+--------------------------+-------+--------------+---------------------+------+------+
| Place. |Period.| Season. | Observer or | a[+-]| q |
| | | | Authority. | | |
+--------------------------+-------+--------------+---------------------+------+------+
| Karasjok | 1903-4| Year | Simpson (10) | 3.57 | 1.15 |
| Wolfenbuttel | Year | Elster & Geitel (39)| 1.33 | 1.05 |
| Potsdam | 1904 | Year | Ludeling (40) | 1.13 | 1.33 |
| Kremsmuster | 1902 | Year | Zolss (42) | 1.32 | 1.18 |
| " | 1903 | Year | Zolss (41) | 1.35 | 1.14 |
| Freiburg | | Year | Gockel (43) | .. | 1.41 |
| Innsbruck | 1902 | | Czermak (44) | 1.95 | 0.94 |
| " | 1905 | Jan. to June | Defant (45) | 1.47 | 1.17 |
| Mattsee (Salzburg) | 1905 | July to Sept.| von Schweidler (46) | .. | 0.99 |
| Seewalchen | 1904 | July to Sept.| von Schweidler (38) | .. | 1.18 |
| Trieste | 1902-3| Year | Mazelle (47) | 0.58 | 1.09 |
| Misdroy | 1902 | | Ludeling (40) | 1.09 | 1.58 |
| Swinemunde | 1904 |Aug. and Sept.| Ludeling (40) | 1.23 | 1.37 |
| Heligoland (sands) | 1903 | Summer | Elster & Geitel (40)| 1.14 | 1.71 |
| " plateau | " | " | " " (40)| 3.07 | 1.50 |
| Juist (Island) | | " | " " (48)| 1.56 | 1.56 |
| Atlantic and German Ocean| 1904 | August | Boltzmann (49) | 1.83 | 2.69 |
| Arosa (1800 m.) | 1903 |Feb. to April | Saake (50) | 1.79 | 1.22 |
| Rothhorn (2300 m.) | 1903 | September | Gockel (43) | .. | 5.31 |
| Sonnblick (3100 m.) | 1903 | September | Conrad (22) | .. | 1.75 |
| Mont Blanc (4810 m.) | 1902 | September | le Cadet (43) | .. |10.3 |
+--------------------------+-------+--------------+---------------------+------+------+
Table VI. gives the mean values of a[+-] and q found at various
places. The observations were usually confined to a few hours of the
day, very commonly between 11 A.M. and 1 P.M., and in absence of
information as to the diurnal variation it is impossible to say how
much this influences the results. The first eight stations lie inland;
that at Seewalchen (38) was, however, adjacent to a large lake. The
next five stations are on the coast or on islands. The final four are
at high levels. In the cases where the observations were confined to a
few months the representative nature of the results is more doubtful.
On mountain summits q tends to be large, i.e. a negative charge is
lost much faster than a positive charge. Apparently q has also a
tendency to be large near the sea, but this phenomenon is not seen at
Trieste. An exactly opposite phenomenon, it may be remarked, is seen
near waterfalls, q becoming very small. Only Innsbruck and Mattsee
give a mean value of q less than unity. Also, as later observations at
Innsbruck give more normal values for q, some doubt may be felt as to
the earlier observations there. The result for Mattsee seems less open
to doubt, for the observer, von Schweidler, had obtained a normal
value for q during the previous year at Seewalchen. Whilst the average
q in at least the great majority of stations exceeds unity, individual
observations making q less than unity are not rare. Thus in 1902 (51)
the percentage of cases in which q fell short of 1 was 30 at Trieste,
33 at Vienna, and 35 at Kremsmunster; at Innsbruck q was less than 1
on 58 days out of 98.
In a long series of observations, individual values of q show usually
a wide range. Thus during observations extending over more than a
year, q varied from 0.18 to 8.25 at Kremsmunster and from 0.11 to 3.00
at Trieste. The values of a+, a- and a[+-] also show large variations.
Thus at Trieste a+ varied from 0.12 to 4.07, and a- from 0.11 to 3.87;
at Vienna a+ varied from 0.32 to 7.10, and a- from 0.78 to 5.42; at
Kremsmunster a[+-] varied from 0.14 to 5.83.
14. _Annual Variation._--When observations are made at irregular
hours, or at only one or two fixed hours, it is doubtful how
representative they are. Results obtained at noon, for example,
probably differ more from the mean value for the 24 hours at one
season than at another. Most dissipation results are exposed to
considerable uncertainty on these grounds. Also it requires a long
series of years to give thoroughly representative results for any
element, and few stations possess more than a year or two's
dissipation data. Table VII. gives comparative results for winter
(October to March) and summer at a few stations, the value for the
season being the arithmetic mean from the individual months composing
it. At Karasjok (10), Simpson observed thrice a day; the summer value
there is nearly double the winter both for a+ and a-. The Kremsmunster
(42) figures show a smaller but still distinct excess in the summer
values. At Trieste (47), Mazelle's data from all days of the year show
no decided seasonal change in a+ or a-; but when days on which the
wind was high are excluded the summer value is decidedly the higher.
At Freiburg (43), q seems decidedly larger in winter than in summer;
at Karasjok and Trieste the seasonal effect in q seems small and
uncertain.