DISCUSSION OF THE VERTICAL FORCE. 



23 



1841, to June, 1845, omitting only the single daily observation in January, Febru- 

 ary, and March, 1843. Strictly speaking the time is 21 minutes later than indicated 

 in the table. 



The greatest number of disturbances occur about A. M. (at Toronto at 3 A. M.), 

 with the least number at 10 A. M. (at Toronto at 11 A. M.); the secondary maxi- 

 mum and minimum occur about 2 P. M. and 7 P. M. (at Toronto the hours are 5 

 P. M. and 9 P. \L). On the average, therefore, the maxima and minima occur l h 

 40 m earlier at Philadelphia than at Toronto. At neither station do the three ele- 

 ments show the same law; they agree only in so far as to exhibit a systematic in- 

 crease and decrease with the solar hours, and in having two maxima and two minima. 



The diagram shows the law of the disturbances of the vertical force for Phila- 

 delphia and Toronto. 



DIURNAL VARIATION OF DISTURBANCES. 



