DISCUSSION OF THE VERTICAL FORCE. 



25 



Average magnitude 43 scale divisions, the disturbances appear to be nearly of 

 the same size at all hours, there is a slight preponderance in magnitude between 

 10 A. M. and 10 P. M. over the other half of the day. 



The magnitude of the disturbances, either increasing or decreasing the force, 

 apparently does not vary with the hours of the day. The disturbances which 

 increase the force preponderate between the hours 2 P. M. and 2 A. M. ; those 

 which decrease the same occur in the other half of the day, the average ratio of 

 the preponderance of increase over decrease is as 4 to 1. 



Dividing the numbers in the last column of the preceding table, or the excess 

 of the sum of disturbances increasing the force over the sum of those decreasing 

 the same, by the total number of days (1297) of observation, we find the diurnal 

 disturbance variation as follows : 



The value for the hour 14 is evidently anomalous, the mean of the hours 12 and 

 16 or + O d .2 (0.00001 in parts of force, 0.00008 in absolute measure) should be 

 substituted. The average daily effect of the larger disturbances is therefore to 

 increase the vertical force between 1 P. M. and midnight, and to decrease it 



