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



which corresponds to the secondary minimum at Toronto, oc- 

 curring between 5 and 6 a. M. ; again at Philadelphia the sec- 

 ondary maximum at midnight is about two hours earlier than 

 t\ie principal maximum at Toronto, and the secondary minimum 

 about 4 p. M. corresponds in time to the principal minimum at 

 Toronto, occurring between 2 and 6 P. M. Thus the curves at 

 the two stations representing the diurnal variation of the dis- 

 turbances (irrespective of increase or decrease) of the horizontal 

 force is double crested with an exchange of the principal and 

 secondary maximum and also of the principal and secondary 

 minimum. 



In the next table, No. XIV, the diurnal variation of the dis- 

 turbances is exhibited separately, for disturbances increasing. ; 

 ! decreasing -the horizontal force. 



„„,. 



■f 



'\sr 



k1. 



:r 



^V^ 



'\.Uo. 



SB.. 



o midnight, 



57 

 48 



i 



2878 



?758 

 "96 



I39 



i 



85 



87 



11 



87 



'89 



1? 

 5065 



i 



0-74 



ii 



1 



Sums, 



5S5 



.697. 



I300 



936 



52028 



1100 



_j5o57__ 



The disturbances increasing and those decreasing the honzou- 

 tal force evidently follow different laws ; at Toronto they were 

 found completely opposed; they are less so at Philadelphia. 

 The principal maximum of increasing disturbances (at noon) 

 seems to be cotemporaneous with a secondary minimum ot th 

 decreasing disturbances; again the principal maximum ot ttie 

 decreasing disturbances (at 8 p. m.) corresponds to a seconaary 

 minimum of the increasing disturbances. In reference to tft 

 main feature, the maximum disturbance of those increasing tne 

 force and of those decreasing the force, the Philadelphia ratios 

 show even a greater resemblance to the results at St. Helena 

 and the Cape of Good Hope than to those at Toronto. At pe 

 two southern stations, the maximum in the disturbances whica 

 increase occurs at 11 a.m., and the maximum in the <iist"^% 

 ances which decrease occurs about 6 or 7 P. M. (See vol. Uj " 

 the St. Helena Observations.) 



Table XIV contains also the hourly excess of the aggregate 

 amount of the disturbances which decrease the horizontal iorce 

 over those which increase the same. K we divide the nambers 



