IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 117 
Table XVI. — Mean monthly diurnal range of the Declination at Hobarton. 
Years. 
Winter. 
Spring and Autumn. 
Summer. 
Mean of the 
whole year. 
May, June, 
July, August. 
September, October, 
March, April. 
November, December, 
January, February. 
1843 
4-50 
7*80 
10-16 
7-66 
1844 
4-30 
8-45 
10-77 
7-84 
1845 
4-39 
8-61 
12-16 
8-39 
1846 
5-10 
9-50 
12-58 
9-06 
1847 
5-38 
10-97 
13-43 
9-93 
1848 
7-09 
10-67 
14-14 
10-63 
We perceive by Tables XV. and XVI. that a generally and almost uniformly pro- 
gressive increase took place at Toronto and Hobarton in the mean monthly range 
of the diurnal variation of the Declination between 1843 and 1848, contemporaneously 
with the increase in the amount of the disturbances produced by the variations which 
are of less regular occurrence and have distinct phenomenal laws. This coincidence 
appears to afford a more direct and decided indication of a causal connection sub- 
sisting between the two classes of phenomena than any which has previously pre- 
sented itself. 
It might be supposed that an increased amount of disturbance occurring in any 
year from the last named causes, i. e. the disturbances, might have a direct effect in 
increasing the diurnal range of the Declination ; and such undoubtedly must be the 
case on individual days ; but when mean values are in question, as is the case here, 
the difference in the mean monthly diurnal range, when the disturbed observations 
are retained, or when they are omitted, is scarcely sensible. The following Table 
contains the mean monthly diurnal range in the different years at Hobarton, when 
the 3469 disturbances of largest amount have been withdrawn. When compared 
with the values in Table XVI., where the disturbances are retained, the difference is 
seen to be wholly insignificant. 
Table XVII. — Mean monthly diurnal range of the Declination at Hobarton, the 
3469 disturbances of largest amount being omitted. 
Years. 
Winter. 
Spring and Autumn. 
Summer. 
Mean of the 
whole year. 
May, June, 
July, August. 
March, April, 
September, October. 
November, December, 
January, February. 
1843 
4-49 
7-80 
10-67 
7-65 
1844 
4-19 
8-29 
10-62 
7-70 
1845 
4-37 
* 8-57 
12-13 
8-36 
1846 
4-59 
9*26 
12-76 
8-87 
1847 
5-18 
10-50 
13-80 
9-83 
1848 
7-02 
10-53 
14-19 
10-58 
Facts so remarkable as those presented in Tables XV. and XVI., showing in the 
course of six years a progressive increase in the range of the diurnal variation taken 
