152 



OCEAN ATMOSPHERIC-ELECTRIC RESULTS 



meters and then, from 12h to 24h, conditions within the 

 layer changed while the height remained essentially con- 

 stant. At 24h, the columnar resistance, R, had become 

 4.31 X 109 esu, or about fourfold as great as that pre- 

 vailijig before flh. 



All through the following day, September 10, con- 

 ductivity remained at approximately the same value as 

 that found for the last two hours of Septeml)er 9, and the 

 potential-gradient also remained essentially at the value 

 established at that time, so that a disturbed lower layer 

 of about 1 km thickness is indicated for all of the tenth. 

 When the disturbed region was entered at llh GMT or 

 2h LMT on the ninth, the ship was between five and six 

 hundred miles southwest of San Francisco, and in the 

 following ten days or more during which the disturbed 

 region appeared to persist, approximately one thousand 

 miles were traversed. As the ship was sailing in a gen- 

 erally southwest direction the extent of the disturbed re- 

 gion in that direction was one thousand miles; what 

 width the region might have had at right angles to the 

 course cannot be stated, but it is possible that it may 

 have been narrow, perhaps confined only to the width of 

 the steamer lane of the ships regularly plying between 

 San Francisco and Honolulu. Smoke from the ships 

 might be the disturbing factor in this region, although the 

 measurements of condensation nuclei on the Carnegie did 



not show particularly high concentrations, as indicated by 

 the nuclei data in section V. 



In conclusion, one may summarize the preceding 

 discussion of air-earth current density data derived from 

 the atmospheric-electric measurements on cruise VII of 

 the Carnegie , as follows: (1) Air-earth current density 

 varies through the day according to universal time, with 

 minimum values on normal, least -disturbed days not 

 infrequently as low as 5 x 10-7 esu and maximum values 

 as high as 15 x 10-V esu; (2) when the current density is 

 affected by the presence of a disturbing element in the 

 lower atmosphere, the latter may exist in a layer adja- 

 cent to the earth's surface only a few meters thick or as 

 much as a few kilometers thick, and the thickness to- 

 gether with the concentration of disturbing material in 

 the layer, may be such as to reduce the current density 

 to only a small fraction of its normal value; (3) the hori- 

 zontal extent of the layer containing the disturbing ele- 

 ment may be hundreds of miles; (4) the disturlied condi- 

 tion may manifest itself as mist, fog, or haze, but may 

 also have no visible manifestation and yet be equally ef- 

 fective in producing l^rge departures from normal in the 

 atmospheric-electric elements; (5) passage from a nor- 

 mal, least-disturbed region into a disturbed region may 

 be very abrupt. 



LITERATURE CITED 



1. Gish, O. H. 1939. Terrestrial magnetism and elec- 



tricity. Physics of the earth, vol. 8, pp. 149-230. 



2. Wait, G. R., and H. U. Sverdrup. 1927. Preliminary 



note on electromotive forces possibly produced by 

 the earth's rotating magnetic field and on observed 

 diurnal variation of the atmospheric potential-gra- 

 dient. Terr. Mag., vol. 32, pp. 73-83. 



3. Ault, J. P. 1945. The work of the Carnegie and sug- 



gestions for future scientific cruises. Oceanogr.- 

 rv. Scientific results of cruise VII of the Carnegie 



during 1928-29 under command of Captain J. P. 

 Ault, ClWPub. No. 571, pp. 1-17. 



4. Gish, O. H. 1942. Further evidence of a latitude- 



effect in potential-gradient. Terr. Mag., vol. 47, pp. 

 323-324. 



5. Wait, G. R. 1942. Electrical resistance of a vertical 



column of air over Watheroo (Western Australia) 

 and over Huancayo (Peru). Terr. Mag., vol. 47, pp. 

 243-249. 



