Another curious feature is that in the southern hemisphere the
direction of the motion is reversed, although its general
character remains the same. The pointing deviates towards the west
in the morning, then rapidly moves towards the east until about
two o'clock, after which it slowly returns to its original
direction.
The dip of the needle goes through a similar cycle of daily
changes. In northern latitudes it is found that at about six in
the morning the dip begins to increase, and continues to do so
until noon, after which it diminishes until seven or eight o'clock
in the evening, when it becomes nearly constant for the rest of
the night. In the southern hemisphere the direction of the
movement is reversed.
When the pointing of the needle is compared with the direction of
the moon, it is found that there is a similar change. But, instead
of following the moon in its course, it goes through two periods
in a day, like the tides. When the moon is on the meridian,
whether above or below us, the effect is in one direction, while
when it is rising or setting it is in the opposite direction. In
other words, there is a complete swinging backward and forward
twice in a lunar day. It might be supposed that such an effect
would be due to the moon, like the earth, being a magnet.
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