The vertical windmill (for information on Vertical Axis Windmills click here) consists of a strong shaft, or axis, inclining a little upwards from the horizon, with four long yards, or arms, fixed to the highest end, perpendicular to the shaft, and crossing each other at right angles. Into these arms are mortised several small cross-bars, and to them are fastened two, three, or four, long bars, running in a direction parallel with the length of the arms; so that the bars intersect each other, and form a kind of lattice work, on which a cloth is spread to receive the action of wind. These are called the sails, and are in the shape of a trapezium, usually about nine yards long and two wide.
As the direction of the wind is very uncertain, and perpetually changing, it becomes necessary to have some contrivance for bringing the windshaft and sails into a position proper for receiving its impression. To effect this, two methods are in general use: the one called the post-mill; the other the smock-mill.
In the post-mill it is accomplished by driving perpendicularly into the earth the trunk of a strong tree, that is held securely upright by several oblique braces, which extend from a platform on the ground to the middle of the tree, leaving 10 or 12 feet of the upper part free from the braces. The part thus left free from obstruction is rounded, and made to pass through a circular collar, formed in the flooring of the lower chamber, and to enter into a socket fixed into the flooring of the upper chamber, and to one of the strongest cross-beams, which must sustain the whole weight of the mill-house, so that, by means of a pivot, or gudgeon, fastened on that part of the post which enters into the socket, the whole machine can turn ubout horizontally to face the wind.
A strong framing, united by joints to the back part of the mill-house, descends a sloping direction till it touches the ground : the bottom of it is very heavy, and is fastened by cords to some short posts that are driven in a circle, at regular intervals round the mill, to prevent the mill from turning about at every sudden squall. This framing is furnished with steps to serve as a ladder of ascent or descent. At the bottom of it a rope is fastened, and carried thence in an inclined position to the top of the mill, where, by a lever or tackle of pullies, it can be shortened so as to raise the framing from the ground, and then by pushing against it, in the manner of a lever, the whole mill may be turned in any required direction. To obtain more force, a small capstan is often provided to draw a rope fixed to the end of the ladder : this capstan is moFable,and can be fastened at pleasure to anyone of the posts.
The internal mechanism of a post-mill is exhibited in fig. 123 above. WXY the upper chamber ; X Y Z the lower one ; A B the shaft, or axis, with the wheel G, moving round in order of the letters that describe the sails CDEF, giving motion to the lantern H, and its spindle IK; L M is a bridge to support the said spindle ; and N and O P are beams to sustain the bridge.
The top mill-stone Q is the only one that moves, and a fixed at the spindle I K by a piece of iron, called the rynd, let in at the lower span of the stone; the lower mill-stone R, is somewhat larger than the other. The corn is put into the hopper S, and runs from thence along the spout; the spindle I K, being square, shakes in its revolutions the spout T, and causes the corn to fall through the hole V between the stones, whhere it is ground; the flour then passes through the tunnel, and is badly deposited in the chest ; d e is a string going round the pin d, and serving to draw the spout nearer to, or farther from, the spindle I K, that ibe corn may be made to run out either faster or slower, according to the velocity of the wind ; fg a,nd Ai are levers, whose centres of motion are f and m. By bearing down the end rh, g is raised, which raises the perpendicular N O, the perpendicular raises the cross-beam O P, the crossbeam the bridge L AI and the spindle I K, together with the upper Q, so that the stones can be set at any required distance and rt.
The torn b drawn up to the top of the mill by means of a rope rolled about the uis A B ; q ? is a ladder for ascending to the higher part of the mill. A gripe of pliable wood is fixed at one end, and at the other tied to the lever ir, movable about at w, which being pressed down stops the motion of the mill at pleasure. When the wind is great, the sails are only in pan, or on one side covered, and sometimes only one-half of two opposite sails. The same shaft can have another cog-wheel fixed to the fed B, with trundle and mill-stones similar to those already described : by which means the shaft can turn two pair of stones at once ; and when one pair only is wanted to grind, the lantern H and spindle IK are taken out from the other.
The other method of bringing the windshaft and sails into a position proper for receiving the impression of the wind is by what is called the smock-mill. This mill is more expensive in the construction, and more decidedly advantageous, as it can be made of any required dimensions. It is built in the form of a round turret, having at the top of it a wooden ring with a groove in it, furnished with a number of brass truckles, kept equi-distant from each other by their centre pins being fixed into a circular hoop. Into this groove the framing of the upper or movable part of the mill, which is called the head, or cap, enters, and a very slight power is alone sufficient to turn it about that the sails may receive the action of the wind. The head or cap is very ingeniously contrived to turn itself about whenever the wind changes, by a small pair of sails, or fans, fixed up in a frame that projects from the back part of the head.