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Reports on Special Researches 



indicating a higher active content in winter than in summer. Table 77 shows the mean 

 values of the various elements arranged according to the period as given in the first column, 

 X+ and X_ referring, respectively, to the conductivities for positive and negative ions. The 

 quantity rj in the last column is proportional to the radioactive content of the atmosphere. 

 No marked variation of the atmospheric-electric elements with temperature or 

 humidity was found; however, an indication is shown of a variation of the conductivity 

 with latitude, a maximum for the latitudes involved occurring in the neighborhood of 50° 

 north. These conclusions with regard to the variation of the elements with season, latitude, 

 etc., must be looked upon as tentative, owing to the small number of data involved. A 

 comparison has been made of the mean values of the conductivity for the several sections 

 of the cruise, with the values to be expected as a result of the measured radioactive content. 



Table 77. — Atmospheric-Eleciric Elements Grouped According to Period of Year. 



The results are given in Table 78. They have been calculated by reducing the measured 

 radioactive content to Elster-and-Geitel units and then making use of an empirical relation 

 obtained by Kurz for the rate of production of ions per cubic centimeter corresponding to 1 

 Elster-and-Geitel unit. In the table, q represents the rate of production of ions per cubic 

 centimeter owing to the radioactive material, and the number of ions (n) per cubic centi- 

 meter of either sign has been calculated from the expression n- = q/a, where a is the coeffi- 

 cient of recombination of the ions and is taken as 2.5X 10~^ The conductivity is taken as 

 2nev, V being the specific velocity of the ions. The value of r has been taken as 1.3 cm. per 

 second per volt per centimeter for each sign of ions.^ 



Table 78. — Effect of Radioactive Material in Determining Ionization and Conductivity. 



In the observations in Long Island Sound, n was measured directly for each kind of 

 ion, and so it became possible there to compare the measured value of n++n_ with the 

 calculated 2n without introducing the specific velocity of the ions. In the above calculated 



'There is a good deal of uncertainty as to the value which should be taken for a. In the original report the value 1.56 X 10- », 

 as quoted for laboratory experiments, was used. Measurements on atmospheric ions have given varied results for o, 

 Bome values ranging aa high as 3. OX 10-*. In the general discussion of the results which forms part of the report on the 

 Carnegie's fourth cruise, the value 2.5X10-' has been tentatively adopted. Again, the results of the fourth cruise indicate, 

 for the ocean, a value of v about 1.3 cm. per second per volt per centimeter instead of the value 1.6 which was tentatively 

 used in the report on the third cruise. The empirical relation obtained by Kurz has also suffered corrections at the hands of 

 Kohlrausch and others (see page 416). For the sake of uniformity in relation to the discussion of the Carnegie's fourth 

 cruise, those numbers in Table 78 which depend upon theoretical constants have been recalculated in the light of the above 

 considerations. 



