DR. EVERETT ON ATMOSPHERIC ELECTRICITY. 
;55 
order of date, and from these entries the results shown in the subjoined Tables were 
computed. 
Table I. shows the mean electrical potential for each day, omitting those days on which 
the number of blanks exceeded two. 
Table II. shows the mean electrical potential for each of the twenty-four hours, month 
by month, and the last line and column contain the means of the other lines and columns 
respectively. 
From the numbers in the body of this Table the curves (Plate XX.) have been drawn, 
the first twelve lines of numbers being represented by the continuous curves, and the 
next twelve lines by the dotted curves. These curves very clearly show a double maxi- 
mum and minimum, the principal maximum occurring about 8 p.m. in autumn and 
winter, 9 p.m. in spring, and 10 p.m. in summer, and the secondary maximum about 
8 a.m. in spring and summer and 9 a.m. in autumn. The principal minimum occurs 
at 4 a.m. in spring and summer and 5 a.m. in autumn and winter. The curvature is 
greater in the neighbourhood of the maxima than in the neighbourhood of the minima. 
The mean diurnal curve at Kew (Plate XXI.) has been drawn by projecting the 
numbers in the last line of the Table, the vertical scale adopted being twice as large as 
for the twenty-four curves belonging to single months. Above this is placed the diurnal 
barometric curve for Plalle, drawn from data contained in Kaemtz’s ‘ Meteorology,’ and 
below is placed the diurnal electrical curve for Windsor, N.S., obtained by taking the 
gross means of my own observations at each hour, observations from 2 to 6 a.m. being 
entirely wanting*. The electrical curves for the two places are remarkably dissimilar, 
both, however, having a maximum between 8 and 9 A.M.f The principal maximum at 
Kew occurs between 8 and 9 p.m., and the principal minimum between 4 and 5 A.M. 
The barometric curve for Halle bears a strong resemblance to the Kew electrical curve, 
but is upwards of an hour later in phase. The slight rise in the Kew curve at 11 a.m. 
is attributable to the fact that the Leyden jar was recharged at 10.30 a.m. By project- 
ing the numbers in the last column of the Table, we obtain annual curves of electricity 
for two years. I have projected these so as to form one continuous curve, and along 
* These means, together with the number of observations from which they are deduced, are as follows, in 
units of “ station electrometer with second fibre.” 
Hour 
17 to 19 
19 to 20 
20 to 21 
21 to 22 
22 to 23 
23 toO 
0to 1 
Number of observations . . 
7 
114 
227 
103 
43 
30 
32 
Mean 
3-17 
3-93 
4-51 
4-23 
3-32 
3-29 
3-90 
Hour 
1 to 2 
2 to 3 
3 to 4 
4 to 5 
5 to 6 
6 to 7 
7 to 8 
Number of observations . . 
155 
223 
35 
53 
45 
38 
26 
Mean 
4-44 
4-53 
3-67 
3-84 
3-76 
3-73 
3-44 
Hour 
8 to 9 
9 to 10 
10 to 11 
11 to 12 
12 to 14 
Number of observations . . 
34 
272 
68 
32 
8 
Mean 
3-18 
3-28 
2-71 
2-97 
2-81 
f At Windsor, in every month without exception, electricity wgs weaker at 10 p.m. than either at 9 a.m. or 
2 p.m., hut the reverse of this rule would appear to hold at Kew. 
MDCCCLXY1II. 3 D 
