66 SEVENTH REPORT—1837. 
accordance with facts, simplicity recommends itself to all; 
and persons imperfectly acquainted with the phenomena may 
have been led by it to undervalue observation, when detached 
portions of its facts, inconsistent with the hypothesis, may have 
come under their notice; and, departing from the principles of 
inductive philosophy, may have suffered themselves to look to 
the hypothesis rather than to the phenomena. The simplicity 
of its resulting phenomena is, however, that characteristic in 
which it specially departs from the facts of nature. The real 
phznomena are complex, as all who have studied them will 
most readily admit; and it can scarcely be expected that the 
laws which are to represent them should not also have in some 
degree an appearance of complexity, until the laws of their 
causation shall be discovered. 
In a science which stands in need of national aid for its ex- 
perimental extension, it is peculiarly desirable to remove such 
erroneous impressions as militate against a belief in the value, 
and consequently the importance, of experimental research. 
I propose, therefore, in the first place, to show, that the irre- 
concilability of a single central axis does not rest on insulated 
facts only, or, as some may have supposed, on the conclusions 
of a single observer, but that all those who have principally 
concurred in extending the boundaries of our experimental 
knowledge of late years, have arrived at the same conclusion 
in that respect, and have uniformly borne testimony to the in- 
applicability of the formule of that hypothesis to represent their 
respective observations; and, secondly, to direct the reader’s 
attention to those facts in particular, which may produce the 
readiest conviction of the systematic departure of the lines of 
dip and intensity from that law of the hypothesis by which they 
should have parallel courses. 
We have already seen the conclusion at which MM. Gay 
Lussac and Humboldt arrived in 1807, namely, that their ob- 
servations in France, Italy, and Germany, taken in conjunction 
with M. de Humboldt’s in America, could only be reconciled 
with M. Biot’s hypothesis, by supposing the existence of a 
secondary centre extending its influence over the continent 
of Europe, and acting conjointly with the primary. 
From 1807 the spirit of experimental inquiry slumbered for 
a while; the times were unpropitious to a research which re- 
quired freedom of access to different countries, and safety and 
facility in traversing extensive spaces of the earth’s surface. 
At length it revived nearly simultaneously, in Capt. de Freyci- 
net’s voyage of circumnavigation, and in the British expeditions 
for the discovery of a north-west passage. Between 1818 and 
