Fig. 1022. Cyclograph for describing circular arcs in drawings where the centre is inaccessible. This is composed of 3 straight rules. The chord and versed sine being laid down, draw straight sloping line, from ends of former to top of latter; and to these lines lay 2 of the rules crossing at the apex. Fasten these rules together, and another rule across them to serve as a brace, and insert a pin or point at each end of chord to guide the apparatus, which, on being moved against these points, will describe the are by means of pencil in the angle of the crossing edges of the sloping rules.

Fig. 1023. Another cyelograph. The elastic arched bar is made half the depth at the ends that it is at the middle, and is formed so that its outer edge coincides with a true circular are when bent to its greatest extent; 3 points in the required are being given, the bar is bent to them by means of the screw, each end being confined to the straight bar by means of a small roller.

Fig. 1024. Instrument for describing pointed arches. Horizontal bar is slotted and fitted with a slide having pin for loop of cord. Arch bar of elastic wood is fixed in horizontal at right angles. Horizontal bar is placed with upper edge on springing line. and back of arch bar ranging with jump of opening, and the latter bar is bent till the upper side meets apex of arch, fulcrum-piece at its base ensuring its retaining tangential relation to jamb; the pencil is secured to arched bar at its connection with cord.

Fig. 1025. Centrolinead for drawing lines toward an inaccessible or inconveniently distant point; chiefly used in perspective. Upper or drawing edge of blade and back of movable legs should intersect centre of joint. Geometrical diagram indicates mode of setting instruments, legs forming it may form unequal angles with blade. At either end of dotted line crossing central, a pin is inserted vertically for instrument to work against. Supposing it to be inconvenient to produce the convergent lines until they intersect, even temporarily, for the purpose of setting the instrument as shown, a corresponding convergence may be found between them by drawing a line parallel to and inward from each.

Fig. 1026. P. Dickson's device for converting an oscillating motion into intermittent circular, in either direction. Oscillating motion communicated to lever A, which is provided with 2 pawls B and C, hinged to its upper side, near shaft of wheel D. Small crank E on upper side of lever A is attached by cord to each of pawls, so that when pawl C is let into contact with interior of rim of wheel D, it moves in one direction, and pawl B is out of gear. Motion of wheel D may be reversed by lifting pawl C, which was in gear, and letting opposite one into gear by crank E.

Fig. 1027. Proportional compasses used in copying drawings on a given larger or smaller scale. The pivot of compasses is secured in a slide which is adjustable in the longitudinal slots of legs, and capable of being secured by a set screw; the dimensions are taken between one pair of points and transferred with the other pair, and thus enlarged or diminished in proportion to the relative distances of the points from the pivot. A scale is provided on one or both legs to indicate the proportion.

Fig. 1028. Buchanan and Righter's slide-valve motion. Valve A is attached to lower end of rod B, and free to slide horizontally on valve-seat. Upper end of rod B is attached to a pin, which slides in vertical slots, and a roller C, attached to the said rod, slides in 2 suspended and vertically adjustable arcs D. This arrangement is intended to prevent the valve from being pressed with too great force against its seat by the pressure of steam, and to relieve it of friction.

Fig. 1029. Trunk-engine used for marine purposes. The piston has attached to it a trunk, at the lower end of which the pitman is connected directly with the piston. The trunk works through a stuffing box in cylinder-head. The effective area of the upper side of the piston is greatly reduced by the trunk. To equalize the power on both sides of piston, high-pressure steam has been first used on the upper side, and afterwards exhausted into and used expansively in the part of cylinder below.

Fig. 1030. Oscillating piston engine. The profile of the cylinder A is of the form of a sector. The piston B is attached to a rock-shaft C, and steam is admitted to the cylinder to operate on one and the other side of piston alternately, by means of a slide-valve D, substantially like that of an ordinary reciprocating engine. The rock-shaft is connected with a crank to produce rotary motion.

Fig. 1031. Root's double-quadrant engine. This is on the same principle as Fig. 1030; but 2 single-acting pistons B, B, are used, and both connected with one crank D. The steam is admitted to act on the outer sides of the 2 pistons alternately by means of one induction-valve a, and is exhausted through the space between the pistons. The piston and crank connections are such that the steam acts on each piston during about 2/3 revolution of the crank, and hence there are no dead-points.

Fig. 1032. One of the many forms of rotary engine. A is the cylinder having the shaft B pass centrally through it. The piston C is simply an eccentric fast on the shaft, and working in contact with the cylinder at one point. The induction and eduction of steam take place as indicated by arrows, and the pressure of the steam on one side of the piston produces its rotation and that of the shaft. The sliding abutment D, between the induction and eduction ports, moves out of the way of the piston to let it pass.

Fig. 1033. Another form of rotary engine, in which there are 2 stationary abutments D, D, within the cylinder; and the two pistons A, A, in order to enable them to pass the abutments, are made to slide radially in grooves in the hub C of the main shaft B. The steam acts on both pistons at once, to produce the rotation of the hub and shaft. The induction and eduction are indicated by arrows.