CIX 
OBSERVATIONS ON THE VARIATION, 
MADE ON SHORE, OR ON THE ICE, AT A SUFFICIENT DISTANCE FROM THE SHIPS TO 
BE BEYOND THE INFLUENCE OF THE IRON WHICH THEY CONTAINED. 
The Azimuth Compasses used in these Observations were of Captain 
Rater’s improved construction, whereof four were supplied to the Hecla, 
being numbered from 1 to 4, and are referred to accordingly. 
These Compasses were originally constructed for the Voyage of Discovery 
in 1818, and are described in the Philosophical Transactions for 1819 ; a further 
improvement having been made in them during the equipment of this Expedi- 
tion, the following particulars are added to the former Description : — 
A Needle, in figure and size as represented below, has been substituted 
for the straight Needle ; the Card is as before, with the addition of four talc 
Vanes fixed beneath and perpendicular to it, and at right angles to each 
other ; these are designed to check the Vibrations, and to cause the Needle 
to settle more speedily, by reason of the resistance which they experience 
from the air in the Compass-Box ; the Needle, Card, and Vanes, with the 
Agate Cup and Screws, weigh altogether 173| grains. 
The Compass was placed, during Observations, on a Brass Plate, furnished 
with Foot Screws by which it was adjusted horizontally, as shewn by a 
spirit level ; thus the perpendicularity of the Sight Vane was ensured ; a cir- 
cumstance to which it is necessary to be particularly attentive with these 
O 2 
