Atmospheric-Electric Observations, 1910-13 



371 



known to exist on land. In most of the passages both the potential-gradient and X+/X- 

 decrease with increase of the conductivity, and in the final mean this relation is shown very 

 clearly. In the various portions of the passage from Tahiti to New York, large values of 

 the conductivity correspond to small values of the relative humidity, and vice versa. In 

 the first half of the cruise, from New York to Tahiti, this relation is not clearly indicated 

 in the separate portions, but it is revealed in the final means from New York to Colombo 

 and from Manila to Tahiti. There is also a clear relation between the conductivity and 

 temperature, increase of temperature corresponding to the increase in conductivity. 

 Increase of the conductivity is accompanied by little change in the absolute humidity. It 

 was thought that possibly solar radiations might in some way affect the conductivity at the 

 surface of the Earth, so that the observations of the cloudiness of the sky were grouped 

 according to the conductivities. There does not appear to be any relation here, however, 

 so we may conclude that there are no radiations from above or without which are cut off 

 by the presence of clouds and which affect the conductivity. Large values of the conduc- 

 tivity seem to correspond to large values of atmospheric pressure, but the relation here is 

 probably indirect in nature, as it is difficult to see how such small changes Ln the pressure 

 could affect appreciably the rate of production, the rate of recombination, or the specific 

 velocities of the ions. 



Table 74. — Mean Resulting Values for Cruise II of the Carnegie. 



The large mean value of the conductivity found in this work, combined with the 

 uncertainty which exists in regard to the dependence of the ionization of the atmosphere 

 on its radioactivity, makes it interesting to consider the observations of the atmospheric 

 conductivity from another standpoint. It has always been the custom to attribute a large 

 part of the ionization of the atmosphere to the radioactive constituents diffused throughout 

 it. The continual supply of these materials has been regarded as due to the diffusion of 

 radioactive emanations into the atmosphere through the pores of the ground. Since the 

 Pacific, Atlantic, and Indian Oceans are successively smaller in size, one would expect any 

 effect on atmospheric phenomena, due to the land, to be successively greater in the three 

 oceans, in the order named. It is therefore interesting to compare the mean values of the 

 conductivity as found over these three oceans. Table 75 contains these data. 



Table 75. — Regarding the Conductirily Over Ihe Various Oceans. 



The influence of the land is markedly shown. The results of this table made it seem 

 worth while to sort all the separate values of the conductivity into two groups, according 

 to the nearness of land and the general direction of the wind which prevailed at the times 

 of the separate observations. In one of these groups, which will be designated as "land- 

 wind," have been placed all the values of the conductivity which correspond to winds 



