88 



" Declination at York Fort, 1857. 

 h m o t 



17th August, 5 30 P.M 7 01 E. 



5 43 P.M 7 21 E. 



6 14 P.M 7 43 E. 



20th August, 5 16 P.M 7 41 E. 



5 53 P.M 7 24 E. 



26th August, 5 54 A.M 8 01 E. 



640 A.M 7 57 E. 



7 20 A.M 750E. 



Mean 7 37 E. 



" Ten to twelve observations in each set, the compass being lifted 

 and shaken between each observation." t 



The observations of Franklin in September 1819 gave 6 00 E. 



Those of Lefroy in July 1843 gave 9 25 E. 



Those of Blakiston in August 1857 gave 7 37 E. 



It appears therefore that the secular variation which between 1819 

 and 1843 caused an increase of east decimation, caused on the con- 

 trary between 1843 and 1857 a decrease of east declination. This 

 is a reversal in the same sense as that which has been seen to have 

 taken place at Toronto. It seems probable from an inspection of the 

 intervals, and of the differences of declination-value, in the three 

 determinations above noticed, that the epoch of reversal must have 

 coincided very nearly with that of the survey of 1843-44 ; and con- 

 sequently that Lieut.-Col. Lefroy's result may show approximately 

 the maximum which the easterly declination attained at York Fort 

 before the change took place. If we might assume 1843 to be the 

 precise epoch, it is deserving of remark that it is the same year in 

 which the observations of the inclination at Toronto show that the 

 annual secular variation of that element changed from a decreasing 

 to an increasing rate. The dip observed by Lieut. Blakiston at 

 York Fort was 83 53' in 1857, and by Lieut.-Col. Lefroy 83 47 N 2 

 in 1843, showing, as at Toronto, a slight increase to have taken place 

 in that element in the interval. 



I am indebted to Dr. Norton Shaw, Secretary of the Royal Geo- 

 graphical Society, for a copy of declinations observed by Mr. Palliser 

 in his passage between Fort William and the Red River Settlement. 



