IX. STUDIES IN ATMOSPHERIC ELECTRICITY 



DETERMINATION OF REDUCTION FACTORS FOR THE CONVERSION OF MEASURED VOLTS TO 

 POTENTIAL- GRADIENT IN VOLTS PER METER FOR CRUISE VD, CARNEGIE, 1928-1929 



In preceding sections of this volume values of po- 

 tential-gradient have been tabulated in volts per meter, 

 representative of conditions over an open, level expanse 

 of the ocean. To convert measured volts, obtained with 

 eye-reading and recording apparatus at the ship's stern, 

 to volts per meter, conversion or reduction factors 

 were determined on five separate occasions while the 

 ship was in port. On these occasions, measurements 

 were made of potential-gradient directly in volts per 

 meter at suitable shore stations while simultaneous 

 measurements in terms of volts were made on the ship 

 anchored as near the shore stations as possible. The 

 procedure has been described on page 5. The five se- 

 ries of reduction factor determinations were made at 

 the following times and places. 



Series 1 and 2 gave reduction factors for the stern 

 eye-reading apparatus no. 2; series 2 to 5 gave factors 

 for a recorder apparatus. For series 1, at Kitts Point, 

 only the eye-reading apparatus was on the stern rail. 

 On July 7, 1928, while at Hamburg, Germany, the re- 

 corder was installed on the stern rail, adjacent to the 

 eye-reading apparatus, and was equipped with a long, 

 bent collector rod. Series 2 and 3 were made with this 

 arrangement of apparatus. On November 5, 1928, after 

 an especially stormy period at sea, the bent rod was 

 discarded and a short, straight collector rod installed 

 on the recorder, and series 4 and 5 were made with this 

 final arrangement. 



Although it was recognized that the changes in ap- 

 paratus would alter the reduction factors, examination 

 of the five series showed discrepancies too great to be 

 attributed to instrumental changes alone. Detailed ex- 

 amination therefore was undertaken of the whole body of 

 potential-gradient data, and the present paper deals with 

 that examination. Table 1 is a summary of the reduction 

 factors obtained at the different stations. In this table 

 the letters MUBP, etc., have the meanings given in ear- 

 lier sections of this volume. 



For the first series, made at Kitts Point, the eye- 

 reading apparatus was mounted alone on the stern rail 

 and was the same equipment as that used on previous 

 cruises. The disposition of ship's gear in the vicinity of 

 the stern rail was the same as for previous cruises ex- 

 cept for one item. The one change was the installation 

 of a small lifeboat at the stern port corner of the quarter- 

 deck, hung in davits which stood approximately three 

 meters above the deck and which projected out over the 

 water somewhat less than one meter. One davit stood 

 very near the stern rail, and a slight increase in the 

 reduction factors might have been expected from its 

 presence as well as from the presence of the lifeboat. 



Seventeen 20-minute sets of measurements were 

 made with eye-reading apparatus on the ship and on 

 shore at the Kitts Point station on May 5, between lOh 

 30m and 19h 00m LMT. Recorder apparatus also was 

 used at the shore station, connected in parallel with the 

 eye-reading electrometer, and a satisfactory photographic 

 record obtained over the period llh 00m to 19h 00m. 

 Comparison of the latter with the shore eye-reading 

 measurements gave identical values of volts per meter, 

 indicating that both measuring instruments were in good 

 order. The first five of the seventeen sets of data were 

 discarded because they differed so markedly from the 

 remaining twelve. The large difference was attributed 

 to the effect of wind conditions. There was only light 

 wind during the earlier observations, and possibly the 

 potential-gradient at the land station was different from 

 that at the ship on that account. As the win1 came up 



Table 1. Summary of reduction factor results, Carnegi e cruise VII 



^Mean value for MUBP and MDBP is 3.28. The comparable factor for MUBP (and MUBS) for previous 

 cruises is 2.85. "The factor for MDBPC for previous cruises is 3.77. 



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