128 
LIEUT.-COLONEL SABINE ON PERIODICAL LAVI^S DISCOVERABLE 
SO generally adopted in the years referred to, that numerical values of this nature, 
derived from a sufficiently extensive induction, should be comparable with each other, 
and should assist in determining the great questions, whether disturbances of the 
class under consideration are wholly general or only partially so ; and whether their 
greater prevalence in particular years, as shown by the observations of any one of the 
observatories, is to be regarded as a general, or as a local, phenomenon. 
If we refer the 1650 disturbed observations to the respective months in which they 
occurred, the numbers are severally as follows ; — 
Table I. 
January 
87 
July 
173 
February 
101 
August 
199 
March 
123 
September 
232 
April 
182 
October 
146 
May 
130 
November 
103 
June 
87 
December 
97 
There are two minima, January and June ; the numbers increase from the minimum 
in January to a maximum in April, and decrease to the second minimum in June; 
they then increase again to a second maximum in September, followed by a decrease 
to the minimum in January. The September maximum is greater than the April 
maximum. If the year be divided into six months of summer and six months of winter, 
the six summer months, i.e. April to September inclusive, have 1003 disturbed obser- 
vations ; and the winter months, i. e. October to March inclusive, 657- If the divi- 
sion be into quarters, solstitial and equinoctial, the two equinoctial quarters have 
the higher numbers, but the summer solstitial quarter (390) is very little less than 
the spring equinoctial (406); the principal contrast is between the autumn equi- 
noctial quarter (577), and the winter solstitial (287). 
If we divide the 1650 disturbed observations occurring in the three years into two 
portions, one containing the easterly disturbances, or those of tlie north end of the 
magnet towards the east, and the other containing the westerly disturbances, we find 
the number to be 897 easterly and 753 westerly ; the easterly preponderating in the 
proportion of T19 to 1. 
If we refer the easterly and westerly disturbances separately to the respective 
months of their occurrence, we have the numbers as follows : — 
Table II. 
Months. 
Easterly. 
Westerly. 
Months. 
Easterly. 
Westerly. 
January 
39 
48 
July 
Ill 
62 
February ... 
50 
51 • 
August 
106 
93 
March 
66 
57 
September ... 
132 
100 
April 
102 
80 
October 
74 
72 
May 
67 
63 
November ... 
45 
58 
June 
62 
25 
December ... 
43 
54 
