MADE BY CAPTAIN BACK DURING HIS LATE ARCTIC EXPEDITION. 391 
column point to the same conclusions. It must however be borne in mind that the 
variations at Fort Alexander, Cumberland House, Isle a la Crosse, and Fort Chipe- 
wyan, which determine the positions of the pole of convergence in these cases, are 
those observed by Sir John Franklin in 1825, and that the dips at these places, which 
determine the situation of the pole of verticity, are those resulting from the observa- 
tions of Captain Back in 1 834 : so that these observations cannot be considered as 
strictly comparative. This objection cannot, however, be urged against the observa- 
tions from Fort Resolution to the sea, which give results equally discordant with the 
theory. 
We have already seen that the dip at the several stations, as determined from the 
constant value of the angle y, differs, and in some cases considerably, from that 
deduced from the value of that angle determined by means of the relative intensities. 
It may therefore be satisfactory to inquire whether, by employing the dips obtained 
from these values of the angle 7 , we shall obtain results more accordant with theory. 
In the following Table I have arranged the results in the same form as in the preceding, 
the variations and magnetic polar distances employed being those there given. 
Places from the observations 
Observed 
Magnetic 
Error, or 
Value of 
Value of 
Error, or value of 
at which the position of the pole 
variation 
polar 
Dip. 
tan 5 . tan 
value of 
d . d 
3 cos 2 J +5 
d.S 3 cos 2 5 +5 
of convergence is determined. 
of the 
distance. 
tan £ .tan <P— 2. 
d.x' 
4 
d.X 4 
needle. 
o / n 
o / // 
Fort Alexander 1 
15 16 E. 
28 22 43 
78 6 3 
2-5815 
+ 0-5815 
•7944 
•5552 
+ -2392 
and Cumberland House J 
19 14 E. 
26 16 11 
79 46 34 
2-7366 
+ 0-7366 
Cumberland House 
19 14 E. 
22 20 28 
79 46 34 
2-2786 
+ 0-2786 
-1-3975 
•5485 
- 1-9460 
and Isle a la Crosse 
23 19 E. 
22 8 26 
79 29 45 
2-1944 
+ 0-1944 
Isle a la Crosse 
23 19 E. 
32 13 34 
79 29 45 
3-4005 
+ 1-4005 
•6375 
•5309 
+ -1066 
and Fort Chipewyan 
25 30 E. 
30 0 16 
80 54 44 
3-6101 
+ 1-6101 
Fort Chipewyan 
t ... 
25 30 E. 
21 19 2 
80 54 44 
2-4396 
+ 0-4396 
•8683 
•5317 
+ -3366 
and Fort Resolution 
... 
29 15 E. 
19 38 56 
82 21 39 
2-6621 
+ 0-6621 
Fort Chipewyan 1 
, ... 
25 30 E. 
10 6 50 
80 54 44 
1-1152 
- 0-8848 
•9795 
•5317 
+ -4478 
and Fort Resolution 
.. 
37 20 E. 
8 38 6 
82 21 39 
1-1322 
- 0-8678 
Fort Resolution 
I ... 
37 20 E. 
9 4 53 
82 21 39 
1-1917 
- 0-8083 
•7863 
•5198 
+ -2665 
and Fort Reliance 
'... 
35 19 E. 
6 28 11 
84 24 52 
1-1596 
- 0-8404 
Fort Reliance 
... 
35 19 E. 
7 13 11 
84 24 52 
1-2953 
- 0-7047 
■7823 
•5110 
+ -2713 
and Musk-Ox Rapid 
r... 
44 24 E. 
5 30 14 
85 45 24 
1-2987 
- 0-7013 
Musk-Ox Rapid 
44 24 E. 
7 52 46 
85 45 24 
1-8653 
- 0-1347 
■5616 
•5047 
+ -0569 
and Rock Rapid 
■... 
29 16 E. 
4 29 4 
87 39 48 
1-9220 
- 0-0780 
Rock Rapid 
[••• 
29 16 E. 
2 21 16 
87 39 48 
1-0076 
- 0-9924 
•1567 
•5022 
- -3455 
and Point Beaufort 
6 00 W. 
0 14 28 
87 59 40 
0-1201 
- 1-8799 
Rock Rapid 
and Montreal Island 
k:: 
29 16 E. 
2 00 W. 
2 29 56 
0 19 30 
87 39 48 
87 27 13 
1-0695 
0-1275 
- 0-9305 
- 1-8725 
- -0965 
•5027 
- -5992 
Fort Alexander 1 ... 
15 16 E. 
27 55 38 
78 6 3 
2-5156 
+ 0-4844 
•6872 
■5432 
+ -1440 
and Fort Resolution [... 
29 15 E. 
21 43 42 
82 21 39 
2-9713 
+ 0-9712 
Fort Alexander 
15 16 E. 
23 9 47 
78 6 3 
2-0304 
+ 0-0304 
•7968 
•5432 
+ -2536 
and Fort Resolution 
r... 
37 20 E. 
17 49 1 
82 21 39 
2-3962 
+ 0-3962 
Fort Reliance 
L- 
35 19 E. 
10 53 26 
84 24 52 
1-9673 
- 0-0327 
•6258 
•5072 
+ -1186 
and Rock Rapid 
f- 
29 16 E. 
5 41 56 
87 39 48 
2-4456 
+ 0-4456 
Although the differences here shown between the results of theory and those de- 
duced from the observations are in some cases less than in the preceding Table, yet 
in others they are greater ; and the comparison does not upon the whole show a 
nearer coincidence. If this want of coincidence is to be attributed to errors in the 
observations, I think that the two comparisons which I have instituted indicate errors 
in the observed variations rather than in the dips of the needle, which have been de- 
duced from the observations. The character of the differences between the theory 
