Chase.] 



162 



[October. 



Taking Toronto as a typical station of average, and St. Helena as 

 one of minimum accidental magnetic disturbance, 1 first deduced 

 from three years' observations at each place (1843, '4, '5 at Toronto; 

 1843, '5, '6 at St. Helena; the observations of 1844 being com- 

 paratively incomplete), the average duration of the fluctuations of 

 each element. I found the following mean lengths of an oscillation, 

 measuring from the maximum of one wave to the maximum of the 

 succeeding wave (B representing the barometer; T, thermometer ; 

 H, horizontal force ; V, vertical force ; T>, declination). 



The mean wave-periods, taking the duration of the alternate varia- 

 tions above and below the monthly means, were as follows : 



By marking with the signs -f and — the excess or deficiency of 

 each daily mean, the monthly mean being assumed as the standard 

 of comparison, I obtained the data for Tables I and II. The columns 

 headed C contain the number of observations that present a corre- 

 spondence (excess in one element accompanying excess in the other, 

 and vice versa), and those headed give the number of instances in 

 which there was an opposition of signs between the daily means in- 

 dicated by the heading of each double column. 



