Fig. 1034. Bisecting gauge. Of 2 parallel cheeks on the cross-bar one is fixed and the other adjustable, and held by thumb-screw. In either cheek is entered one of 2 short bars of equal length, united by a pivot, having a sharp point for marking. This point is always in a central position between the cheeks, whatever their distance apart, so that any parallel-sided solid to which the cheeks are adjusted may be bisected from end to end by drawing the gauge along it. Solids not parallel-sided may be bisected in like manner, by leaving one cheek loose, but keeping it in contact with solid.

Fig. 1035. Self-recording level for surveyors, consists of a carriage, the shape of which is governed by an isosceles triangle, having horizontal base. The circumference of each wheel equals the base of the triangle. A pendulum, when the instrument is on level ground, bisects the base; and when on an inclination, gravitates to right or left from centre accordingly. A drum, rotated by gearing from one of the carriage wheels, carries sectionally ruled paper, upon which pencil on pendulum traces profile corresponding with that of ground travelled over. The drum can be shifted vertically to accord with any given scale; and horizontally, to avoid removal of filled paper.

Fig. 1036. A device for assisting the crank of a treadle motion over the dead-centres. The helical spring A has a tendency to move the crank B in direction at right angles to dead-centres.

Fig. 1037. Continuous circular motion into a rectilinear reciprocating. The shaft A, working in a fixed bearing D, is bent on one end, and fitted to turn in a socket at the upper end of a rod B, the lower end of which works in a socket in the slide C. Dotted lines show the position of the rod B and slide, when the shaft has made 1/2 revolution from the position shown in bold lines.

Fig. 1038. Continuous circular motion converted into a rocking motion. Used in self-rocking cradles. Wheel A revolves and is connected to a wheel B, of greater radius, which receives an oscillating motion, and wheel B is provided with two flexible bands C, D, which connect each to a standard or post, attached to the rocker E of the cradle.

Fig. 1039. Boot's double-reciprocating or square piston engine. The cylinder A of this engine is of oblong square form, and contains 2 pistons B and C, the former working horizontally, and the latter working vertically within it. The piston C is connected with the wrist a of the crank on the main shaft b. The ports for the admission of steam are shown black. The 2 pistons produce the rotation of the crank without dead-points.

Fig. 1040. Another rotary engine, in which the shaft B works in fixed bearings, eccentric to the cylinder. The pistons A, A, are fitted to slide in and out from grooves in the hub C, which is concentric with the shaft, but they are always radial to the cylinder, being kept so by rings (shown dotted), fitting to hubs on the cylinder-heads. The pistons slide through rolling packings A, A, in the hub C.

Fig. 1041. The indiarubber rotary engine, in which the cylinder has a flexible lining E of indiarubber, and rollers A, A, are substituted for pistons, said rollers being attached to arms radiating from the main shaft B. The steam acting between the india-rubber and the surrounding rigid portion of the cylinder presses the indiarubber against the rollers, and causes them to revolve around the cylinder and turn the shaft.

Fig. 1042. Holly's double-elliptical rotary engine. The 2 elliptical pistons geared together are operated upon by the steam entering between them in such manner as to produce their rotary motion in opposite directions.

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These rotary engines can all be converted into pumps.

Fig. 1043. Jonval turbine. The shutes are arranged on the outside of a drum, radial to a common centre, and stationary within the trunk or casing b. The wheel c is made in nearly the same way; the buckets exceed in number those of the shutes, and are set at a slight tangent instead of radially, and the curve generally used is that of the cycloid or parabola.

Fig. 1044. A method of obtaining a reciprocating motion from a continuous fall of water, by means of a valve in the bottom of the bucket which opens by striking the ground, and thereby emptying the bucket, which is caused to rise again by the action of a counterweight on the other side of the pulley over which it is suspended.

Fig. 1045. Overshot water-wheel.

Fig. 1046. Undershot water-wheel.

Fig. 1047. Breast-wheel. This holds intermediate place between overshot and undershot wheels; has float-boards like the former, but the cavities between are converted into buckets by moving in a channel adapted to circumference and width, and into which water enters nearly at the level of axle.

Fig. 1048. Horizontal overshot water-wheel.

Fig. 1049. A plan view of the Fourneyron turbine water-wheel. In the centre are a number of fixed curved shutes or guides A, which direct the water against the buckets of the outer wheel B, which revolves, and the water discharges at the circumference.

Fig. 1050. Warren's central discharge turbine, plan view. The guides a are outside, and the wheel b revolves within them, discharging the water at the centre.

Fig. 1051. Volute wheel, having radial vanes a, against which the water impinges and carries the wheel around. The scroll or volute casing b confines the water in such a manner that it acts against the vanes all around the wheel. By the addition of the inclined buckets c, c, at the bottom, the water is made to act with additional force as it escapes through the openings of said buckets.