OF THE DIP. 



Diagram (B) exhibits the observed and computed diurnal variation for 

 mer months, and diagram (C) for the winter months. 



21 



the sum- 



(B). SOLAR-DIURNAL VARIATION OF THE MAGNETIC DlP APRIL TO SEPTEMBER, 1841 1845. 



(Expressed in minutes.) 



if 



a I 



8 



+ -'8 

 .6 

 .4 

 .2 

 .0 

 .2 

 .4 



.6 



+1.0 

 .8 

 .6 

 .4 

 .2 

 .0 

 .2 

 .4 



.6 



+1.0 

 .8 

 .6 

 .4 

 .2 

 

 .2 

 .4 

 .6 



.8 



i i I i i 



\ 





\ 



\ 



! ( t 1 t 





\ 



N 



\ 



I 1 t t 



April 



May 



June 



.8 

 .6 

 .4 

 .2 

 

 .2 

 .4 

 .0 



+ -8 

 .6 

 .4 

 .2 

 

 .2 

 .4 



.6 



July +1 



August 



September 





 % 



o 



0" 



6 8 10 



g 



14 16 18 20 22 24 11 



Philadelphia mean time. 



