Table VIII.—Mean Values of a±.
| Wind Strength. | I±0 to 0.1. | 0.1 to 0.2 | 0.2 to 0.3 | 0.3 to 0.4 | 0.4 to 0.5 |
| 0 to 1 | 0.45 | 0.60 | 1.26 | 2.04 | 3.03 |
| 1 to 2 | 0.65 | 1.08 | 1.85 | 2.92 | 3.83 |
| 2 to 3 | .. | .. | 2.70 | 3.88 | 5.33 |
Simspon concluded that for a given wind velocity dissipation is practically a linear function of ionization.
24. Table IX. will give a general idea of the relations of potential gradient to dissipation and ionization.
Table IX.—Potential, Dissipation, Ionization.
| Potential gradients volts per metre. | q | Karasjok (Simpson (10)). | ||||||
| Kremsmünster (41). | Freiburg (43). | Rothhorn (43). | a+ | a− | I+ | I− | Q | |
| 0 to 50 | .. | 1.12 | .. | .. | .. | .. | .. | .. |
| 50 to 100 | 1.14 | 1.31 | .. | 4.29 | 4.67 | 0.43 | 0.39 | 1.11 |
| 100 to 150 | 1.24 | 1.69 | .. | 3.38 | 3.93 | 0.37 | 0.32 | 1.15 |
| 150 to 200 | 1.48 | 1.84 | .. | 1.85 | 2.58 | 0.36 | 0.28 | 1.28 |
| 200 to 300 | .. | .. | 3.21 | 1.37 | 1.58 | 0.26 | 0.19 | 1.42 |
| 300 to 400 | .. | .. | 4.33 | 0.60 | 0.85 | .. | .. | .. |
| 400 to 500 | .. | .. | 5.46 | .. | .. | .. | .. | .. |
| 500 to 700 | .. | .. | 8.75 | .. | .. | .. | .. | .. |
If we regard the potential gradient near the ground as representing a negative charge on the earth, then if the source of supply of that charge is unaffected the gradient will rise and become high when the operations by which discharge is promoted slacken their activity. A diminution in the number of positive ions would thus naturally be accompanied by a rise in potential gradient. Table IX. associates with rise in potential gradient a reduced number of both positive and negative ions and a diminished rate of dissipation whether of a negative or a positive charge. The rise in q and Q indicates that the diminished rate of dissipation is most marked for positive charges, and that negative ions are even more reduced then positive.
At Kremsmünster Zölss (41) finds a considerable similarity between the diurnal variations in q and in the potential gradient, the hours of the forenoon and afternoon maxima being nearly the same in the two cases.
No distinct relationship has yet been established between potential gradient and radioactivity. At Karasjok Simpson (10) found fairly similar mean values of A for two groups of observations, one confined to cases when the potential gradient exceeded +400 volts, the other confined to cases of negative gradient.
At Freiburg Gockel (55, 57) found that when observations were grouped according to the value of A there appeared a distinct rise in both a− and I+ with increasing A. For instance, when A lay between 100 and 150 the mean value of a- was 1.27 times greater than when A lay between 0 and 50; while when A lay between 120 and 150 the mean value of I+ was 1.53 times larger than when A lay between 0 and 30. These apparent relationships refer to mean values. In individual cases widely different values of a− or I+ are associated with the same value of A.