408 
MR. CHRISTIE ON THE MAGNETICAL OBSERVATIONS 
the mean of the results at Point Ogle ; the values of I deduced from the last equa- 
tion ; and, for comparison with these, the relative intensities, assuming the intensity 
at London to be the theoretical value so determined. I have also given the values 
of ;jj resulting from the equation 
p — I. */(3 cos 2 & + 5) (21.), 
by assuming for I the ratio of the intensity to that at London, as deduced from the 
observations ; and taking the mean of these values, (excluding that for London, on 
account of its incongruity with all the others,) as the value of ^ in the equation (19.), 
I have deduced the values of I from that equation, and given the differences between 
these values and those resulting from the observations. 
Place of observation. 
Dip. 
Ratio of 
intensity 
to that at 
London. 
Computed 
value of I, 
equation 
(20.). 
Value of I 
deduced 
from 
observation. 
Difference. 
Value of 
constant ft, 
equation 
(21.). 
Difference 
between 
values of ft 
and mean. 
Computed 
value of I, 
eq uation 
(19.) 
ft = 1*7927. 
Error of 
computed 
value of I. 
London 
O 
69 
43 
1-0000 
1-7166 
1-7166 
+ •0000 
1-6496 
New York 
72 
49 
1-1327 
1-7804 
1-9445 
+ •1641 
1-7995 
+ •0068 
1-1285 
-•0042 
Fort Alexander . . 
78 
54 
1-2295 
1-8973 
2-1107 
+ •2134 
1-8330 
+ •0403 
1-2025 1 
-•0270 
Cumberland House 
79 
30 
1-2018 
1-9073 
2-0630 
+ •1557 
1-7822 
— •0105 
1-2088 
+ •0070 
Isle a la Crosse . . 
79 
28 
1-1893 
1-9068 
2-0416 
+ •1348 
1-7642 
-•0285 
1-2085 
+ •0192 
Fort Chipewyan. . 
81 
1 
1-2071 
1-9306 
2-0726 
+ •1420 
1-7684 
— •0243 
1-2237 
+ •0166 
Fort Resolution . . 
82 
3 
1-2320 
1-9450 
2-1150 
+ •1700 
1-7917 
— •0010 
1-2328 
+ •0008 
Fort Reliance. . . . 
84 
1 
1-2545 
1-9682 
2-1535 
+ •1853 
1-8028 
+ •0101 
1-2475 
-•0070 
Musk-Ox Rapid. . 
85 
54 
1-2572 
1-9851 
2-1581 
+ •1730 
1-7915 
— •0012 
1-2580 
+ •0008 
Rock Rapid .... 
87 
40 
1-2847 
1-9951 
2-2055 
+ •2104 
1-8214 
+ •0287 
1-2645 
-•0202 
Point Beaufort . . 
88 
3 
1-2422 
1-9965 
2-1324 
+ •1359 
1-7598 
-•0329 
1-2654 
+ •0232 
Montreal Island. . 
87 
36 
1-2606 
1-9948 
2-1639 
+ •1691 
1-7874 
— •0053 
1-2643 
+ ■0037 
Point Ogle 
89 
24 
1-2799 
1-9997 
2-1971 
+ •1974 
1-8103 
+•0176 
1-2674 
-•0125 
Mean . . 
1-7927 
1 
Admitting the accuracy of the results by which the intensities at the American 
stations are connected with the intensity at London, the results in this Table are, I 
consider, quite conclusive against the correctness of the formula on which the value 
of I depends, and, consequently, against that of the hypothesis from which it is 
deduced, if applied to the whole of this extent of the earth’s surface; the intensities 
deduced from observation at the American stations, as compared with the intensity 
at London, being, without any exception, considerably in excess of the theoretical 
results. But if we look to the values of p in the sixth column, excluding that for 
London, we cannot fail to be struck by their remarkable agreement with each other ; 
and I must candidly confess, that although, previously to deducing these results, I 
might expect something like a tendency to agreement, yet I by no means anticipated 
such an accordance as is here manifested. If we examine the differences between 
the values of p and its mean value, excluding that for London, we shall see that only 
in one instance does this difference amount to one forty-fifth of the mean, and rarely 
to one sixtieth. Although a comparison of the observed and computed intensities 
