THE RATIO OF POSITIVE TO NEGATIVE CONDUCTIVITY ON CRUISE VD 

 AND ITS VARIATION WITH POTENTIAL -GRADIENT 



In the preceding paper attention was called to the 

 similarity in diurnal variation of the ratio of positive to 

 negative conductivity and the potential-gradient, based 

 on measurements made on cruise Vn of the Carnegie . 

 The preceding paper was chiefly concerned with the 

 registrations of conductivity during the period Septem- 

 ber 3 to November 18, 1929, and simultaneous registra- 

 tions of potential-gradient. In figure 5 of that paper, the 

 graph showing the diurnal variation in ratio of the two 

 conductivities was shown to proceed to a maximum at 

 18h to 19h GMT, this being also the maximum of the po- 

 tential-gradient. The values of the ratio fell in the range 

 1.09 to 1.29, for changes in potential-gradient from 121 

 to 189 volts per meter. These data are presented again 

 in figure 9 of the present paper, where the ordinates 

 represent potential-gradient and the abscissas represent 

 the values of the ratio. It will be noted that the line 

 through the points, extrapolated back to a value of zero 

 potential-gradient, gives a value of the ratio at that point 

 of about 0.8 to 0.9. For values of the field approaching 

 zero, such a value of the ratio would be expected be- 

 cause the positive and negative small ions then would 

 approach numerical equality and only differences in 

 their mobilities would cause the ratio to depart from 

 unity. Since the mobility of the negative small ion is 

 greater than that of the positive small ion, the ratio of 

 the conductivities therefore would be less than unity. H 

 the value of positive small-ion mobility is, for example, 

 1.30 cm/sec/volt/cm, the mobility of the negative ion 

 would need to be only 1.53 to give a ratio of the conduc- 

 tivities of 0.85. In examining figure 9 it must be kept in 

 mind that the plotted points are mean values for approx- 

 imately twenty days of data, and that the range of values 

 of both elements is smaller than would be obtained by 

 other methods of handling the data. 



To explore further the relation between the conduc- 

 tivity ratio and the potential-gradient, the day by day ob- 

 servations tabulated in section V of the present volume 



were examined. The measurements given in that table 

 were obtained daily during a one- to two-hour observing 

 period in the afternoon. For the present discussion, 

 potential-gradient was taken as the independent variable 

 and the data grouped under specified ranges of values of 

 that element. The results of this treatment are shown 

 in table 1 . 



The data presented in table 1 were grouped sepa- 

 rately for the Atlantic and Pacific oceans because pre- 

 liminary inspection showed that the conductivity ratios 

 were consistently higher for given values of potential- 

 gradient for the Atlantic than for the Pacific. A further 

 reason for this grouping was the greater homogeneity 

 achieved within each group; a change in the potential- 

 gradient apparatus when entering the Pacific Ocean re- 

 quired the use of a different set of reduction-factor 

 values for the Pacific from those for the Atlantic poten- 

 tial-gradient data. 



The data of table 1 are plotted in figure 10 (except 

 the last group of two observations for the Atlantic), 

 where a linear relation is indicated between increasing 

 values of the conductivity ratio and increasing values of 

 potential-gradient. In figure 10, as in figure 9, extrapo- 

 lation back to zero potential-gradient of the line drawn 

 for the Pacific data, gives a value of the ratio between 

 0.8 and 0.9, which is very satisfactory agreement. For 

 the Atlantic the data are too few to provide a sound basis 

 for discussion; in fact, thirty-five out of forty-six ob- 

 servations, or 80 percent, in the range of 90 to 150 volts 

 per meter, could be viewed as supporting the idea that 

 the conductivity ratio is effectively constant at a value 

 of 1.16. On the basis of the more definite indication 

 given by the Pacific data, however, of an increase in 

 ratio with increase in potential-gradient, it has seemed 

 preferable to draw through the points for the Atlantic 

 data in the manner shown in figure 10. No satisfactory 

 explanation for the lack of agreement shown in figure 10 

 of the data for the two oceans presents itself at this time. 



Table 1. Values of recorded potential-gradient and corresponding computed values of \+/\- from 



daily eye readings of X + and \ - 



Meanor total 122 



1.17 



46 



172 



1.15 



152 



141 



