OBSERVATIONS OF THE MAGNETIC FORCE. 
301 
“ Remarks referring to Table XXXIX. 
“ Sault St. Mary, November 4, 1844. — The observations of vibration of No. 31 were accidentally omitted at 
this station, by the interruption occasioned by the sudden death of one of the voyageurs ; the value of X given 
171 
in the table was deduced from the experiments of deflection, by applying to the observed value of the ratio — 
A 
the known values of m, as given by the observations of September 6, 19, 25 and 29, and October 11, 1844, 
viz. 0*3 ; in the general mean it is allowed only half the weight of the complete observations. 
“Fort William, May 31, 1843, and October 11, 1844. — The reduction of the observed values of X to the 
mean of the bifilar readings is omitted in the observations of October 11, 1844 : the magnetometer was observed, 
but the connection of the readings did not appear satisfactory. 
“ Fort Francis, June 14, 1 843, and September 29, 1844. — The bifilar was not adjusted for the observations of 
1844; the value of X by No. 30 in 1844 differs considerably from the mean values by the two other bars, but 
not to a greater extent than might have been caused by actual changes of the force. 
“ Rat Portage, September 25, 1844. — The unfavourable state of the weather obliged the observations to be 
made in a dwelling-house, which like all the dwelling-houses in that part of the north of America was con- 
structed of wood, with scarcely any iron whatever ; the floor was laid with trenails, and the lock on the door 
was a wooden one ; hence it is considered that the observation is as unexceptionable as if made in the open 
air : the bifilar was not in adjustment. 
“ Winnipeg River, June 21, 1843. — The value of X is deduced from observations of deflection only, employing 
the mean values of m given by the complete observations of June 14 and June 30. 
“ Upper Fort Garry, June 30, 1843. — The time of vibration of No. 30 was observed with the weights 5 and 6 
attached*, but the second set without the weights could not be taken. The observed value of T' 2 has been 
multiplied by 0*338, the value of the ratio - — — to obtain the value of T-, and the square root of the product 
K + K r 
(4*9748) inserted in table No. XXXVIII. ; a few vibrations (22) which were observed as a check, gave a mean 
value of 4*912. 
“Norway House, July 14, 1843, and September 6, 1844. — The value of m of bar 31 in 1843, appears too 
small, being 0 - 012 less than the mean at the preceding and following stations; the value of X is slightly in 
excess of the mean of the other two bars (2*178 instead of 2*174), indicating the error to be probably in the 
experiment of deflection. The observations of 1843 are reduced to the mean of corresponding readings of the 
bifilar ; those of 1844 are reduced to the mean of hourly readings continued for twenty-one hours. 
“ York Factory. — The day of observation at this station, the 26th of July 1843, was one of very consider- 
able magnetic disturbance, and in other respects unfavourable, being windy and showery; the tent which shel- 
tered the bifilar magnetometer was blown down, and the glass tube of the instrument broken, rendering it for 
the time unserviceable. In consequence of this accident the time of vibration of No. 31 is not reduced to the 
same value of the horizontal force as the other parts of the experiments ; and the mean values of X, by bars 30 
and 31, differ to an amount which is very large, when compared with the small value of the horizontal com- 
ponent at the station, i. e. -^th its whole amount. 
“ Cross Lake, August 16, 1843. — This was the first occasion on which the bars were vibrated without the 
stirrup. The bifilar was not in adjustment. 
“Cumberland House. — The bars were vibrated in 1843, both with and without the stirrup, and the mean 
horizontal intensity is deduced from all the resulting values of X. The bars were vibrated again in August 
1844 with the same mode of suspension, but the experiments of deflection were not made. 
“ Carlton House, August 26, 1844. — The bifilar was not adjusted at this station; and as the experiments of 
deflection with No. 17 were omitted, the mean value of X is deduced from the observations with bars 30 and 
31 only. 
* This was done at several of the stations ; but the values of K so obtained have been superseded by the 
more accurate determination with the brass rings. 
MDCCCXLVI. 2 R 
