A. D. Bache on the Horizontal Component of Magnetic Force. 267 



According to the formula, the minimum occurs in January, 

 lS4i. 



We have next to consider the eleven year inequality in the 

 magnitude of the disturbances of the horizontal tbrce. Table 

 No. X contains the aggregate amount of the disturbances, ex- 

 pressed ia scale divisions, and also their mean amount obtained 

 h 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 de- 

 clination as made out in part I. of the discussion. 



s No. X,— Aggregate and mean a 





force 



erpye^di^S. 



ale div 



hions. 









HO.TH. 



1840411 184^2 



IS4243 



184344 



184445 



Mean 





""':::: 



Anilxst, 



^ffife" 



"^? 



669 



T42 



5a 



!-o3 



o;87 







is^ 



239 



'S 



i;i 



i 



;:i 





J.n„„y, ■ 











,402 









_Meati^mount, 



2664 



1 

 53:?- 





1 



I187 



J6T 



i 



49 



:|* 



o^l 



Maxima and minima in the columns 

 sn asterisk. 



, The inequality in the mean amount .q,o aa 



disturbances in each year, indicates the year 1843-44 



marked with 

 of the horizontal force 



th of No 

 minimum of the elevi 



From the preceding results, ^ 

 vember, 1843 as the epoch for tue imui.w.^." -.-.-- - v 



year?) inequllfty, as far as indicated by the differential obsei 

 Nations of the horizontal force. 



Further Analysis of the Disturbances of the ffoAzontal Force. 



The distribution of the disturbances in ^.^"^^^^^^''^. °L^^i^ 

 atnount over the several months of the year has been given m 



From'table IX we learn that the disturbances are greatest in 

 dumber in September and March, or April, or about ^^e time 01 

 tl^e equinoxes^ and least in number about January and J an ^'^^ 

 about the time of the solstices. At the autumnal equinox the 



