14 



DISCUSSION OF THE DISTURBANCES 



year period as plainly and systematically as did the investigation of the diurnal 

 amplitude ; yet giving half weight, on account of the want of record, to the sums 

 for 1840 and 1845, the minimum number falls in the year 1843. More consistent 

 results would, no doubt, have been obtained if the year 1845 had been complete. 



If we distribute the disturbances (1942 in number for the even hours) according 

 to their respective hours of occurrence, the following table results from observa- 

 tions between 1840 and 1845: 



Maxima and minima values are distinguished by an asterisk. 



The numbers in each vertical column show a regular progression ; and the number 

 of disturbances, irrespective of their direction, have a minimum at 2 P. M. and a 

 maximum at 2 A. M. 1 The principal contrast is between the hours of the day and 

 the hours of the night ; in the former case the numbers being below, but in the 

 latter above the mean value. This is in close correspondence with the Toronto 

 results. The most striking result of the above table is that the westerly disturb- 

 ances have their minimum precisely at the hour (8 P. M.) when the easterly have 

 their maximum value ; and the exact coincidence of this result with that deduced 

 by General Sabine for Toronto is not less remarkable. For the westerly disturb- 

 ances, the hours 6 A. M. (maximum) and 8 P. M. (minimum), and for the easterly 

 disturbances the hours 2 P. M. (minimum) and 8 P. M. (maximum), are specially 

 contrasted. These results also agree with those found at Toronto ; and the accord- 

 ance with that station even goes so far as to exhibit the secondary minimum of 

 eastern disturbances at 8 A. M. In connection with this subject it may be here 

 stated, that the same distinguished magnetist found a singular mutual relation to 

 subsist between the phenomena at Toronto and Point Barrow, on the shores of the 

 Arctic Sea the laws of the easterly deflection at one station being found to cor- 

 respond for the same local hours, with those of the westerly deflections at the other 

 station, and vice versd. This contrast holds good for Philadelphia as well as for 

 Toronto. 



We now pass to the consideration of the amount of deflections caused by the 

 disturbances, classifying the same according to years, months, and hours : 



At Toronto the respective honrs are 2 P. M. and 22 P. M. 



