DISCUSSION OF THE HORIZON T A L C O M P O N H N T 



I OF T11E IIoEIZOXTAL FORCE FROM ITS NoKMAL VALUE, FOR EACU Hoi'K Of THE L>AY AM) MoliTU OF 



TUB YICAK. Expressed iu absolute measure. 

 0.00 



(II. 



123 

 A. M. 



4567 



10 11 N. 1 2 3 4 5 

 P.M. 



Philadelphia mean time. 



6 7 8 9 10 11 12" 



Annual Variation of tfte Horizontal Force. For the discussion of the annual 

 variation we make use of the monthly normal readings of the horizontal force as 

 given in Table II. If m equals the monthly effect of the total progressive change, 

 we obtain from the twelve equations by the usual method the value m = + 15.49, 

 and the correction for progressive change for July and June, for instance, becomes 

 + 5.5 m and 5.5 in respectively. The following table contains the monthly 

 normals unconnected and corrected for progressive change; also the differences from 

 the mean for each month, constituting the annual variation. 



