OF THE HORIZONTAL FORCE. 



29 



The average amount of a disturbance increasing the horizontal force is 45 scale 

 divisions, or 0.0069 in absolute measure ; the average amount of a disturbance 

 decreasing the same is 54 scale divisions, or 0.0082 in absolute value. The ratio 

 of these numbers is as 1 : 1.2, whereas at Toronto the ratio is 1 : 6.4. 



The law of the monthly inequality for amount of increasing or decreasing dis- 

 turbances is, as in the preceding case, very indistinct and further obscured by the 

 small absolute amount of variation. 



In the following Table, XIII., the larger disturbances have been distributed 

 over the different hours of their occurrence; in this combination the bi-hourly series 

 (of the even hours) of observation has been used throughout. 



Directing our attention to the columns of aggregate amount and of ratios of 

 number of occurrence, we find a principal maximum about 11 A. M., which seems 

 to correspond to the secondary maximum of corresponding ratios at Toronto occur- 

 ring about three hours earlier; the principal minimum occurs about 5 A. M., which 

 corresponds to the secondary minimum at Toronto occurring between 5 and 6 A. 

 M. ; again, at Philadelphia, the secondary maximum at midnight is about two hours 

 earlier than the principal maximum at Toronto, and the secondary minimum about 



