132 
LIEUT.-COLONEL SABINE ON PERIODICAL LAWS DISCOVERABLE 
direction, of the values of the easterly and westerly disturbances, the general result 
of the disturbances of this class, viz. those of large amount, must be to produce a 
mean diurnal variation of a distinct character from that which is usually known as 
such ; inasmuch as the periodical law indicated by the last Table is very different in 
the hours of easterly and westerly deflection, and in those of maxima and minima, or 
the turning-points, from the law of the diurnal variation derived from the whole body 
of the observations. The correct inference will then be, that the larger disturbances 
have a periodical law of their own, regulating their mean effects, and influential on 
the mean direction of the magnet at different hours of the twenty-four; and that this 
law is not the same as the periodical law derived from the other observations from 
which they have been separated. For the purpose of examining this question, which, 
for the reason already stated, requires that the mean numerical values of the larger 
disturbances at the several hours should be sought out, I have had the mean diurnal 
variation for the years 1843, 1844 and 1845 at Toronto computed in two different 
ways, viz. — 1st, from the whole body of the hourly observations, no observation what- 
soever being omitted; 2nd, from the same observations, omitting the 1650 disturb- 
ances of largest amount separated in the manner described in this paper ; that is to 
say, from the 20,726 remaining observations. In the difference between the two we 
have the mean diurnal variation produced by the larger disturbances, estimated on 
the average of the whole period of three years : it is shown in the following Table: — 
Table VII. 
Hours of 
Toronto time. 
Mean diurnal variation 
produced by the larger 
disturbances. 
Hours of 
Toronto time. 
Mean diurnal variation 
produced by the larger 
disturbances. 
6 A.M 
0*02 West. 
6 P.M 
0*1 6 East. 
7 A.M 
0*02 West. 
7 P.M 
0*28 East. 
8 A.M 
0*10 West. 
8 P.M 
0-56 East. 
9 A.M 
0*09 West. 
9 P.M 
0’79 East. 
10 A.M 
0‘06 West. 
10 P.M 
0‘73 East. 
11 A.M 
O'Ol East. 
11 P.M 
0‘42 East. 
Noon 
0*09 West. 
Midnight ... 
0*36 East. 
1 P.M 
0-02 West. 
1 A.M 
0’33 East. 
2 P.M 
0’04 West. 
2 A.M 
0‘20 East. 
3 P.M 
0'08 West. 
3 A.M 
0-14 East. 
4 P.M 
0‘03 West. 
4 A.M 
0‘03 East. 
5 P.M 
0'03 East. 
5 A.M 
0*00 
A glance at this Table is sufficient to show that the periodical law which governs 
the larger disturbances is quite as clearly manifested, and its systematic character as 
clearly evidenced, when their mean numerical values are substituted for the numbers 
of easterly or westerly disturbances occurring at the different hours. It will be best 
to reserve any further comments until the results have been stated of a similar exami- 
nation of the observations at the Hobarton observatory in the same three years, 1843, 
1844 and 1845. 
