Under the path of this piece is
a ring of equally spaced magnets, their number equaling that of, the
segments on the vane. Between arrow and magnets is the dial on which the
points are marked (Fig. 159).
Each segment is connected by a separate wire with the corresponding dial
magnet, and each of these, through a common wire and switch, with the other
terminal of the battery (Fig. 161).
In order to ascertain the quarter of the wind, the switch is closed. The
magnet which is energized will attract the needle to it, showing in what
direction the vane is pointing. To prevent misreading, the dial may be
covered by a flap the raising of which closes the battery circuit. A spring
should be arranged to close the flap when the hand is removed, to prevent
waste of current.
[Illustration: FIG. 160.--Another type of electric dial with compass
needle for pointer.]
The exactitude of the indication given by the arrow depends on the number
of vane segments used. If these are only four, a N. read- ing will be given
by any position of the vane between N.E. and N.W.; if eight, N. will mean
anything between N.
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