DISCUSSION OF THE VERTICAL FORCE. 



21 



ratios, it is probably due to the small number of observations, and the difficulty in 

 keeping the instrument in adjustment and allowing for its irregularities. I have, 

 therefore, given the mean ratio of the Philadelphia disturbances in the last column 

 of Table VII, and compared the result, graphically, with those deduced by General 

 Sabine for Toronto. 1 



ANNUAL INEQUALITY OP DISTURBANCES. 



If we separate the disturbances into two parts, those increasing and those 

 decreasing the force, we obtain the numbers of Table VIII. A positive sign indi- 

 cates disturbances increasing, a negative sign those decreasing the vertical force. 

 The law of the annual variation seems to be the same as shown by the ratios in the 

 last two columns ; this accords with the result at Toronto. 



Page Ixx., Vol. III. 



