28 



SOLAR DIURNAL VARIATION 



Dia"-ram (F) exhibits the observed and computed diurnal variation for the sum- 

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



(F). SOLAK-DlURNAL VARIATION OF TOE MAGNETIC TOTAL PORCE ArRIL TO SEPTEMBER, 1841 1845. 



(Expressed in parts of the force.) 



Philadelphia mean time. 



