DISTRIBUTION OF THE EARTH’S MAGNETISM. 
519 
in the prosecution of these researches, 
and has proposed to obtain for them the 
national assistance. To call the atten- 
tion therefore of the scientific world, in 
a greater degree, to the present condi- 
tion of our knowledge as to Terrestrial 
Magnetism, was the object of Captain 
Sabine’s Report in the present volume 
of these Transaction ; and this he has 
accomplished by presenting us with an 
elaborate abstract of the work which 
Professor Hansteen,of Copenhagen, had 
published upon that subject. 
This mathematician, in the year 1811, 
constructed a chart, in which were laid 
down, so far as could be ascertained the 
lines of eq ual variation and dip of the mag- 
netic needle in all parts of the world. It is 
curious to observe the degree of coinci- 
dence which exists between these 
lines representing the distribution of 
the magnetic force, and the isothermal 
lines by which Humboldt has expressed 
the distribution of heat over the earth’s 
surface ; and this apparent connexion, 
the cause of which remains a mystery, 
is calculated to stimulate our zeal for 
investigating the phenomena of both. 
Nor is it less interesting to trace in 
what degree these later observations 
appear to confirm the general conclu- 
sion arrived at by the celebrated Halley 
more than a century before. That 
astronomer had inferred, from a general 
review of all that was then known wdth 
regard to the variation and dip of the 
needle, that there must be two mag- 
netic axes ; whilst the gradual shifting 
of the line of no»variation from west to 
east, led him to propose the ingenious, 
though whimsical hypothesis, of a 
moveable globe existing in the interior 
of the earth we inhabit, actuated by 
the same forces as those which propel 
the hollow sphere surrounding it, and, 
like it, possessing a north and south 
magnetic pole. This interior globe, if 
it be supposed to move with somewhat 
less rapidity than the exterior shell, 
might, as he concieved, produce a 
gradual shifting of poles from east to 
west, and thus account forthe difference 
observed from time to time in the posi- 
tion of the magnetic axes. 
Now the researches of Professor 
Hansteen confirm the existence of two 
magnetic axes, though they led him to 
discard the hypothesis by which Hal- 
ley accounted for their progressive shift- 
ing, which, indeed, the recently-dis- 
covered connexion between Electricity 
and Magnetism gives us hopes of ex- 
plaining more satisfactorily, as has been 
shown by Professor Christie in the Re- 
port read by him at our third meeting. 
Since the publication, however, of 
the great work to which his Magnetic 
Chart is appended, Professor Hansteen, 
aware of the mystery which still over- 
hangs the subject, has been zealously 
employed in attempting to remove it, 
by ascertaining the present state and 
progressive change of the magnetic 
forces. He has accordingly employed 
himself in making observations on the 
line of no variation, or, as he prefers to 
call it, the line of convergence which 
passes through Siberia ; and, by a for- 
tunate concurrence of circumstances, 
the north-western expedition lately un- 
dertaken by British navigators, has af- 
forded the means of obtaining, at the 
very same time, corresponding ones on 
the similar line, which extends from 
Hudson’s Bay through the United 
States of America. Thus the position 
of these lines in these two most inter- 
esting localities, has been almost simul- 
taneously determined with an exact- 
ness before unequalled. 
In conjunction with Captain Sabine, 
Professor Lloyd, of Dublin, has con- 
tributed, in anotherway, at the instance 
of the Association, to extend our ac- 
quaintance with the empirical laws of 
this interesting department of science. 
This they have effected by determining 
the dip and variation of the magnetic 
needle in different parts of Ireland, 
which it was considered the more im- 
portant to ascertain, from the situation 
of that island in the most westerly point 
of Europe, at which observations could 
be instituted. 
The distribution of the earth’s mag- 
netism through this country was deter- 
mined by the above-named observers, 
first by a separate series of observations 
relating to the force of that portion of 
the magnetic influence which operates 
horizontally; secondly, by a similar 
series on the dip of the needle ; thirdly, 
by means of observations both on the 
dip and intensity of the magnetic force 
made at the same time and with the 
same instruments. 
It would occupy too much of the 
time of the Association, were I to 
attempt to point out, however briefly, 
the precautions adopted, andthe correc- 
