28 



SOLAR DIURNAL VARIATION 



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

 mer months, and diagram (G) for the winter mouths. 



(F). SOLAR-DlURNAL VARIATION OP THE MAGNETIC TOTAL FORCE APRIL TO SEPTEMBER, 1841 1845. 



(Expressed in parts of the force.) 



o 







+.000400 



300 



200 



100 







100 

 200 

 300 



.000400 



+.000400 



300 



200 



100 







100 

 200 

 300 



.000400 



+.000400 



300 



200 



100 







100 

 200 

 300 



.000400 



i i i i i 



April 



May 



June 



July + 



August 



Septemb. 



4 

 g 



a 



"a 

 3 



..000400 



300 



200 



100 







100 

 200 

 300 



-.000400 



.000400 



300 



200 



100 







100 



200 



300 



..000400 



000500 

 400 

 300 

 200 

 100 

 



100 

 200 

 300 

 400 



000500 



0" 2 



6 8 10 



a 

 I 



14 1C 18 20 22 24" 



Philadelphia mean time. 



