Capt. Sabine’s observations on the magnetic needle. 141 
The mean Greenwich time is given, as it determines the 
amount of the sun’s polar distance. 
The latitudes and longitudes are of the spot, deduced by 
the ship’s log from the nearest observed. 
The altitudes are corrected for index error only, the letters 
or signs annexed denote the limb, and whether by reflection 
or by the natural horizon. 
The observed azimuths are of the sun’s centre cleared of 
index error ; the compasses used were No. 1 and 2, supplied 
to the Isabella, and No. 3 to the Alexander ; the true azimuths 
deduced from the elements contained in the preceding columns, 
are expressed in a corresponding manner to the reading of 
the compass, for the purpose of comparison. 
The observations were made on ice, except when otherwise 
noted in the column of remarks. 
When due consideration is given to the greatly diminished 
power, wdth which the earth’s magnetism acts on the hori- 
zontal direction of the needle, when the dip becomes so con- 
siderable as it was found in Davis’s Straits and Baffin’s Bay, 
namely, from 83° to 86°; the satisfactory results which have 
been obtained, even under such extreme circumstances with 
Captain Kater’s compasses, afford the best testimony of their 
excellence, and of the precision which may be expected from 
them in the ordinary course of observation. 
It may also be remarked, that a difference in the result of 
azimuths observed at different hours of the day may not be 
altogether an error of observation, since it is probable that as 
the directive power of magnetism diminished, the causes 
which produce the hourly change in the variation itself may 
act with increased effect. 
