260 
MAGNETIC SURVEY IN NORTH AMERICA. 
suiting from the mean of the observed Inclinations : the comparison shows as 
follows : — 
Table VIII. 
Group. 
Long. 
Lat. 
No. of 
observations. 
Mean of the 
observed 
Inclinations. 
Computed 
tabular 
Inclinations. 
Tabular in 
excess or 
defect. 
l lm 
269 26 
42 28 
14. 
73 00-1 
72 59 
/ 
— 1 
2. 
269 59 
38 49 
8. 
69 38-7 
69 41 
+ 2 
3. 
275 36 
38 30 
6. 
70 06-1 
70 05 
— 1 
4. 
275 19 
46 21 
10. 
77 05-2 
77 06 
+ 1 
5. 
278 30 
41 18 
15. 
72 59-0 
72 59 
0 
6. 
285 58 
40 59 
11. 
73 01-3 
73 02 
+ 1 
7- 
288 49 
42 13 
11. 
74 ll-l 
74 09 
-2 
8. 
291 20 
46 06 
12. 
77 01*4 
77 00 
-1 
The tabular inclination corresponding to the geographical position of Toronto is 
75° 13''5. Dr. Locke’s observation in 1843 was 76° 13'*4. The needles of the ob- 
servatory gave a mean inclination for that year amounting to 76° 16\ The mean 
of the last year (1845) is 75° 15''5. So far as the absence of station error is an object 
in the choice of a situation for a magnetic Observatory, the site of the Toronto Ob- 
servatory appears to have been happily chosen. 
Taking single stations, there are seven at which the tabular dip differs more than 
1° from the observed ; at five of these the observed is in excess of the tabular, and 
at two in defect. The five are, — Kingston in Canada ; Otter Island on Lake Supe- 
rior ; two stations 500 feet distant from each other in the Magnetic Inlet, and one 
on the adjacent isthmus on the south side of Lake Superior. The two in defect are 
Chat Falls on the Ottawa River ; and the Portage Ecarte, near Lake Superior, to- 
wards the height of land which separates the waters which flow into Lake Superior 
from those which flow towards Lake Winnipeg. At all these stations the observa- 
tions of the magnetic Force, as well as those of the Inclination, manifest the existence 
of local disturbing influence. At Chat Falls the Inclination is in defect and the 
Force in excess ; at Otter Island the contrary is the case, the Inclination being in 
excess and the Force in defect. At Portage Ecart6, both Inclination and Force are in 
defect ; and at the three other stations both elements are in excess. Besides the 
seven stations where the station error appears to exceed 1°, there are four (Isle 
d’Urval and Kingsey in Canada; Pierre au Calumet on the Elk River; and the 
Eagle River, in the same mineral district on the south side of Lake Superior as the 
magnetic inlet) at which the observations appear to be affected by station error to an 
amount which is less than 1°, but is still considerable. At each of these four stations 
the observed dip is in excess. The Inclinations at the eleven stations which have 
been thus named, are omitted in the map accompanying this memoir: they are 
eleven out of 335 stations. Of the remaining 324 stations there are some at which 
local disturbance of a less amount may be inferred ; but all these are inserted in 
