26 



DISCUSSION OF THE VERTICAL FORCE. 



between 1 A. M. and noon, with an amplitude of about 1.6 scale division (0.00005 

 parts of the force, 0.00067 in absolute measure). The maximum value takes place 

 at. 8 P.M., the same hour at which the horizontal force disturbance is greatest 

 (decreasing that force). 



The disturbance law at Toronto is nearly the same as at Philadelphia, the dis- 

 turbances increase the force between noon and 9 P. M., and decrease it in the 

 remaining hours of the day ; the range at Toronto appears to be larger. 



If we classify the disturbances according to their magnitude in eight groups, 

 each differing 25 scale divisions from the preceding, we find the following scale 

 numbers : 



