58 



DISCUSSION OF THE HORIZONTAL CO 2J PON E N T 



(t,\ Changes of the Horizontal Force feom its Normal Valoe, fob each Roob of the Day ami Month of 



the Year. Expressed in absolute measure. 

 0.00 



January 



February 



- 1 — i i 

 ii" 12 3 4 5 6 



A. M. 



8 10 11 K. 1 2 3 4 5 6 

 P. M. 



7 8 9 10 11 11: 



Philadelphia mean time. 



Annual Variation of Ave 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 tin- value m = + 15.49, 

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

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

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

 the mean for each month, constituting the annual variation. 



