PROGRESS IN SCIENCE IN TERRESTRIAL MAGNETISM. 335 
in Siberia. Sabine, whose experience in analyzing the regis¬ 
trations of the momentary and ephemeral changes of the 
Earth’s magnetic state was very great, thought that, “ of 
the two magnetic systems which are distinctly recognizable 
in the magnetism of the globe, one has a terrestrial and the 
other a cosmical source,” and that it is “ the latter of these 
two systems which, by its progressive translation, gives rise 
to the phenomena of secular change and to those magnetic 
cycles which owe their origin to the operation of the secular 
change,” concurring with the conclusion of Walker that, 
“ the magnetic influence at any point of the globe is the 
result of two distinct magnetic systems, the principal of 
which is the magnetic system proper of the globe, having 
its northern point of greatest attraction in the North Ameri¬ 
can continent, whilst the weaker system is that which 
results from the magnetism induced in the Earth by cosmical 
action, and of which the northern point of greatest attrac¬ 
tion is at present in the north of the Asiatic continent. Thus 
the direction of the magnet at any point results from the 
superposition of these two systems, the nearer pole being 
always predominant over the more remote.” The sagacity 
of this induction is borne out by the results obtained in 
later times by mathematical physicists. 
Among many remarkable facts about the Earth’s magnetic 
state one of the most remarkable is that there is a magnetical 
difference or want of symmetry between the two hemispheres, 
the northern and the southern. Now, the one great natural 
phenomenon with which this agrees is that of the Earth’s 
rotation, and there are many lines of thought which lead to 
the notion that the Earth’s magnetic state may have been 
originally produced by, even if it is not maintained by, the 
Earth’s diurnal rotation. 
The study of the diurnal changes presents a simpler 
problem than the general distribution and the secular 
changes of the Earth’s magnetism, because the facts re¬ 
quired for its treatment do not demand a world-wide mag¬ 
netic survey but may be derived from the operations of the 
47—Bull. Phil. Soc., Wash., Vol. 14. 
