230 AURORA BORE ALLS. 



and 91 per cent, ended with northerly force — . The disturbance in a vertical 

 direction was sometimes positive and sometimes negative, with about equal fre- 

 quency. 



The following table presents a summary of the results for twenty cases of the 

 most remarkable disturbance, including all the cases in which the mean dis- 

 turbance of the declination magnet amounted to fourteen minutes. In the 

 column headed " declination magnet," the plus sign shows when the western 

 declination was greater than the mean, and the minus sign when it wa^ less 

 than the mean. In the two columns headed " horizontal force" and " vertical 

 force magnet," the plus sign shows when the force was greater than the mean, 

 and the minus sign when it was less than the mean. 



In order to reduce the table to convenient limits, the numerical values of 

 several of the changes are not given ; but the direction and number of the 

 changes are indicated by the repetition of the signs +, — , -}-, etc. 





