304 DR. C, CHREE: ATMOSPHERIC ELECTRIC POTENTIAL RESULTS AT KEW 
In such a case the value assigned to midnight in the mean data for a particular 
month varies slightly according as one makes midnight the first or the last hour of 
the day. 
When, instead of all the days in the month, one takes a limited number of a 
particular kind, a non-cyclic, or a-periodic, element may present itself in the diurnal 
inequality, though there is no such element present to an appreciable extent in the 
average day of the month. This phenomenon, for instance, as I have pointed out, is 
conspicuous in the horizontal component of the earth’s magnetic field on magnetically 
“quiet” days. 
There are two courses open in such a case, viz., to give the mean hourly values 
taken direct from the observations, with data for both midnights, or else to eliminate 
the non-cyclic element from the diurnal variation while stating its amount. 
The latter course has been adopted here. The size of the algebraic mean non-cyclic 
element for the selected days in individual months is recorded in Table II., in volts 
per metre. 
Table II. shows on the whole a rise of P throughout the average selected day, but 
the mean value of the non-cyclic element is very small, and its sign even varies from 
year to year. Coming to individual months, we see that in May the non-cyclic effect 
was negative in six out of the seven years; but in three years, 1900, 1901, and 1903, 
there were more individual days in which it was plus than minus. The only months 
in which there seems a decided tendency for P to rise during the 24 hours of a 
selected day are December and January. In the former month 42 days out of 68, 
and in the latter month 38 days out of 65, showed a rise. In December there was an 
excess of days showing a plus effect in six years out of the seven. 
Table II. —-Non-cyclic Effect (Volts per Metre). 
January. 
February. 
March. 
I April. 
1 May. 
June. 
July. 
August. 
September. 
October. 
November. 
December. 
Year.. 
1898 
+ 17 
- 17 
+ 8 
- 6 
-25 
+ 4 
+ 23 
+ 9 
+ 4 
+ 39 
-22 
+ 1 
+ 3 
1899 
+ 11 
- 4 
-51 
+ 8 
- 12 
+ 14 
+ 12 
-14 
- 8 
+ 18 
+ 8 
+ 30 
+ 1 
1900 
-39 
+ 8 
+ 40 
+ 8 
- 2 
+ 12 
_ 2 
+ 3 
- 4 
+ 9 
+ 11 
+ 29 
+ 6 
1901 
+ 9 
+ 17 
-33 
+ 21 
-22 
- 5 
- 13 
- 2 
- 8 
- 11 
+ 20 
+ 50 
+ 2 
1902 
+ 26 
+ 3 
+ 54 
+ 15 
- 4 
+ 22 
- 1 
- 16 
- 11 
+ 26 
+ 11 
+ 4 
+ 11 
1903 
+ 64 
-23 
- 2 
- 11 
+ 7 
+ 6 
- 6 
-21 
- 12 
-32 
-10 
+ 12 
- 3 
1904 
+ 25 
- 17 
0 
- 9 
- 18 
- 6 
- 18 
- 9 
- 14 
- 18 
-24 
+ 34 
- 6 
Mean 
+ 16 
- 5 
+ 2 
+ 4 
- 11 
+ 7 
- 1 
- 7 
- 8 
+ 4 
- 1 
+ 23 
+ 2 
