370 



Reports on Special Researches 



The mean values of the total conductivity, the ratio of the positive to the negative 

 conductivity, and the relative potential-gradients ai-e given in Table 74. It is to be 

 remarked that only on one occasion during the whole cruise was a negative potential-gradi- 

 ent observed, although observations were made frequently while it was raining. Usually 

 during rain the potential-gradient was very high, often exceeding the range which the 

 electroscope would measure, but it was always positive. On the one occasion when a nega- 



FiG. 17.— Cruise II of the Carnegie, 1910-1913. 



tive potential-gradient was observed the sky was nearly covered with clouds, but there was 

 no rain. Although the reduction factor for the potential-gradient was not measured on 

 this ciTjise it is deemed safe to say that the observations indicate a mean potential-gradient 

 of the order of magnitude of 120 volts per meter. The mean values of X+, X_, and X+/X_, 

 for the whole cruise are respectively 1.6lXlO~^E.s.u., 1.34X10-*e.s.u., and 1.23. During 

 the passage from Falmouth to New York, the observations of the radioactive content of 

 the atmosphere formed a fairly complete set. The mean value for this cruise, of the 

 activity, expressed in Elster-and-Geitel units, is 12.3, and the nature of the deposit on the 

 wire was such that the activity decayed to half value in about 40 minutes. 



It has been attempted to discover any relations which may exist between the various 

 atmospheric-electric elements or between these and the various meteorological factors. As 

 a rule, the relations which have been found agree with those which have been previously 



