422 Reports on Special Researches 



SUMMARY OF CONCLUSIONS. 



A general discussion of the observations leads to the following general conclusions: 



(1) The potential-gradient over the ocean has, according to the present observations, 

 an average daily mean value of 113 volts per meter. It has a distinct diurnal variation 

 with minima about 5 a. m., and 3 p. m., and maxima about midnight and 9 a. m., the 12- 

 hour Fourier "wave" being more prominent than the 24-hour "wave." 



(2) The average values, for the whole cruise through March 1916, of conductivities 

 and ionic contents for positive and negative ions are, X+ = 1.44X 10"^, X_ = 1.19X10"* 

 E.S.U., n+ = 804, and n_ = 677, and the mean value of n^jn^ is 1.22. These numbers are 

 in close agreement with values found on land. The diurnal variation of n+ has been 

 investigated, and the element has been found to have a fiat maximum ranging from about 

 6 a. m. to 2 p. m. and a minimum about midnight. 



(3) The mean ocean value of the specific ionic velocities is 1.30 cm. per second per 

 volt per cm., and is the same for ions of both signs. It is somewhat greater than the 

 values «;+ = 1.08 and i;_ = 1.22 obtamed as the means for a number of land stations, but is 

 nearer to the ionic velocities as measured for ions artificially produced in dust-free air. 



(4) The mean ocean value for the air-earth current-density is 9.5X10"^ e.s.u. 



(5) The number of pairs of ions produced per c. c. per second in a closed copper vessel 

 over the ocean shows very Uttle variation with season or location, and there does not 

 appear to be any appreciable diurnal variation in the quantity. The mean absolute value 

 of the number in question is 3.8. It is considerably smaller than the values resulting from 

 corresponding measurements made on land, a result to be expected in view of the absence, 

 over the ocean, of the contribution to the penetrating radiation by radioactive materials. 



(6) The average radium-emanation contents found over the Pacific and sub-Antarctic 

 Oceans are respectively 3.3 X 10"^^ and 0.4 X lO'^^ curie per cubic meter. These values are 

 much smaller than the mean value (88 X lO^^'-" curie per cubic meter) for the land. They are 

 too small to contribute in a marked degree to the ionization over the ocean, and it is con- 

 cluded that the reason for the measured ionic densities over land being, if anything, smaller 

 than those over the ocean, is to be found m the greater purity of the ocean air as compared 

 with the land air. The presence of dust nuclei, in fact, increases the number of ions which 

 go into the slowly moving class, and which consequently lose their power of becoming regis- 

 tered in the usual measuring apparatus. 



As yet no detailed analysis of the observations has been made with a view to determin- 

 ing the interrelations between the atmospheric-electric quantities and latitude, temperature, 

 humidity, and atmospheric pressure. 



