1851.| OF THE ROYAL INSTITUTION. 57 
curves, or lines of magnetic force, existing in the space around. 
These phrases have a high meaning, and represent the ideality of 
magnetism. They imply not merely the directions of force, which are 
made manifest when a little magnet, or a crystal, or other subject of 
magnetic action is placed amongst them, but those lines of power 
which connect and sustain the polarities, and exist as much when there 
is no magnetic needle or crystal there as when there is; having an 
independent existence analogous to (though very different in nature 
from) a ray of light or heat, which, though it be present in a given 
space, and even occupies time in its transmission, is absolutely insen- 
sible to us by any means whilst it remains a ray, and is only made 
known through its effects when it ceases to exist. The form of a 
line of magnetic force may vary exceedingly from a straight line to 
every degree of curvature, and may even have double and compli- 
cated curvatures impressed upon it. Its direction is determined by its 
polarity, the two changing together. Its powers are such, that a 
magnetic needle placed in it finds its place of rest parallel to it; a 
crystal of calcareous spar turns until its optic axis is transverse to it ; 
and a wire which is unaffected when moved in or along it, has an electric 
current evolved the instant that it passes across it: by these and by 
other means the presence of the magnetic line of force and its direc- 
tion are rendered manifest. 
The Earth is a great magnet: its power, according to Gauss, 
being equal to that which would be conferred if every cubic yard of 
it contained six one-pound magnets; the sum of the force therefore is 
equal to 8,464,000,000,000 000,000,000 such magnets. The dispo- 
sition of this magnetic force is not regular, nor are there any points 
on the surface which can be properly called poles: still the regions 
of polarity are in high north and south latitudes; and these are con- 
nected by lines of magnetic force (being the lines of direction) which, 
generally speaking, rise out of the earth in one (magnetic) hemi- 
sphere, and passing in varied directions over the equatorial regions 
into the other hemisphere, there enter into the earth to complete the 
known circuit of power. A free needle shows the presence and 
direction of these lines. In London they issue from the earth at an 
angle of about 69° with the horizon (being the dip or inclination) ; 
and the plane in which they rise forms an angle of 23° W. nearly 
with true north, giving what is called west declination. Where the 
dip is small, as at the magnetic equator, these lines scarcely rise out 
of the earth and pass but a little way above the surface ; but where it 
is large, as in northern or southern latitudes, they rise up at a 
greater angle, and pass into the distant realms of space, from 
whence they return again to the earth in the opposite magnetic hemi- 
sphere; thus investing the globe with a system of forces like that 
about an ordinary magnet, which wherever it passes through the atmo- 
sphere is subject to the changing action of its magnetic oxygen. 
There is every reason to believe that these lines are he/d in the earth, 
out of which they arise and by which they are produced, just as the 
