2 



OCEAN ATMOSPHERIC-ELECTRIC RESULTS 



land. Other effects such as have been mentioned already, 

 however, and which are of very local origin, are there 

 entangled with the general world-wide effect. Thus we 

 see here evidence of a phenomenon world-wide in ex- 

 tent and simultaneous in occurrence, the manifestation 

 of a factor which affects the entire earth at the same in- 

 stant of time and which waxes and wanes in a regular 

 manner throughout the day. This factor is likely the 

 supply current. That it was possible to make a discov- 

 ery of such far-reaching importance on the basis of the 

 relatively small amount of data available at the time 

 emphasizes not only the feasibility of measurements at 

 sea but also the advantage of studying atmospheric- 

 electric phenomena under the relatively simple condi- 

 tions which prevail over the oceans. Under simple con- 

 ditions fewer data are required in a given locality and 

 with a moving observatory measurements at widely dis- 

 tributed localities may be obtained, a point of importance 

 to the study of a world problem. On cruise VII, for the 

 first time at sea, the potential-gradient measurements 

 were made with a recorder instead of with eye-reading 

 apparatus, and many days of record obtained. 



In order to ascertain the effects of the various fac- 

 tors which determine the conductivity of the air at sea, 

 measurements were made on cruise VU of both positive 

 and negative conductivity, of ionic density, of the pene- 

 trating radiation, of the radioactive content of air at sea, 

 and of the number of condensation nuclei. During the 

 earlier part of the cruise the conductivity was meas- 

 ured by an eye-reading method, but beginning at San 

 Francisco the apparatus which provided a continuous 

 photographic record was used. The other measurements 

 were obtained with eye-reading instruments. An addi- 

 tional instrument for measuring penetrating radiation and 

 of a type different from that used on the Carnegie since 

 1915, including the present cruise, was put into use at 

 Hamburg. The purpose of this was both to ascertain 

 more definitely the absolute amount of ionization which 



is produced in the air by this source and to ascertain 

 whether variations occur in this factor. In addition to 

 the regular daily program of all these measurements, 

 series extending throughout twenty-four consecutive 

 hours were made as frequently as possible for the pur- 

 pose of studying the diurnal variation. 



Over 250 complete daily observations were obtained 

 for each of the several elements included in the program. 

 The diurnal-variation series, which were scheduled to be 

 made at weekly intervals, were attempted on thirty-two 

 occasions. Several of the series could not be completed 

 because of the development of instrumental difficulties or 

 unfavorable weather. Completed series ranged from 

 sixteen in the case of nuclei concentration, to twenty- 

 seven in the case of conductivity, with the series for 

 small-ion concentration being completed on twenty oc- 

 casions. It is also of considerable interest to note that 

 satisfactory records of air potentials were obtained be- 

 tween August 7, 1928 and November 18, 1929, for 181 

 complete days, of which 160 days were free from nega- 

 tive potential, and that in the interval between San Fran- 

 cisco and Apia, Samoa, September 3 to November 18, 

 1929, complete and satisfactory records of conductivity 

 were obtained for 58 days. Thus the recorders yielded 

 satisfactory data at a rate which in the case of the poten- 

 tial-gradient was eight times, and in the case of the con- 

 ductivity twelve times, the rate maintained when using 

 eye-reading methods for diurnal -variation series. 



The gratifying success of this program in great 

 measure is owing to the interest of the Commander, J. P. 

 Ault, to the enthusiasm, diligence, and skill of W. C. 

 Parkinson, senior scientific officer, who was in charge 

 of the atmospheric-electric work throughout the cruise, 

 and to O. W. Torreson, executive officer from Washing- 

 ton to San Francisco, and S. E. Forbush, executive offi- 

 cer from San Francisco to Apia, who aside from their 

 other duties assisted in various parts of this work. 



