Fig. 1094. A spiral wound round a cylinder to convert the motion of the wind, or a stream of water, into rotary motion.

Fig. 1095. Common windmill, illustrating the production of circular motion by the direct action of the wind upon the oblique sails.

Fig. 1096. Plan of a vertical windmill. The sails are so pivoted as to present their edges in returning toward the wind, but to present their faces to the action of the wind, the direction of which is supposed to be as indicated by the arrow.

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Fig. 1097. Common paddle-wheel for propelling vessels. The revolution of the wheel causes the buckets to press backward against the water, and so produce the forward movement of the vessel.

Fig. 1098. Screw-propeller. The blades are sections of a screw-thread, and their revolution in the water has the same effect as the working of a screw in a nut, producing motion in the direction of the axis, and so propelling the vessel.

Fig. 1099. Vertical bucket paddle-wheel. The buckets a, a, are pivoted into the arms b, b, at equal distances from the shaft. To the pivots are attached cranks c, c which are pivoted at their ends to the arms of a ring d, which is fitted loosely to a stationary eccentric e. The revolution of the arms and buckets with the shaft causes the ring d also to rotate upon the eccentric, and the action of this ring on the cranks keeps the buckets always upright, so that they enter the water and leave it edgewise without resistance or lift, and while in the water are in the most effective position for propulsion.

Fig. 1100. Brown and Level's boat-detaching hook. The upright standard is secured to the boat, and the tongue, hinged to its upper end, enters an eye in the lever, which works on a fulcrum at the middle of the standard. A similar apparatus is applied at each end of the boat. The hooks of the tackles hook into the tongues, which are secure until it is desired to detach the boat, when a rope attached to the lower end of each lever is pulled in such a direction as to slip the eye at the upper end of the lever from off the tongue, which, being then liberated, slips out of the hook of the tackle and detaches the boat.

Fig. 1101. Ordinary steering apparatus. Plan view. On the shaft of the hand-wheel there is a barrel, on which is wound a rope, which passes round the guide-pulleys, and has its opposite ends attached to the tiller, or lever, on top of the rudder; by turning the wheel, one end of the rope is wound on and the other let off, and the tiller is moved in one or the other direction, according to the direction in which the wheel is turned.

Fig. 1102. Capstan. The cable or rope wound on the barrel of the capstan is hauled in by turning the capstan on its axis by means of handspikes, or bars inserted into holes in the head. The capstan is prevented from turning back by a pawl attached to its lower part and working in a circular ratchet on the base.

Fig. 1103. Lewis, for lifting stone in building. It is composed of a central taper pin or wedge, with 2 wedge-like packing pieces arranged one on each side of it. The 3 pieces are inserted together in a hole drilled into the stone, and when the central wedge is hoisted upon it wedges the packing pieces out so tightly against the sides of the hole as to enable the stone to be lifted.

Fig. 1104. Tongs for lifting stones. The pull on the shackle which connects the 2 links causes the latter so to act on the upper arms of the tongs as to make their points press themselves against or into the stone. The greater the weight the harder the tongs bite.

Fig. 1105. Drawing and twisting in spinning cotton, wool, etc. The front drawing-rolls B rotate faster than the back ones A, and so produce a draught, and draw out the fibres of the sliver or roving passing between them. Roving passes from the front drawing-rolls to throstle, which, by its rotation around the bobbin, twists and winds the yarn on the bobbin.

Fig. 1106. Fan-blower. The casing has circular openings in its sides, through which, by the revolution of the shaft and attached fan-blades, air is drawn in at the centre of the casing, to be forced out under pressure through the spout.

Fig. 1107. Siphon pressure gauge. Lower part of bent tube contains mercury. The leg of the tube, against which the scale is marked, is open at top, the other log connected with the steam boiler or other apparatus on which the pressure is to be indicated. The pressure on the mercury in the one leg causes it to be depressed in that and raised in the other, until there is an equilibrium established between the weight of mercury and pressure of steam in one leg, and the weight of mercury and pressure of atmosphere in the other. This is the most accurate gauge known; but as high pressure requires so long a tube, it has given place to those which are practically accurate enough, and of more convenient form.

Fig. 1108. Mercurial barometer. Longer leg of bent tube, against which is marked the scale of inches, is closed at top, and shorter one is open to the atmosphere, or merely covered with some porous material. Column of mercury in longer leg, from which the air has been extracted, is held up by the pressure of air on the surface of that in the shorter leg, and rises or falls as the pressure of the atmosphere varies. The old-fashioned weather-glass is composed of a similar tube attached to the back of a dial, and a float inserted into the shorter leg of the tube, and geared by a rack and pinion, or cord and pulley, with the spindle of the pointer.