372 



Reports on Special Researches 



which had probably passed over large bodies of land within a week. In the other group, 

 designated "sea-wind," have been placed the remaining values of the conductivity which 

 correspond to winds which had probably been blowing for a week or more over water. 

 The sorting out was done independently by two persons, and Table 76 contains a summary of 

 this analysis. One very large value of the conductivity has been omitted in this calculation. 



Table 76. — Effect of Land on tite Condudivity at Sea. 



The summaries in both Tables 75 and 76 support A. Nippoldt's view,^ as based upon 

 the Galilee observations in the Pacific Ocean in 1907-08, that the effect of the land is to 

 increase the value of the conductivity as measured at sea. 



From a summary of the various results thus far obtained at sea, the following deduc- 

 tions in regard to the mean values of the elements may be drawn : The potential-gradient 

 is of the same order of magnitude over the sea as over the land; the radioactivity of the air 

 over ocean areas far removed from land is small compared to that found over land, and the 

 conductivity over the ocean is at least as large as that found over land. 



OBSERVATIONS ON CRUISE III OF THE CARNEGIE, 1914. 



(J. p. AuLT IN Command.) 



The general course followed by the Carnegie during her third cruise is shown in 

 Figure 18. The vessel left Brooklyn on June 8, 1914, arriving at Hanmaerfest on July 3. 

 SaiUng again from Hammerfest on July 25, she arrived at Reykjavik, Iceland, on August 24, 

 having reached the latitude of 79° 52' north, off the northwest coast of Spitzbergen. 

 Leaving Reykja\ik on September 15, the Carnegie arrived at Greenport on October 12, 

 returning to Brooklyn on October 21, 1914. 



The atmospheric-electric observations, which were made by Observer H. F. Johnston, 

 comprise measurements of the potential-gradient, conductivity, and radioactive content 

 of the atmosphere. In addition to these, a few observations were made in Long Island 

 Sound by W. F. G. Swann, for the purjjose of trying out certain new instruments and 

 methods with a view to their adoption in subsequent ocean work. The following are 

 extracts from W.F.G.Swann's report on the atmospheric-electric observations of the whole 

 cruise. For the complete tables of observations, reference must be made to the original.^ 



As the first portion of the report contains a discussion of certain instrumental errors 

 and corrections which will again be referred to in the account of the work on the next 

 cruise, this portion of the report will not be abstracted here. The atmospheric-electric 

 observations were always taken about the same time of day, between 9 a. m. and 12 noon. 



Measurements of the potential-gradient were made by means of an ionium-collector 

 suspended at the end of a bamboo pole which extended aft from the stern taffrail, and the 

 standardization of the potential-gradient apparatus was made by simultaneous ship-and- 

 shore observations on two occasions, the first at Reykjavik and the second at Gardiners 

 Bay. In the shore observations a method due to Simpson was employed, m which the ionium- 

 collector was fastened to the middle of a long wire stretched horizontally between two 

 poles. 



^Terr. Mag., vol. 17, pages 33-41. 1912. 



'Terr. Mwj.. vol. 20, pp. 13-48, 1915. 



