50 



DISCUSSION OF THE DIURNAL VARIATION 



The following comparison will show the agreement of the observed and computed 

 values we have for August: — 



Diagrams C and D exhibit the regular solar-diurnal variation of the horizontal 

 force; the dots represent the observations directly taken from Table 1; the curves 

 give the computed values from tbe preceding equations. These diagrams also 

 exhibit the general agreement between the observed and computed values. The 

 summer months arc represented on diagram C, the winter months on diagram D; 

 their comparison shows plainly the much greater range of the diurnal variation 

 when the sun is north of the equator than when south of it, as was also the case 

 with the magnetic declination. 



