4 ANALYSIS OF THE 



respective force. These disturbances of the two components were tabulated in 

 chronological order, and when, for any entry, but one of the constituent parts 

 appeared disturbed, the corresponding difference from the normal of the contempo- 

 raneous second part, whatever amount that might be, Avas likewise entered in an 



Ad) 

 adjoining column. The corresponding values of AO and — were then easily com- 

 puted for each disturbance, whether it occurred in both components or in one only. 



Trustworthy contemporaneous readings of the two magnetometers commence with 

 February, 1841, and continue to the close of the series in June, 1845; there is, 

 however, an interval of time between the readings of the instruments which wc arc 

 obliged to disregard ; it amounts to but 5 minutes, the bifilar magnetometer having 

 been read so much later. 



As there is not generally a contemporaneous disturbance in the vertical and hori- 

 zontal force, the total number of disturbed values obtained by the process explained 

 above and employed, is necessarily much greater than it was for either of the com- 

 ponents; it becomes therefore necessary to fix upon some limit of recognition for a 

 disturbed value of the dip, and also of the total force. This is best done by the 

 adoption of that value which will separate an equal proportion of disturbed values 

 from the total number, as was done in the components ; for the vertical component 

 one in every 10.5 observations, for the horizontal component one in every 19.3 

 observations was separated as a disturbed value between February 1, 1841, and 

 June 30, 1845; on the average, therefore, one in every 15 observations should be 

 separated in the dip and total force series. During the time mentioned the number 

 of observations of vertical force was 22,092, and of horizontal force 22,150, from 

 which we should accordingly derive nearly 1470 disturbances. Now the number 



Ad) 

 of computed values of AO and of-— is 2362, hence, marking in each set the 1470 



highest values, the limit of + l.'l is reached in the dip, and +0.00094 in the total 

 force, which constitute the limiting values at and beyond which disturbances are 

 recognized in each element. To render the series of disturbance results homo- 

 geneous," the disturbances at the odd hours after October, 1843, have been omitted. 

 At Toronto the limit for the recognition of disturbances in the dip'^' was l.'O, and 

 in the total force 0.0004 parts of the force. 



ANALYSIS OF THE DISTURBANCES OF THE INCLINATION. 



The number of values of inclination differing +l.'l or more from their normal 

 amount, and which constitute the disturbance values is 1446, these are variously 

 combined in the following tables, and, when necessary, are separated into two 

 classes, those which increase and those which decrease the inclination; to the former 

 the sign -f- is prefixed, to the latter the sign — . The aggregate and mean amount 

 of disturbances are expressed in minutes of arc. The columns containing the num- 

 ber of disturbances are headed with the letter n. AVhen ratios arc given, they 



' Vol. Ill, p. xliii. 



