Near the end is fixed a horizontal bevel-wheel,
engaging with a vertical bevel of equal size and number of teeth attached
to a short rod running through a hole in the post to an arrow on the other
side. Between arrow and post is room for a dial on which the points of the
compass are marked.
The construction of the apparatus is so simple as to call for little
comment. The tail of the vane is made of two pieces of zinc, tapering from
8 inches wide at the rear to 4 inches at the rod, to which they are clipped
by 4 screws and nuts. A stay soldered between them near the stern keeps the
broader ends a couple of inches apart, giving to the vane a wedge shape
which is more sensitive to the wind than a single flat plate. The pointer
also is cut out of sheet metal, and is attached to the tail by means of the
screws already mentioned. It must, of course, be arranged to lie in a line
bisecting the angle formed by the two parts of the tail.
[Illustration: FIG. 165--Wind vane with dial.]
The rod should preferably be of brass, which does not corrode like iron. If
the uppermost 18 inches or so are of 1/4-inch diameter, and assigned a
bracket some distance below the one projecting from the top of the pole,
the remainder of the rod need not exceed 1/8 to 5/32 inch in diameter, as
the twisting strain on it is small.
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