GENERAL SIR EDWARD SABINE ON TERRESTRIAL MAGNETISM. 
425 
The earliest conclusion of a systematic character regarding the phenomena of 
Terrestrial Magnetism, which is consistent with, and has been borne out by, our more 
recent as well as by our present knowledge, is that of Halley, contained in a paper pre- 
sented to the Royal Society in 1683 ; in which paper he demonstrated the impossibility 
of reconciling the magnetic Declinations which had been observed by “ persons of good 
skill and integrity” in different parts of the globe (of which Declinations he subjoined a 
Table), with the Theory, then recently proposed, of “Two Magnetical Poles, and an 
axis inclined to the Axis of the Earth.” Subsequent experience has abundantly con- 
firmed the soundness of Halley’s conclusion. The Records of Navigators and of 
Travellers, in the nearly two centuries which have since elapsed, have practically demon- 
strated its truth. Slowly as conviction may have made its way, there are probably few 
remaining (who have studied with due care the researches of the past and of the 
present centuries) who still hesitate to accept the conclusion to which Halley was led 
by the careful study of the Phenomena as they were then known — viz. that “ the Globe 
of the Earth may be regarded as one great magnet, having Four Magnetical Poles, or 
Points of Attraction, two of them near each Pole of the Equator ; and that in those 
parts of the world which lie near any of those magnetical Poles, the needle is chiefly 
governed thereby, the nearest pole being always predominant over the more remote.” 
Hansteen, in his memorable work, the ‘Magnetismus der Erde,’ published in 1819, 
brought together the observations of the Declination which had been previously scattered 
in voyages and travels and in the works of systematic writers (including those which had 
been collected by Halley), and formed from them maps of the phenomena corresponding 
to successive Epochs. Copies of the greater part of these maps were published in 
an abstract of the contents of the ‘ Magnetismus der Erde ’ which I drew up for the 
British Association for the Advancement of Science in 1835, and which was printed in 
the Report of the Dublin Meeting of the Association for that year. The first of 
these maps, corresponding to the observations of the Declination between 1600 and 
1700, is the earliest digest of contemporary determinations sufficiently extensive to 
warrant general conclusions. The present contribution may be regarded as a progres- 
sive step in the work thus commenced by Halley and continued by Hansteen — a con- 
tinuation in the same direction as that pursued by the two authorities whose footsteps 
I have endeavoured to follow, but with resources which attest the increased importance 
which has since attached to the subject. 
The amount of “ new material ” which has accumulated since the publication of the 
‘Magnetismus der Erde’ in 1819, abundantly testifies the increased interest with which 
this branch of Physical Geography has been since, and is now, regarded. The knowledge 
which we have since acquired of the magnetic phenomena in the northern portions of 
both the old and the new Continents may well be regarded as constituting an era in the 
history of its progressive advancement. What has been achieved for the northern parts 
of Europe and Asia by the researches of the eminent men who have made that field of 
research their own, has been paralleled in the New World by the prominence which 
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