Atmospheric-Electric Observations, 1914 



373 



The conductivity observations were made with Gerdien's instrument, the electroscope 

 being of the Wulf bifilar type. The radioactive content was measured by Elster-and- 

 Geitel's method, with certain modifications devised with a view to rendering the results 

 more susceptible of theoretical interpretation.^ 



In addition to the above, measurements of the ionic densities n+ and n_, for positive 

 and negative ions, were made in Long Island Sound by means of the special form of ion- 

 counter devised by W. F. G. Swann.^ 



The average value of the potential-gradient, atmospheric conductivity, and radio- 

 active content for the whole cruise were, respectively, 93 volts per meter, 2.52 X 10~^ e.s.u., 

 and 23. The last number is expressed in Elster-and-Geitel units. The average value of 

 the air-earth current-density for the whole cruise was 7.7X10"' E.s.u. 



Fia. 18.— Cruise III of the Carnegie, 1914. 



The observations, as far as they go, indicate a general increase of the potential-gradient 

 from summer to winter, which is in accord with land observations for the daily mean 

 values. The conductivity also shows a general increase from the beginning of the cruise 

 (June 8, 1914) to about the end of September, when a maximum occurs, after which the 

 conductivity falls; the air-earth current-density follows the general course of the conduc- 

 tivity. No very definite conclusions result as to the seasonal variations of the radioactive 

 content, though the observations are not inconsistent with those of Simpson in Lapland, in 



'See W. F. G. Swann, Terr. Mag., vol. 19, pp. 176-179, 1914. 



-See pages 387-389. 







