358 
DR. EYEEETT ON ATMOSPHERIC ELECTRICITY. 
Two years combined. 
Ai. 
Ei- 
Hour of 
maximum 
from E r 
a 2 . 
e 2 . 
Hours of maxima 
from E 2 . 
h 
m 
h 
m 
h 
m 
June 
•232- 
-50 
4 
9 
20 
•292 
+ 190 
3 
8 
40 
20 
40 
July 
•140 
-92 
27 
12 
10 
•395 
166 
40 
9 
27 
21 
27 
August 
•111 
-30 
15 
8 
1 
•398 
177 
59 
9 
4 
21 
4 
September 
•477 
-34 
30 
8 
18 
•483 
187 
1 
8 
46 
20 
46 
October 
•720 
+ 9 
16 
5 
23 
•339 
202 
24 
8 
15 
20 
15 
November 
•454 
- 9 
46 
6 
39 
•310 
199 
6 
8 
22 
20 
22 
December 
•877 
+ 10 
39 
5 
17 
•507 
184 
14 
8 
52 
20 
52 
January 
M74 
+ 7 
9 
5 
31 
•389 
194 
45 
8 
30 
20 
30 
February 
•689 
- 5 
25 
6 
22 
•587 
193 
18 
8 
33 
20 
33 
March 
•279 
-36 
15 
8 
25 
•558 
194 
7 
8 
32 
20 
32 
April 
•398 
-62 
28 
10 
10 
•508 
196 
9 
8 
28 
20 
28 
May 
•331 
-85 
40 
11 
43 
•259 
177 
34 
9 
5 
21 
5 
Year 
•424 
-13 
50 
6 
55 
•413 
189 
0 
8 
42 
20 
42 
The term involving and takes one maximum in the twenty-four hours, whose 
times are given in the third column of the above Table. The term involving A 2 and E 2 
takes two maxima which are always twelve hours apart. Their times are given in the 
last two columns. In deducing the hours of maxima from the values of E x and E 2 , it is 
to be borne in mind that the phases are earlier in proportion as the epochs are greater, 
15° in the value of Ej and 30° in the value of E 2 corresponding respectively to differences 
of an hour. It will be observed that the earliest and latest hours of maxima differ by 
about seven hours in the case of E„ and by only one hour twelve minutes in the case of E 2 . 
The values in the last line of the Table are derivable either from the last line of 
Table II. or from the means of the values of P n Q,, P 2 , Q 2 . The amplitudes of the 
diurnal and semidiurnal terms are, it will be seen, nearly equal. Practically, the hours 
of electrical maxima month by month agree, within an hour or two, with those of the 
semidiurnal term, and the hourly values for the average of the year, given in the last 
line of Table II., show a still closer agreement. The diurnal term, without having much 
effect on the times of maxima, causes one maximum to be much greater than the other. 
It may be interesting to inquire into the connexion, if any, between electrical and 
barometrical maxima, an inquiry which is suggested by the fact that the latter, like the 
former, occur twice in the twenty-four hours. In default of the necessary barometric 
data for Kew, I have compared the numbers in the last line of Table II. with the fol- 
lowing numbers which represent the mean heights of the barometer at Halle for all 
hours on the average of the whole year, and are taken from Kaemtz’s ‘ Meteorology,’ 
page 248. 
Barometric Heights at Halle (lat. 54° 29'), in millimetres, 
750 plus the following numbers. 
Noon. 
3-29 
l h . 
3-11 
2 h . 
2-99 
3 h . 
2-89 
4*. 
2-84 
5 h . 
2-86 
6 h . 
2-91 
3-02 
8 h . 
3-14 
9 h . 
3-24 
^ CO 
li h . 
3-29 
12 h . 
3-23 
13 h . 
3-14 
14 h . 
3*05 
15 h . 
2-99 
16 h . 
2-99 
17 h . 
3-34 
18 h . 
3-12 
19». 
3-24 
20 h . 
3-37 
21 h . 
3-44 
22 h . 
3-46 
23 h . 
3-40 
