OBSERVATIONS OF THE MAGNETIC FORCE. 
303 
Determination of the absolute Horizontal Force derived from the times of vibration of 
the magnets of the portable unifilar magnetometer in 1844. 
It has been seen by the preceding Table. No. XXXVIII., that there were sixteen 
stations at which observations of deflection as well as vibration were made with the 
magnets of the portable unifilar in 1844, and that at three of the stations they were 
made at two different epochs : there were also twenty-five other stations, visited in the 
same year, at which the times of vibration only of the magnets are derived ; and in 
respect to these we have in the first instance to derive the magnetic moment of each 
magnet, at the several periods when the vibrations only were observed, from the 
deflections at the stations where both processes were completed ; and having thus 
obtained a knowledge of the variations which the magnetism of the bars may have 
undergone from time to time in the course of the year, we shall be enabled to derive 
the values of the absolute horizontal force at those stations also, or at least at a great 
part of them, where the vibrations alone are observed. 
The observations, which include the deflections as well as vibrations, have been 
discussed by Captain Lefroy in the preceding pages; and we are thus furnished with 
nineteen determinations of the magnetic moment of No. 30, seventeen of No. 31, and 
fourteen of No. 17, at different times in the course of the year. 
The values of m (the magnetic moment) of No. 30 at the stations at which the 
deflections are observed, were as follows, viz. — 
Athabasca, March 2, 1844 . , m= , 4207. 
Fort Simpson, May 2, 1844 . m='4166. 
FortGood Hope, May 29,1844 m—' 4106. 
Fort Norman, June 2, 1844 . m= - 4091. 
Fort Simpson, June 12, 1844 m= - 4018. 
FortResolution, June24, 1844 tw = - 4002. 
Athabasca, July 2, 1844 . . m = ’3988. 
FortVermilion, July 1 1, 1844 tw = '4005. 
Fort Dun vegan, July 24,1844 m= , 3992. 
Fort Edmonton, Aug. 1 8,1844 ra = , 3978. 
Carlton House, Aug. 26, 1844 m—‘ 3965. 
Norway House, Sept. 4, 1844 m—' 3967. 
Fort Alexander, Sept. 20,1844 m=’ 3962. 
Rat Portage, Sept. 25, 1844. m—’ 3964. 
Fort Francis, Sept. 29, 1844 . m=‘3962. 
Fort William, Oct. 10, 1844. ?n= - 3962. 
SaultSt. Mary, Nov. 5, 1844. m=*3940. 
Toronto (with the stirrup), 
January 1845 m—' 3947- 
Toronto (without the stir- 
rup), Jan. 29, 1 845 . . . m=‘ 3931. 
An inspection of these values shows that the magnetism of No. 30 was not constant 
during the period under consideration, but that a progressive loss took place, which 
was considerable in amount between March and June, but became much smaller 
and more regular between June 1844 and January 1845. 
The whole of the twenty-five stations at which the times of vibration only were 
observed, are comprised between Fort Dunvegan on the 24th of July, 1844, and To- 
ronto on January 29, 1845, or during the period when the loss of magnetism of 
No. 30 was small and tolerably regular ; we may therefore assume for this portion of 
2 r 2 
