SUPPLEMENT. 
33 
S. 40° E.; and a direction at right angles to that, S. 75° W., I 
assumed as the magnetic meridian in the first two sets of dip. 
The mean of these was 89° 58' 15 ". The next two sets were 
taken at an angle of 45°to the right of the former, and their 
mean result was 89° 59' 46" ; and the two last sets, exactly at 
right angles to the first set, gave the dip 89° 59 . In these last 
observations, the axis of the intensity needle was put, in the 
stead of its own axis, which accounts for the difference in the 
readings of the needle in its several positions, as will be seen 
by the table of dips* The reason for my doing this was to pro¬ 
vide against the possibility of the observations being influenced 
by an injury which the axis of the needle was supposed to have 
sustained, by the great difference that sometimes occurred in its 
indications. The result of these observations, however, shows 
that the injury, if it had met with any, did not materially affect 
the results; so perfectly do the principles of its construction 
counteract any slight bend in the axis, or any inequality in the 
balance of the needle. 
To complete the observations on the intensity of the magnetic 
force, and the various experiments which were made, and which 
it is unnecessary here to notice, occupied the whole of the time 
that I could devote to that purpose. And although there is a 
difference, amounting to several minutes, in the different obser¬ 
vations made in the same direction of the needle, yet the result¬ 
ant mean dip in each of the three directions in which they were 
obtained, placed us as near to the magnetic pole as, with our 
limited means, we were able to determine. And although it 
cannot but be a rough approximation, yet it is hardly possible 
to be more than a few miles from the exact position. It was, at 
any rate, quite impossible for us to know, now that the hori¬ 
zontal needle had ceased to act, in what direction to proceed for 
the purpose of approaching it more nearly; for in order to de¬ 
termine its exact position, the co-operation of several observers, 
placed at some distance, in various directions of its position, 
would be necessary. A series of observations, continued for 
some months, would afford the most important and interesting 
data. By such means, not only its actual position, but its diur- 
32 0 
