GG 
FIFTH REPORT- 1835, 
would have borne a detailed examination, in the same manner 
and to the same extent as is given of the line of no dip; but 
this would obviously have occupied too much space. M. Han- 
steen refers to the observations collected in the Appendix, as 
containing the authority for, and proof of, each line; adding 
his own assurance that an equally scrupulous care has been be¬ 
stowed on all. Each line, separately considered, affords a 
distinct evidence of systematic inconsistency with the hypothesis 
of a single magnetic axis. The line of no dip has been selected 
as an example, because it is the line most usually referred to in 
such discussions. 
A summary of the principal changes that have taken place in 
the dip in various parts of the world, from the earliest observa¬ 
tions to the present time, is as follows : the north dip has in¬ 
creased in North America, diminished in Europe, and increased 
in eastern Asia and Japan ; the south dip has decreased in South 
America, has been nearly stationary near the Cape of Good Hope, 
and has decreased in the vicinity of the Straits of Sunda and 
a t 
New Holland. 
The remainder of this chapter is occupied in considering the 
few observations of the magnetic force that had been made when 
M. Hansteen’s work was published. In the hypothesis of a sin¬ 
gle magnetic axis, it is a well-known law that the force should 
increase from the magnetic equator towards each of the mag¬ 
netic poles, according to a certain function of the dip ; conse¬ 
quently that all places having the same dip should have the 
same intensity. It is shown, however, that the observations not 
only do not accord with this law, but that they present marked 
and systematic differences from it. Comparative observations 
of the magnetic force in places in Europe and in America, hav¬ 
ing the same dip, show uniformly that a less intensity prevails 
in Europe than in America. In tracing along any of the lines 
of dip on which such comparative observations have been made, 
the intensity is found progressively to diminish from a maximum 
on the western side of America, to a minimum in the western 
parts of Europe, in those lines of dip which are included in the 
latitudes of Europe, and in somewhat more easterly meridians in 
those which approach the geographical equator, as well as in those 
further to the south. In tracing any of these lines still further 
to the eastward, the intensity again increases. 
A second systematic difference from the law founded on a sin¬ 
gle magnetic axis is the following. In places lying under the 
same geographical meridian, a much greater increase of force 
corresponds to a given increase of dip in the meridians of New 
Holland and America than in those of Europe and Africa. 
