of the Magnetic Poles of the Earth. 169 
and thence increases westward; that Capt. Parry found it on 
the 22d of August 1819, in latitude 74° 40' and longitude 
91° 47' = 128° 58’ W.; and on the 28th of August in latitude 
75° 9' and longitude 103° 45’, = 165° 50! Ey During the 
six days’ interval (those in which no observations were made), 
the western declination must have risen to 180° before it be- 
came easterly, as it was found on the 28th of August. Dr. 
Brewster thence concludes, that between the 23d and 28th of 
August the expedition must have been several degrees north 
of the great magnetic pole; adding, that this circumstance fully 
agrees with the position given to it for that year in my in- 
vestigation of the magnetism of the earth. 
Ifin these investigations we also consider the dip of the needle, 
it is evident that above the pole the dipping needle must assume 
a vertical position,—that here therefore the dip is 90°; that the 
same must decrease the further we remove from this point, 
that it disappears entirely somewhere near the equator, and 
at last becomes southerly. Thus, for instance, the northern 
dip in Paris is = 68° 38’, in Copenhagen = 70° 37’, in Go- 
thenburg = 72° 1', in Christiania = 72° 45, in Bergen = 
74° 3! &c. ‘Therefore the observations on the dip may also 
be referred to, if we wish to ascertain the position of the mag- 
netic pole of the earth.—The observations made on this sub- 
ject by the two English north polar expeditions are contained 
in the two following tables : 
I. Observations made during the voyage of Captain Ross. 
a 
1818. 
pa Long. W. from A 
North Lat. rah bear Dip. 
/ 
51 
April 
June 
July 
August 
Sept. 
Nov. 3 
1819. March 
* Regent’s Park, London, + Island of Brassa, Shetland. 
‘{ Hare Island, § Onthe three Baffin’s Islands. 
|| Island of Brassa. 1 Regent’s Park, London. 
Vol, 67. No. 335. March 1826. x II. Ob- 
