Atmospheric-Electric Observations, 1910-13 369 



The evidence thus points to the absence of any considerable quantity of thorium emanation 

 in the air over the ocean. 



It will be noticed that on several days, when the vessel was very far from land, very 

 little activity was collected; particularly was this the case on December 11, 14, and 18, 

 1909. The region in which this happened was a very calm one, and the air had probably 

 not been in contact with the land for many days. It is thought, therefore, that the land is 

 the chief source of the radioactive matter in sea-au'. This is what would be expected from 

 determinations of the radium content of sea-water. The fact that Dike in his observations 

 on the Galilee in the Pacific could obtain no evidence of radioactivity, except near land, also 

 points to this conclusion. The Pacific Ocean being so much greater in extent than the 

 Atlantic, there should be much larger tracts over which the air had lost any radioactivity 

 gained from the land. The absence of thorium emanation would tend to confirm this 

 theory. 



It is easy to understand that the an- in the North Atlantic between Newfoundland and 

 England may at times have all been over land surfaces within a week. This may account 

 for the results obtained by Eve in this region.^ Observations comparing the amounts of 

 radioactivity over land and ocean are badly wanted. 



OBSERVATIONS ON CRUISE II OF THE CARNEGIE. 1910-1913. 



(W. J. Peters in Command.) 



The second cruise of the Carnegie is shown by heavy lines on the accompanying map, 

 Figure 17. The atmospheric-electric observations were made in continuance of the Director's 

 plan of scientific work for the Carnegie. The observers were: E. Kidson, H. F. Johnston, 

 and C. W. Hewlett. The final reduction and discussion of the observations were made by 

 C. W. Hewlett, under the direction of W. F. G Swann. The following extracts are taken 

 from the former's report; for the complete tables of observations, reference must be made 

 to the original.^ 



The atmospheric-electric work on the Carnegie's second cruise was confined to observa- 

 tions of the specific conductivity, the potential-gradient, and the radioactivity of the atmos- 

 phere, the greater part of the observations consisting of the first two quantities named. 

 The observations are divided naturally into three principal groups, according to the 

 observer who made them. From New York to Colombo, E. Kidson conducted the 

 observations ; for the route from Colombo to Manila, owing to breakage in the instruments 

 and the unpossibiUty of having the requisite repairs made, there are no observations; from 

 Manila to Tahiti, H. F. Johnston conducted the observations, and from Tahiti to New 

 York, the work was carried on by C. W. Hewlett. 



During the Carnegie's visit to Talcahuano and Coronel Bay, Observer Hewlett had 

 the opportunity of visiting the Instituto Central Meteorologico y Geofisico de Chile and 

 received from the Director, W. Knoche, much valuable counsel as regards atmospheric- 

 electric measurements. 



For the potential-gradient measurements, which, however, are only relative, Kidson 

 and Johnston used two radium-collectors, suspended on a bamboo pole, extending aft from 

 the stern tafTrail; in Hewlett's observations ionium-collectors were employed. 



For the conductivity measurements the same Gerdien apparatus (see PI. 15, Fig. 4) 

 was used throughout the cruise, except that Kidson used a Lutz string electroscope, while 

 Johnston and Hewlett made use of a Wiechert electroscope. All observations have been 

 corrected for natural leak, and they were usually made in the forenoon, between 8 and 1 1 

 o'clock. 



For estimations of the radioactive content, the Elster-and-Geitel method was employed 

 throughout the cruise. 



'A. S. Eve, Ten: Mag., vol. 14, p. 2.5, 1909. ^Terr. Mag., vol. 19, pp. 127-170, 1914. 



