MAGNETIC INEQUALITY AT HOBAETON. 
Disturbance-variation. — Before, however, we enter on the lunar question, I wish to 
show the accordance of the two classes of the solar-diurnal phenomena at Hobarton with 
the decennial period, as it has been inferred from observations in other parts of the globe ; 
and I shall commence with the disturbance-variation, because it was from this branch of 
the phenomena that the decennial connexion between the solar-magnetic variations and 
those of the solar spots was first inferred ; and because, on account of the labour which 
is requii’ed in the investigation, the periodical laws of the disturbances have hitherto 
been made out at no other observatories than those of the British Colonies. I gladly 
avail myself therefore of the opportunity of showing, that when the disturbances, occurring 
at Hobarton during eight years, are broken into four distinct and equal portions, each of 
two years’ dmution, each such portion manifests, under a suitable mode of investigation, 
the same periodical law of dimmal variation, almost identical in the principal features of 
direction and turning hom’S, and differing only in the magnitude of the variation in 
different years, in which difference it conforms strictly to the decennial period as indi- 
cated elsewhere, ha\Tng a minimum in 1843 — 1844, and a maximum five years later. 
As the existence of a law of dimmal variation regulating: the occurrence of the disturb- 
ances of large amount rests hitherto, I beheve, only on investigations made by myself, I 
may be excused for here caUing attention to the fact, that each of the foiu’ portions, into 
which the disturbances at Hobarton have been divided, bears its testimony to the existence 
of this law ; — which may be accounted a general one, since it has been found to prevail 
at stations so widely distant from each other as Toronto, St. Helena, and Hobarton. 
The following Table exhibits, for each of the two-yearly periods, the excess at the 
several hours of mean solar time at the station, of the aggregate easterly differences from 
the monthly normal at the same horn- over the aggregate westerly differences (or westerly 
over easterly as the case may be), divided by the number of days of observation in each 
two-yearly period : it is therefore strictly a table of the mean diurnal variation due to the 
disturbances that have been separated for the purpose of investigating the periodical laws 
of this class of the phenomena. 
Table I. 
Hours. 
1841 
and 
1842. 
1843 
and 
1844. 
1845 
and 
1846. . 
1847 
and 
1848. 
Hours. 
1841 
and 
1842. 
1843 
and 
1844. 
1845 
and 
1846. 
1847 
and 
1848. 
Noon. 
0-00 
+ 6-03 
+ 6-10 
+ 6-09 
12 
-6-53 
— 6-38 
-6-45 
— 0'63 
1 
+ 
O-IO 
+ 0*11 
+ 0-08 
+ 0-03 
13 
— 0*30 
— 0-23 
-0*39 
— 0-54 
2 
0-00 
+ 0-11 
+ 0-03 
— 0-02 
14 
— 0-20 
— 0-14 
-0-35 
-0-36 
3 
0-05 
+ 0-12 
+ 0-07 
+ 0-20 
15 
— 0-17 
-0-05 
-0-19 
-0-33 
4 
+ 
0*15 
+ 0-06 
+ 0-07 
+ 0-23 
16 
+ 0-05 
+ 0-03 
-0-03 
-0-28 
5 
+ 
0-13 
+ 0-03 
+ 0-03 
+ 0-32 
17 
+ 0-08 
+ 0-09 
+ 0-01 
J-0'03 
6 
— 
0-04 
-0-05 
-0-05 
+ 0-20 
18 
+ 0-13 
+ 0-09 
+ 0-04 
+ 0-10 
7 
— 
0*17 
— 0-17 
— 0-11 
— 0-10 
19 
+ 0-20 
+ 0-09 
+ 0-17 
+ 0-22 
8 
— 
0-43 
-0*30 
— 0-22 
-0-26 
20 
+ 0-27 
+ 0-11 
+ 0-10 
+ 0-23 
9 
— 
0-42 
-0-43 
-0-37 
-0-39 
21 
+ 0-14 
+ 0-06 
+ 0-15 
+ 0-10 
10 
— 
0-55 
-0-36 
-0-41 
— 0-64 
22 
+ 0-05 
+ 0-06 
+ 009 
+ 0-19 
11 
0-59 
— 0-43 
-0-46 
— 0-82 
23 
+ 0-01 
+ 0-05 
+ 0-12 
+ 0-13 
B 2 
