OF THE DIP. 



21 



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

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



(B). SOLAE-DIURNAL VaEIATION OP THE MAGNETIC DiP APRIL TO SEPTEMBER, 1841 1845. 



(Expressed in minutes.) 



Off 



'■3 I 



.6 

 .4 

 .2 

 .0 

 .2 



+1.0 

 .8 

 .6 

 .4 

 .2 

 .0 

 .2 

 .4 



— .6 



+1.0 

 .8 

 .6 

 .4 

 .2 

 

 .2 

 .4 

 .6 



1 I 1 1 1 



r 



/• 



\ \ \ \ \ ■ 



\ 



v.. 



i 1 1 1 1 



; '^'"^r^ 



/ 



V 



X. ,- 



'-----■ 



/ 



\ 



\ 



: /-^-y 





\ 





: ./ 



^ „ ■ 



\ 1 

 In. 



\ 



\_.- 



; ..^■^■.^ 



' 1 



1 



\ 



\_,: 



1 1 1 t 1 



1 



1 1 1 I I 



1(111 



\ - 



r 1 1 1 1 



April 



May 



+1.'0 

 .8 

 .6 

 .4 

 .2 

 

 .2 

 .4 



— .6 



+ -8 

 .6 

 .4 

 .2 

 

 ■2 

 .4 



— .6 



July +1.0 

 .8 

 .6 

 .4 

 .2 



August 



.2 



.4 



— .6 



September 



0" 2 4 6 8 10 



14 16 18 20 22 24" 



Philadelphia mean time. 



