Variation
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Change; alteration.
In astronomy, a periodic irregularity in the motion of the moon owing to the disturbing action of the sun.
In magnetism, the declination of the magnetic needle from the true or geographical meridian; the angle which the magnetic meridian makes with the geographical meridian.
The variation of the magnetic needle is not constant. In 1663, in Paris, the compass needle pointed true north, previous to which year the variation had been easterly. From 1663 to 1814 the variation in Paris was westerly, increasing steadily until 1814, when it amounted to 22 1/2 deg. W, from which year it has steadily decreased, but is still westerly.
