ON THE PHENOMENA OF TERRESTRIAL MAGNETISM. 87 
dilation were perfect, would be the correct positions of the 
points of convergence due to the stronger axis. The position 
of that axis being in this manner approximative^ gained, its 
corrected situation was employed, in conjunction with the varia¬ 
tions observed near the poles of the weaker axis, in giving fresh 
points of convergence for that axis ; the new r position of which 
axis was in its turn again employed in recorrecting the variations 
observed near the stronger poles, and in producing a still nearer 
approximation to the position of the stronger axis. This alter¬ 
nating process was continued until the two last-found results ex¬ 
hibited no material difference. 
The approximate places of the extremities of the magnetic 
chords having been thus found and substituted for the points of 
convergence, and the values previously calculated of e, t), &c. 
deduced afresh, M. Hansteen reverted to the observations of 
dip in the high magnetic latitudes, from which he had previously 
derived values for the length and proportionate forces of the mag¬ 
netic axes, and selecting several of the most trustworthy of these 
observations, after various trials, he found that the observations 
were best represented when the length of each of the axes was 
taken at one third of the earth’s axis, and the ratio of the forces 
as 1*7724 to 1. 
With an axis of this length the points of 90° dip and of con¬ 
vergence of the horizontal needle would be nearer the end of 
the magnetic chord than in the case of an infinitely small axis ; 
and by trial it was found that u = 0*41 h r suited best. Other 
small corrections, which were pointed out by the comparison of 
the calculation and observations, were also introduced in several 
of the elements. 
Having reached this stage M. Hansteen considered that the 
elements were sufficiently corrected to admit of a more exten¬ 
sive comparison. He formed, therefore, a table of the most trust¬ 
worthy observations of dip, variation, and intensity, made between 
1787 and 1800, at eighty-four places, taken indiscriminately on 
the earth’s surface, and divided into three portions, magnetic 
north polar, south polar, and equatorial. With the observations in 
this table, the dip, variation, and intensity computed for each of 
the eighty-four stations were compared, by which still further 
but very small corrections were introduced in the elements. 
The principal elements for computing the magnetic phenomena 
thus corrected are as follow : 
Stronger Axis. Weaker Axis. 
a = 3° 13' . 5° 30' 
e = 29 0 28 28 
? = 291 51 95 58 E, of Greenwich, 
l - 129 49 .. 46 40 
