

 thirteen hours of simultaneous measurements. Two po- 

 sitions of the mainsail boom were involved, and reduc- 

 tion factors for these two positions were obtained. It is 

 noted in table 8 that the ship's values for the first two 

 hours v/ere somewhat disturbed; this was true also for 

 the third hour when, in addition to the disturbance, the 

 change in sail position made the value questionable. 

 Since the ship already was several miles away from Apia 

 when these disturbed hours v/ere recorded, it is probable 

 that the effect of the disturbance was not the same at 

 both places. The factors 2.64 for MUBP and 3.80 for 

 MUBS, however, are in fair agreement with the values 

 shown in table 7 for these p)ositions, 2.87 and 3.28, re- 

 spectively. 



