IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 367 
Table III. 
Toronto Astro- 
nomical Hours. 
Declination. 
Horizontal 
Force. 
Vertical 
Force. 
Toronto Civil 
Hours. 
18 
1-05 
1-00 
1-21 
6 A.M. 
19 
M7 
1-40 
M5 
7 A.M. 
20 
1-27 
1*20 
0-80 
8 A.M. 
21 
1-11 
1-00 
0-54 
9 a.m. 
22 
0-87 
1-00 
0-36 
10 A.M. 
23 
0-66 
0-90 
0-34 
1 1 A.M. 
0 
0-49 
0*87 
0-46 
Noon. 
1 
0-30 
0-76 
0-63 
1 P.M. 
2 
0-40 
0-66 
0-77 
2 P.M. 
3 
0-40 
0-66 
0-87 
3 P.M. 
4 
0*33 
0-61 
1-04 
4 P.M. 
5 
0-56 
0-66 
1-07 
5 P.M. 
6 
0-84 
0-59 
1-01 
6 P.M. 
7 
0-98 
0-76 
1-05 
7 P.M. 
8 
1-22 
0-75 
0-89 
8 P.M. 
9 
1-82 
0-90 
0-74 
9 P.M. 
10 
1-55 
1-03 
0*85 
10 P.M. 
11 
1-25 
1-14 
0-93 
11 P.M. 
12 
1-35 
1*22 
1*39 
Midnight. 
13 
1-52 
1-58 
1-58 
1 A.M. 
14 
1-21 
1-60 
1-61 
2 A.M. 
15 
1-13 
1-37 
1-73 
3 A.M. 
16 
1-34 
1-14 
1-51 
4 A.M. 
17 
1-05 
1*02 
1-41 
5 A.M. 
From the systematic increase and decrease of the ratios at the different hours, 
it is obvious that the disturbances of each element, when viewed on the average of a 
sufficient body of observations, are regulated by laws which have a diurnal period. 
The diurnal variation thus presented is far however from being alike in each of the 
three elements ; the maximum disturbance takes place indeed in all the elements 
during the hours of the night, and the minimum disturbance during the hours of the 
day ; but the particular hours of maximum and minimum are very different in the 
three cases. The hour of maximum in the Declination, for example, is 9 p.m. when 
the disturbances of the horizontal and vertical forces are both even less than the 
hourly average’, and the horizontal and vertical forces do not reach their hours of 
maximum until, respectively, 2 and 3 a.m., when the disturbances of the Declination 
iiave notably declined. So in respect to the hour of minimum : that of the Declina- 
tion, 1 P.M., is nearly midway between that of the vertical force at 11 a.m., and that 
of the horizontal force at 4 p.m. ; the disturbance of the horizontal force being still 
high when that of the vertical force is at a minimum, and the disturbance of the ver- 
tical force being still high when that of the horizontal force is a minimum. Speaking 
generally, the disturbances of the three elements are above the average in the hours 
of the night and early morning, and below the average during the hours of the day; 
to the latter, however, there is an exception in the vertical force, which is above the 
average from 4 to 7 p-m. In the Declination the aggregate value of the disturbances 
at the hour of maximum is about six times as great as at the hour of minimum; in 
3 c 2 
