freely in brackets attached to the side of a pole.  The bottom end of the rod is pointed to engage with a nick in a bearer, in which it moves with but little friction.  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.  Or the rod may be built up of wooden rods, well painted, alternating with brass at the points where the brackets are.

[Illustration:  Fig. 156.—­Elevation and plan of vane.]

The Bevel Gearing.—­Two brass bevel wheels, about 1 inch in diameter, and purchasable for a couple of shillings or less, should be obtained to transmit the vane movements to the dial arrow.  Grooved pulleys, and a belt would do the work, but not so positively, and any slipping would, of course, render the dial readings incorrect.  The arrow spindle (of brass) turns in a brass tube, driven tightly into a hole of suitable size bored through the centre of the post (Fig. 157).  It will be well to fix a little metal screen over the bevel gear to protect it from the weather.

[Illustration:  Fig. 157.—­Details of bevel gear and arrow.]

The Dial—­This is made of tinned iron sheet or of 1/4-inch wood nailed to 1/2-inch battens.  It is held up to the post by 3-inch screws passing through front and battens.  At the points of contact, the pole is slightly flattened to give a good bearing; and, to prevent the dial being twisted off by the wind, strip iron or stout galvanized wire stays run from one end of a batten to the other behind the post, to which they are secured.

The post should be well painted, the top protected by a zinc disc laid under the top bracket, and the bottom, up to a point 6 inches above the ground level, protected by charring or by a coat of boiled tar, before the dial and the brackets for the vane rod to turn in are fastened on.  A white dial and black arrow and letters will be most satisfactory against a dark background; and vice versa for a light background.  The letters are of relatively little importance, as the position of the arrow will be sufficient indication.