| Station. | Authority. | I+ | I− | Q |
| Freiburg | Gockel | 0.34 | 0.24 | 1.41 |
| Karasjok | Simpson | 0.38 | 0.33 | 1.17 |
| Mattsee | von Schweidler | 0.35 | 0.29 | 1.19 |
| Seewalchen | von Schweidler | 0.45 | 0.38 | 1.17 |
Gockel’s mean values of I+ and Q would be reduced to 0.31 and 1.38 respectively if his values for July—which appear abnormal—were omitted. I+ and I− both show a considerable range of values, even at the same place during the same season of the year. Thus at Seewalchen in the course of a month’s observations at 3 P.M., I+ varied from 0.31 to 0.67, and I− from 0.17 to 0.67.
There seems a fairly well marked annual variation in ionic contents, as the following figures will show. Summer and winter represent each six months and the results are arithmetic means of the monthly values.
| Freiburg. | Karasjok. | |||||
| I+ | I− | Q | I+ | I− | Q | |
| Winter | 0.29 | 0.21 | 1.49 | 0.33 | 0.27 | 1.22 |
| Summer | 0.39 | 0.28 | 1.34 | 0.44 | 0.39 | 1.13 |
If the exceptional July values at Freiburg were omitted, the summer values of I+ and Q would become 0.33 and 1.25 respectively.
18. Diurnal Variation.—At Karasjok Simpson found the mean values of I+ and I− throughout the whole year much the same between noon and 1 P.M. as between 8 and 9 A.M. Observations between 6 and 7 P.M. gave means slightly lower than those from the earlier hours, but the difference was only about 5% in I+ and 10% in I−. The evening values of Q were on the whole the largest. At Freiburg, Gockel found I+ and I− decidedly larger in the early afternoon than in either the morning or the late evening hours. His greatest and least mean hourly values and the hours of their occurrence are as follows:—
| Winter. | Summer. | ||||||
| I+ | I− | I+ | I− | ||||
| Max. | Min. | Max. | Min. | Max. | Min. | Max. | Min. |
| 0.333 | 0.193 | 0.242 | 0.130 | 0.430 | 0.244 | 0.333 | 0.192 |
| 2 PM | 7 PM | 2 PM | 8 PM | 4 PM | 9 to | 4 PM | 9 to |
| 10 PM | 10 PM | ||||||
Gockel did not observe between 10 P.M. and 7 A.M.
19. Ionization seems to increase notably as temperature rises. Thus at Karasjok Simpson found for mean values:—
| Temp. less than −20° | −10° to −5° | 10° to 15° |
| I+ = 0.18, I− = 0.36 | I+ = 0.36, I− = 0.30 | I+ = 0.45, I− = 0.43 |