The boy's book of trades and the tools used in them

by Anonymous

In a breast wheel, the water has no previous fall, and therefore does not strike the floats at the bottom of the wheels, as in the undershot wheel, with an increased velocity. The breast wheel is therefore fixed in what is called a race, formed of stone or brick work, agreeing with the curvature of the wheel, and being thus let on from its own level, acts both by its weight and momentum, or movement. This wheel is unlike the undershot wheel, being close boarded round its circumference, like an overshot or balance wheel, the undershot wheel being always open; in short, it is a sort of bucket wheel; the buckets, however, being constructed differently from those of the overshot and balance wheels.

A tide-mill, as the name imports, is worked by the ebbing and flowing of the tide. Of these mills there are various kinds; first, those in which the water wheel turns one way when the tide is rising, and the other when it is falling; secondly, those in which the wheel turns the same way whether it is rising or falling; thirdly, those in which the wheel itself rises or falls as the tide flows or ebbs; and fourthly, those in which the axle of the water wheel is so fixed, that it shall neither rise nor fall; the rotary motion being still given to the wheel, whether it be partially or wholly immersed in the water.

All the machines for grinding corn and seeds are mills, whatever may be their particular application. One very common form is that of an iron machine, supported on four legs, having a winch handle on one side, a fly wheel on another, a hopper at the top, and a crushing apparatus in the centre. The grain or seed is put into the hopper, the winch handle is turned, the grain becomes crushed to powder, and falls out at the bottom of the apparatus. Sometimes the mill is made chiefly of wood, but with iron wheel and crushing apparatus. One kind of wheat mill, in addition to the usual mill apparatus, has a chest which acts as a flour-dressing machine. Some mills are adapted for crushing beans rather than seeds.

The crushing apparatus in mills is of two kinds, either one stone working round in contact with another, or two metallic surfaces, between which the substance is forced, but between which it cannot pass except in a fine state.

The millstones employed in grinding corn require to be made of a peculiar kind of stone. The greater proportion of our millstones are procured from a particular spot in Western Germany. At about ten miles from Coblentz is a small town called Andernach, the chief trade of which is in millstones, procured from the neighbouring quarries of Nieder Mendig. There are several quarries, averaging about fifty feet in depth, each quarry shaped like an inverted cone, down the sides of which the quarrymen descend by a spiral path. The quarrymen have to cut away through a superincumbent layer of soft porous stone, till they come to a layer of hard, blackish, heavy stone, regularly porous, and yielding sparks when struck with iron. This is the millstone, and requires good and well-prepared tools to work it; it is supposed to be a compact lava from some extinct volcano; and as there are fissures or gaps at intervals, these facilitate the separation of the stone into blocks suitable for millstones. All round the bottom of the conical cavities, the stone has been excavated in galleries or horizontal passages. The stones are brought to shape by means of hammers and chisels. A deep socket is cut through the middle of such stones as are intended for runners, or upper stones. The furrows on the surfaces of the stones are produced by means of a double-edged hammer, about 14 lbs. weight.

Windmills are of two kinds; in one the wind is made to act upon vanes or sails, generally four, which are disposed so as to revolve by that action in a plane which is nearly vertical; and in the other, the axis of revolution being precisely vertical, any point on the surface of a vane revolves in a horizontal plane. The former is called a vertical windmill, and the latter a horizontal windmill.

The building for a vertical windmill is generally a wall of timber or brickwork, in the form of a frustrum of a cone, and terminated above by a wooden dome, which is capable of revolving horizontally upon it. A ring of wood, forming the lower part of the dome, rests upon a ring of the same material at the top of the wall, and the surfaces in contact being made very smooth, the dome may easily be turned round upon the wall; and is prevented from sliding off by a rim which projects from it, and descends over the interior circumference of the lower ring. The dome in turning carries with it the windsails and their axle; and thus the wind sails may be adjusted to agree with the direction of the wind, or the plane in which the radii of the sails turn may be made perpendicular to that direction. The revolution is sometimes accomplished by the force of a man applied to a winch near the ground, but in general the wind itself is made to turn the dome or the mill by means of a set of small vanes, which are situated at the extremity of a long horizontal arm projecting from the dome, in a plane passing through the vertical shaft of the mill, and on the side opposite to the great sails.

A horizontal windmill is a great cylindrical frame of timber, which is made to revolve about an upright centre, and its convex surface is formed of boards attached in vertical positions to the upper and lower parts of the frame. The whole is enclosed in a fixed cylinder having the same upright centre as the other; this consists of a revolving screen or a number of boards, which are so disposed that in whatever direction the wind may blow, it may enter between them on one side only of a vertical plane, passing through the axis, and thus give motion to the interior cylinder. The effective power of the vertical windmill is, however, so much greater than that of the horizontal windmill, that the latter is now seldom constructed.