26 



DISCUSSION OF THE DISTURBANCES 



this table the monthly means and their ratio, when compared with the annual mean, 

 have been added ; also, for comparison, the corresponding ratios found in Part I. of 

 the discussion of the disturbances of the declination. 



In the columns of ratios the principal maxima and minima are indicated by an asterisk. 



The annual means exhibit plainly the eleven year inequality; they have been 

 represented by the formula : 



N = + 14.4 10.2 (t 1843) + 4.8 (t 1843) 2 . 



January, 1841 

 1842 

 1843 



" 1844 

 1845 

 According to the formula, the minimum occurs in January, 1844. 



We have next to consider the eleven year inequality in the magnitude of the 

 disturbances of the horizontal force. Table X. contains the aggregate amount 

 of the disturbances expressed in scale divisions, and also their mean amount obtained 

 by application of the number of disturbances already given in Table VI. 



For reasons already explained, the amount of disturbances in July, 1840, equal 

 to 10761 scale divisions, has been diminished in the ratio of 165 : 63. The ratio of 

 each monthly mean to the mean amount of the year is also given, together with a 

 column of corresponding ratios derived from the disturbances of the declination, as 

 made out in Part I. of the discussion. 



