212 ON DETERMINATIONS OF THE ABSOLUTE VALUE, SECULAR CHANGE, 
Table V. 
Residual quantities. 
Inclination. 
Horizontal force. 
January, mean of 5 years 
-1- {•40 
— •0004 
February, mean of 5 years 
- I - 1-06 
-•0012 
March, mean of 5 years 
— 0-44 
•0000 
April, mean of 5 years 
— 0*58 
— •0010 
May, mean of 4 years 
— 0-38 
+ •0002 
June, mean of 4 years 
— 1-03 
+ •0028 
July, mean of 4 years 
-1-93 
+ •0033 
August, mean of 4 years 
-0-90 
- +-0022 
September, mean of 4 years 
+ 0-13 
-•0009 
October, mean of 4 years 
+ 0*35 
—•0017 
November, mean of 4 years 
+ 0-97 
—•0023 
December, mean of 4 jmars 
- I - 0-60 
—•0002 
When due allowance has been made for the shortness of the period of observation, 
and for the influence of disturbing action, we find in this tabular view a much more 
conclusive indication of the existence of annual variation than we might perhaps have 
been prepared to expect. The inclination is obviously highest in the winter months 
and lowest in the summer months, passing through its mean value about the period 
of the equinoxes. The horizontal force has a corresponding variation, but with 
opposite signs. The occasional irregularities are more marked in the horizontal 
force than in the inclination, and in both they prevail chiefly in the months of spring 
and autumn. It must remain for a separate discussion, to deduce from the great mass 
of facts which have now been collected at Toronto, the numerical conclusions which 
they will afford in regard to the frequency and magnitude of the disturbances in the 
different months of the year ; but antecedently to the certain conclusions to be drawn 
from such numerical values, it is not an improbable supposition, that the months of 
spring and autumn (and notably those of autumn) may prove to be generally the 
most disturbed months, and consequently those of the greatest depression of the 
horizontal force resulting from the disturbances. The irregularities may be expected 
to diminish as the series is extended ; but if they are, in part at least, occasioned by 
actual irregularities in the force itself produced by the disturbances, they may have 
a character of permanency in certain months which no continuation of the series 
would remove, if it should prove that the disturbances prevail more in some months 
than in others, and if their action has on the average a special tendency. 
In commenting on the fortnightly means of the Bifilar observations at Toronto in 
1842*, (in which year the Bifilar observations were suitable for the investigation, 
inasmuch as the scale-reading returned nearly to the same division at the close, as 
that at which it had stood at the commencement, of the year,) I called attention to 
the remarkable feature, indicated by the Bifilar readings, of an excess in the value of 
the horizontal force in the summer months over the other months of the year; and I 
* Toronto Observations, vol. i. p. xxxvii and xxxviii. 
