412 
MR. CHRISTIE ON THE MAGNETICAL OBSERVATIONS 
Place of observation. 
Fort Reliance. . 
Musk-Ox Rapid 
Rock Rapid . . 
Point Beaufort 
Montreal Island 
Point Ogle 
Observed 
Dip. 
84 1 
85 54 
87 40 
88 3 
87 36 
89 24 
Needle No. 1. 
Needle No. 3. 
Lozenge-needle. 
Computed dip 
cos 3 = . — - — 
I M 
I = -138417. 
Difference of 
computed and 
observed dip. 
Computed dip 
cos 2 = — - — 
IM 
I = -144429. 
Difference of 
computed and 
observed dip. 
Computed dip 
cos 2 = \ 
I M 
I = -818545. 
Difference of 
computed and 
observed dip. 
O / II 
84 27 54 
+ 26 54 
O 1 II 
84 30 29 
85 58 40 
O 1 II 
+ 0 29 29 
+ 0 4 40 
+ 0 29 21 
+ 1 0 32 
+ 1 16 35 
-0 0 6 
Oil/ 
84 24 35 
+ 0 23 35 
88 9 21 
89 3 32 
88 52 35 
88 49 31 
89 17 49 
+ 1 13 31 
-0 6 11 
89 23 54 
Fort Reliance . . 
Musk-Ox Rapid 
Rock Rapid . . 
Point Beaufort 
Montreal Island 
Point Ogle .... 
I = -131253. 
84 9 43 
+ 8 43 
I = -137573. 
84 14 1 
85 46 38 
3 51 
0 43 
88 49 14 
89 22 6 
88 
89 
+ 0 13 1 
-0 7 22 
+ 0 23 51 
+ 0 57 43 
+ 1 13 14 
-0 1 54 
I = -799485. 
84 16 34 
88 47 50 
89 16 48 
+ 0 15 34 
+ 1 11 50 
-0 7 12 
The differences between the observed and computed dips at Fort Reliance, Musk- 
Ox Rapid and Point Ogle, particularly in the latter part of this Table, are quite within 
the limits of errors in the determination of the dip. The difference at Rock Rapid 
may possibly be considered to exceed this ; but it is to be observed that the value of 
M in the Table, p. 408 , is at this place manifestly in excess, and I have before re- 
marked that the vibration of the needle No. II. appears to have been there influenced 
by some particular cause which would render the value of M, deduced from its time 
of vibration, doubtful. With regard to the differences at Point Beaufort and Mont- 
real Island, these are much greater than we can attribute to the errors to which the 
observations for the dip could be liable, considering the care which Captain Back ap- 
pears in all cases to have bestowed on these observations. All circumstances, how- 
ever, indicate that the dips deduced from the observations at these two stations are less 
than the truth ; and as there is one error which it is possible may have been made 
in registering the observations, it is proper that I should here advert to it. The value 
of the angle '6 at Point Beaufort is 89 ° 35 ' (Table, p. 380 ) ; and if we suppose that 
this arc was read on the southern limb of the instrument, as was the case at Point 
Ogle, instead of the northern, as it had been previously at Rock Rapid, and as it is 
registered, then the true value of '$ would be 90 ° 25 '. This value would give the dip 
at Point Beaufort 88 ° 28 ' instead of 88 ° 3 '. If we suppose the same error to have 
been committed at Montreal Island, then the value of '6 there would be 91 ° 13 ' 30 ", 
and the dip 88 ° 48 ' 30 " instead of 87 ° 35 ' 49 ". These results, particularly that for 
Montreal Island, from a comparison with those at Rock Rapid and Point Ogle, and 
also with those in the foregoing Table, are certainly very probable, and the error I 
have indicated is one which may easily have occurred ; but I must not omit to state, 
