DETERMINATIONS OF LATITUDE AND LONGITUDE. 
261 
the map. Four of the eleven omitted stations are in a district, rich in minerals, on 
the south side of Lake Superior, near the 272nd geographical meridian: in each of these 
four instances the effect of the disturbance has been to increase the Inclination, 
but there are other stations in the same district where the observed Inclination does 
not materially differ from that which is due to the geographical position ; and there 
is one station (United States Agency) where it is some minutes in defect. In the 
cases referred to, the influence of the disturbing causes is rather to produce irregu- 
larity at individual stations, than a systematic derangement of the general direction of 
the magnetic lines, similar to the highly interesting phenomenon in the northern part 
of Bohemia, recently investigated by M. Kreil* ; from which investigation we learn 
that a more systematic relation may exist in some localities between geological and 
magnetical phenomena than had been previously apprehended. But instances of 
disturbance even at individual stations in the countries included in this survey are so 
unusually rare, that we should the less expect to find districts exhibiting a systematic 
affection : of such I can perceive no traces ; the direction of the lines conforms to 
the general magnetic system of the globe, and appears to suffer no material inter- 
ruption ; such district anomalies either do not exist, or the observations have not 
brought them to light. 
Determinations of Latitude and Longitude. 
The geographical positions of the stations visited by Lieut. Lefroy in 1843 and 
1844 are given in Table IX., with the authorities on which they depend : the latitudes 
and longitudes entered in the column headed ‘ observed’ were either determined by 
his own observations, or reduced by himself by courses and distances from neigh- 
bouring stations of observation : to distinguish those stations at which the latitude 
or longitude was observed on the spot, a mark is inserted in the adjoining column : 
the mark O indicates latitude observed by meridian altitude of the sun ; the mark * 
by altitudes of Polaris : in the column of longitudes, the mark © indicates chrono- 
metrical longitudes deduced from observations of the sun’s altitude ; and the mark * 
from altitudes of a star : where no mark is inserted, the latitude or longitude was 
deduced by observation of courses and distances from the adjacent stations. The 
cbronometrical longitudes are dependent upon the longitudes of the following prin- 
cipal stations, as given by Sir John Franklin, Captain Bayfield, and others : viz. 
Fort William . 
Sault St. Mary 
("89 27 Bayfield. 
I 89 16 Franklin. 
| 89 23 Tiarks. 
L89 22 Mean 
. . . 84 34 Bayfield. 
* Magnetische und Geographische Ortsbestimmungen in Bohmen ; Prag. 1846. 
MDCCCXLVI. 2 M 
