410 



Reports on Special Researches 



Table 90. — Ionic Content (Ocean Values). 



Table 91. — Conduciivity (Ocean Values). 



responding to the Whole 

 (Land Values).* 



Year 



POTENTIAL-GRADIENT. 



Table 92 shows a collection of land results for the daily mean values of the potential- 

 gradient corresponding to the whole year, as obtained in different ^.^^^^ go.-Daily Mean Vah^s 

 locaUties. The mean of these values is 151 volts per meter, and of the Potential-Gradient Cor- 

 the value 113 volts per meter recorded in Table 85, as the mean 

 value for the Pacific and sub-Antarctic is of the same order 

 of magnitude, though somewhat smaller. Only on three occasions 

 during the whole cruise were negative potential-gradients ob- 

 served. These negative values have been omitted in takuig 

 the means. 



As regards ocean values obtained by other observers, these 

 are not very numerous, for many who have made measurements 

 of the potential-gradient on the sea have obtained only relative 

 values. Johnston' obtamed the value 93 volts per meter on the 

 third cruise of the Carnegie in the North Atlantic Ocean in 1914; 

 Simpson and Wright" obtained, in the South Atlantic and 

 South Indian Oceans, values which appear to show a minimum 

 of about 80 volts per meter in the neighborhood of 12 noon. 

 Angenheister^ found values ranging from 81 to 112 volts per 

 meter in the Red Sea, and values ranging from 75 to 97 volts 

 per meter in the Indian Ocean, while as early as 1907, Dike,* 

 observing on the Galilee, in the Pacific Ocean, came to the con- 

 clusion that the potential-gradient was of the order of magnitude of 90 volts per meter. 



*See E. von Schweidler and 

 K. W. F. Kohlrauseh: Article on 

 Almoaphiiri.'iche Ekklrizilfll (a sec- 

 tion from volume 3 of "Handbuch 

 der Elektrizitiit und des Magne- 

 tismus"). P- 247; the value for 

 Kew has, however, been altered in 

 accordance with Phil. Trans. R. 

 Soc. A, vol. 215, p. 140, 1915. 



'See page 373. 



'Proc. R. Soc. A, vol. 85, p. 175. 1911. 



'Giiltingen Xach. Ges. WiS.i., 1914. 



^See page 384. 



