52 



DISCUSSION OF THE VERTICAL COMPONENT 



DIAGRAM (F). 



0" 2 4 6 8" A. M. 

 Philadelphia mean time. 



Table VII exhibits the computed times of the principal maximum and minimum 

 of the vertical force, together with the amount of difference from its average daily 

 value at these epochs, expressed in scale divisions ; also the time and amount of 

 the early morning secondary fluctuation traceable only in the winter months ; for 

 these last values the diagrams have been made use of. 



The extreme variation in the time of the maximum in the course of a year is 

 3 h 18 m , and of the minimum 4 h 11'". 



At Toronto the occurrence of the maxima and minima is later than at Phila- 



