156 Magnetism of the Earth. 
tively in meridians 120° on either side of the Hudson’s bay maximum, 
and 60° on either side of the Siberian maximum. In like manner, 
the variation in the 55th parallel is 0 in the longitude of the minimum 
of Dip, 42° east ; is easterly, increasing, for the next 30° of longi- 
tude, and easterly, decreasing, for the following 30°; so that the va- 
riation becomes again 0 in, or about the meridian of 102° east, which 
is that of the Siberian maximum. 
In the sincere hope that this letter may be instrumental in promo- 
ting this highly curious and philosophical enquiry, which would be the 
best return I can make to M. Hansteen for his kindness in giving me 
so early and so full an account of the progress of his discoveries, 
remain, my dear Sir, 
very faithfully yours, 
Epwarp Sasine. 
P. S. Since I wrote the above I have substituted a needle made 
by M. Dollond for myself, for one of the two which originally be- 
longed to M. Hansteen, and which it was my first intention to have 
sent you. You will perceive by the memoranda which accompany 
the needles, that No. XX. (the one I haye substituted,) has remain- 
ed perfectly steady in its magnetism, for a twelve month past, and 
will probably, therefore, continue so. No. XI. (which I received 
from M. Hansteen three years ago,) has increased its time of making 
300 vibrations, from 15’ 46.1” to 15’ 52.7”, since June 1827, when 
the last published observations were made with it; Phil. Trans. 1828, 
Art. I. page 14 ; consequently its magnetism has diminished in two 
years, between one and two parts in one hundred. It will be pru- 
dent, however, to treat both needles as if liable to farther changes. 
