Mathematical Instruments
Book VIII. Ch. VIII.

Of the Construction of an Instrument, shewing on what Point of the Compass the Wind blows, without going out of one’s Room.

You must affix to the Ceiling, Mantle-Tree, or Wall of a Room, a Circle divided into 32 equal Parts, for the 32 Points of the Compass, so that the North and South Points thereof exactly answer to the meridian Line, which may be easily done by a Compass. Then there must be a Hand made moveable about the said Circle, and this Hand must be turned about by an upright Axle-Tree, which may be turned round by the least Wind blowing against the Fane at the Top thereof, above the Roof of the House.

But to explain this more fully, consult Fig. 17. The Wind turning the Fane AB (which ought to be of Iron), fixed to the Top of the Axle-Tree CD, turns this Axle-Tree, which is placed upright, and sustained towards the Top by the horizontal Plane EF, which is a Piece of Iron fastened to some convenient Place for holding up the Axle-Tree. And at the Bottom of the said Axle-Tree is placed a Steel Square GH, having a shallow small Hole D made therein for the Point of the Axle-Tree, which ought to be of tempered Steel for the Axle-Tree to stand in, and move with the least Wind. The Pinion IK must have 8 equal Teeth for the 8 principal Winds. The Teeth of this Pinion take into the Teeth of the Wheel ML, whole Number are 16 or 32, according to the Points denoted upon the Circle YZ; and so this Wheel is turned about by the Fane, as also it’s Axis PQ, which being placed horizontally, goes thro’ the Wall T at right Angles to it, as also to the Circle of Winds YZ, fixed to the Wall. The Hand R shewing which way the Wind blows, is fixed to the End of this Axle-Tree PQ, and turns along with it; and the Names of the Winds must be distinguished by Capital Letters, as on Compass Cards.

By the Disposition of the whole Instrument it is easy to perceive, that when the Wind turns the Fane AB, this likewise turns the Axle-Tree CD, which at the same Time turns the Pinion IK, and the Pinion IK the Wheel LM, and this the Axis QP, and QP the Hand. And so you may see which way the Wind blows, without going out of the Room.