40 



Wm. A. Norton on the Variations 



falls steadily until from 5 to 6 a. m. ? (the hour of the second max- 

 imum of horizontal intensity J and after that begins to rise. Thus 

 the one curve has two maxima and two minima, and the other 

 one maximum and one minimum. 2. While the temperature 

 falls in the afternoon and evening as rapidly as it rises in the fore- 

 noon, the horizontal force decreases less rapidly during the for- 

 mer period than it increases during the latter ; and at the same 

 time, as already intimated, the maximum of horizontal intensity 

 frequently occurs an hour or two later than the maximum of tem- 

 perature. 



Figs. 1, 2, 3, 4, 5. 



Curves of the Mean Diurnal Variations of the Horizontal Force for 1844 and the differ- 

 ent quarters of the same year. 



0/* 12345678 9 10 11 12 13 14 15 16 17 18 1920 21 2223 Ok 



^01 



70 



76 



982 



88 

 94 



|M/ 



































i 



1 





















y 

















i 







































— 





































































































































— - 



1000 

































r^ 









06 



1 c\ 















n^ 























12 



1018 



24 



30 



1036 



42 



48 



1054 

 60 

 66 



1072 



78 



84 



1090 



96 



1102 































F 













































































^\ 





















— 



















~b 









































































































c^ 

















^W 

































"+ 





































L 







— — 







































































































































































































^^^*^*^^_ ^^^^^1 "^^^^^ 





1108' 







, 





































I 



II 



HI 



IV 



V. 



0U2 34 5 6 78 9 10 11 12 13 14 15 16 17 18 19 2021 22 23 0A 



I. Jan., Feb. and March. — II. April, May and June. 

 Sept.— -V. Oct., Nov. and Dec. 



Increase of numbers corresponds to decrease of force, 

 scale =-000036 of horizontal force. 



III. 1844.— IV. July, Aug. and 

 One division of Magnetometer 



How are we to account for these discrepancies between the- 

 ory and fact — these deviations of the actual daily variations of 

 the horizontal force from the theoretical variations ? To distin- 

 guish them from those which have just been considered, and 

 which accord with our theory, let us call them the secondary 

 variations of the horizontal force, without meaning thereby to 

 intimate that they are of minor importance. The inevitable in- 



