OF THE MAGNETIC FORCE. 



19 



mean (the monthly mean for the respective hour), also the number of observations 

 in each year subjected to the process: 



LIMITS OF REJECTION BY PEIRCE'S CRITERION. 

 Div's. 



1840-41 ex = 53 ?i = 241 



1841-42 " 44 312 



1842-43 " 37 309 



1843-44 28 313 



1844-45 " 33 313 



Mean value 39 Sum 1488 



The limiting value derived from nearly 1,500 observations is 39 scale divisions, 

 and the separate annual values show plainly the effect of the eleven (ten 1) year 

 period, the year 1843-4 being a minimum year. Certain limits in the adoption of 

 a separating value are allowable, and upon trial as to the actual number of disturb- 

 ances separated, the value 33 scale divisions was finally adopted. Any observation 

 differing 33 divisions or more from its respective monthly mean, was therefore 

 marked and excluded from the mean. 33 divisions equal 0.0012 parts of the hori- 

 zontal force, and in the value of the absolute scale it amounts to 0.005. At Toronto 

 the limiting value was 14 divisions, = 0.0012 parts of the horizontal force, equal 

 to 0.004 in the absolute scale. (Vol. Ill of the Toronto Obser's.) 



Total number of observations 

 Total number of disturbances 



24,231 

 1,698 



The limiting value separated, therefore, one in every 14.3 observations. 

 Toronto one in every 12.5 was marked as a disturbance. 



At 



1 In 17 days. 

 1 In 19 days. 



' One observation a day. 

 One observation a day. 



* One observation a day. 



