areful study of the magnetic force
all over the country. It is found that there is a line running nearly
north and south through the Middle States along which there is no
variation of the compass. To the east of it the variation of the north
pole of the magnet is west; to the west of it, east. The most rapid
changes in the pointing of the needle are towards the northeast and
northwest regions. When we travel to the northeastern boundary of Maine
the westerly variation has risen to 20 degrees. Towards the northwest
the easterly variation continually increases, until, in the northern
part of the State of Washington, it amounts to 23 degrees.

When we cross the Atlantic into Europe we find the west variation
diminishing until we reach a certain line passing through central
Russia and western Asia. This is again a line of no variation. Crossing
it, the variation is once more towards the east. This direction
continues over most of the continent of Asia, but varies in a somewhat
irregular manner from one part of the continent to another.

As a general rule, the lines of the earth's magnetic force are not
horizontal, and therefore one end or the other of a perfectly suspended
magnet will dip below the horizontal position. This is called the "dip
of the needle." It is observed by means of a brass circle, of which the
circumference is marked off in degrees. A magnet is attached to this
circle so as to form a diameter, and suspended on a horizontal axis
passing through the centre of gravity, so that the magnet shall be free
to point in the direction indicated by the earth's lines of magnetic
force. Armed with this apparatus, scientific travellers and navigators
have visited various points of the earth in order to determine the dip.
It is thus found that there is a belt passing around the earth near the
equator, but sometimes deviating several degrees from it, in which
there is no dip; that is to say, the lines of magnetic force are
horizontal. Taking any point on this belt and going north, it will be
found that the north pole of the magnet gradually tends downward, the
dip constantly increasing as we go farther north. In the southern part
of the United States the dip is about 60 degrees, and the direction of
the needle is nearly perpendicular to the earth's axis. In the northern
part of the country, including the region of the Great Lakes, the dip
increases to 75 degrees. Noticing that a dip of 90 degrees would mean
that the nor