394 
MR. CHRISTIE ON THE MAGNETICAL OBSERVATIONS 
To this Table of the direct results of the observations, it is necessary that I should 
add a few remarks of Captain Back’s, on circumstances connected with the observa- 
tions, and of my own, on the observations themselves. 
At Montreal, Captain Back remarks, that “ from some mistake of the assistant the 
observations were so confusedly set down as to be useless and afterwards, that 
“ not having- an assistant to take time, See. I adopted this plan that is, the time at 
which the needle commenced vibrating- being- noted, the vibrations were counted until 
the semi-arc of vibration was reduced to 2° or 3°, and the time again noted ; so that, 
in each case, the time could not well be determined more accurately than to the 
nearest second. He subsequently instructed his servant William Mally in the 
manner of noting the time by chronometer ; and although, as I am sorry to have to 
notice, there are, in the early observations, manifest errors in the time, yet this person 
appears, from the greater detail in the observations at Fort Reliance and subsequently 
(the arc and time being- each noted at every tenth vibration), to have given very 
efficient assistance in this operation. In the foregoing Table I have marked with an 
asterisk those observations in which I consider that an error must have been made, 
either in the time or the number of vibrations, and which I have consequently omitted 
in taking the mean ; and it will be proper that I should point out more particularly 
the results which these observations give. 
At Cumberland House, with the face of the instrument east and the needle reversed 
on its axis, 112 vibrations appear to have been made in 3 in 9 s , giving l s, 6875 as the 
time of one vibration, wdiich is so greatly at variance with the other results, that no 
conclusions could possibly be drawn from a mean in which it should enter. We may 
conceive that an error of ten vibrations in counting, or of one minute in the time, 
may easily have been made, but neither supposition would give a result at all in ac- 
cordance with the others. It is scarcely conceivable that any change in the terrestrial 
intensity, whether arising from atmospheric or any other influence, could have caused 
so great an increase in the time of vibration ; it is, however, proper to give Captain 
Back’s remarks on the weather, which I shall do after noticing other observations 
which have been omitted in taking the means. 
At Isle a la Crosse, with the face of the instrument west and the face of the needle 
to the face of the instrument, it appears that 72 vibrations were made in 2 m 30 s , the 
times at beginning and ending being 8 h 56 m 30 s and 8 h 59 m 00 s , by chronometer 
13 m 20 s slow of Greenwich time. This interval would give 2 S, 083 for the time oi 
vibration. If we suppose an error of one minute to have been made in the time, 
then I s 25 would be the time of vibration, a result by no means improbable; but I 
consider that the safest course is to reject the observation. With the face of the 
needle reversed and the face of the instrument east, the times at beginning and 
ending were 9' 1 50 m 30 s and 9 h 58 m 25 s . We may conceive that here in transcribing 
56 m may easily have been mistaken for 5Q m ; and this would reduce the interval in 
which seventy-four vibrations were made to l m 55 s , and the time of one vibration 
