Atmospheric-Electric Observations, 1914 375 



values the effect of the penetrating radiation from the active material in the sea has been 

 neglected ; this effect is very small, however. It will be seen that while in the Atlantic Ocean 

 the radioactive material is sufficient to account for an appreciable fraction of the conduc- 

 tivity, it is, on the basis of the constants used, insufficient to account for all of it. It must 

 further be borne in mind that in so far as many of the ions produced by the radioactive 

 material in the air undoubtedly go into the type of the slowly moving Langevin ions, the 

 calculated conductivity should be even smaller; it is probably for this reason that the 

 calculated values of n^+n_ for the Long Island Sound observations come out greater than 

 the observed values. 



It is natural to expect a smaller radioactive content in the case of air which has been 

 for some time over the ocean than in the case of air which has passed recently over land. 

 If, then, making use of the wind records, we divide the days into two classes as regards the 

 probable time which has elapsed since the wind last traveled over land, we should expect a 

 higher radioactive content in the cases in which the wind has recently traveled over land 

 than in the others. The conclusion is borne out in 8 of 9 cases during the voyage from New 

 York to Hammerfest, and in the greater number of cases in the voyage from Iceland to 

 Greenport. No very definite conclusion in this respect emerges from a consideration of the 

 results of the voyage from Hammerfest to Iceland; but the winds on the voyage were 

 usually of a very small velocity, and it is consequently difficult to form much idea as to the 

 probable course which the air had pursued in the days preceding any one for which the 

 strength is recorded. 



In some cases, the conductivity appears to undergo an interesting change as one 

 passes from the American shore out into the open sea. The conductivity starts consider- 

 ably below its normal value, but increases again as one gets out into the open sea, a result 

 observed also by E. Kidson^ on the first cruise of the Carnegie. The values of the con- 

 ductivity were particularly low in Long Island Sound. 



Since both the conductivity and ionic content were measured in the Sound, it was 

 possible here to deduce the specific ionic velocities, v+ and v_ , for positive and negative ions. 

 The mean values of v+ and v_ so found are respectively 0.77 and 0.83 cm. per second per 

 volt per centuneter. These values are somewhat below normal, a result which is in har- 

 mony with the low values of the conductivity in indicating abnormal conditions in the region 

 of transition between sea and land. 



The latter portion of the report is devoted to a mathematical discussion of the possi- 

 bility of determining the nature and amount of active material m the atmosphere from an 

 analysis of the decay curves for the active wire. It appears that the customary method of 

 drawing conclusions as to the nature of the products in the atmosphere by comparing the 

 decay curves for a wire exposed thereto with that of a wu'e exposed to emanation con- 

 tamed in a small closed vessel, is not justified. The activity curves are analyzed in the 

 report, use being made of the theory of radioactive disintegration, and it is found that 

 while some of the curves can be explained by radium emanation alone, others require the 

 presence of a product of longer decay period than radium A, B, or C. The possibiUty of 

 this extra product being a product of thorium emanation, as is generally assumed to be the 

 case on land, is discussed. 



An attempt to calculate the actual amount of radium emanation in the ak directly 

 from the theory of the Elster-and-Geitel method, without assuming any empirical relation, 

 results m a much smaller value for the emanation content than that given by the empirical 

 relation, unless it is assumed that the average specific velocities of the active carriers are 

 much smaller than is generally supposed. 



'See page 367. 



