(127) The arrangement adopted by Messrs. Howard and Bullough has the central idea of the employment of inclined surfaces, by withdrawing one of which the other can be lowered. It is shown in front elevation in Fig. 60 and in section in Fig. 61. The fixed bend has formed on one side of it a broad flange, which is turned to a true circle on its upper edge. Upon this a segment of a ring A is placed, which can be slid in or out by means of the screw B and lock nuts. The back nut is riveted to the index disc =E=, which is divided into 36 spaces, the front lock nut securing the arrangement after setting. In front of the dial plate =E= an indicator finger =D= is fitted, which points out any alteration of the circular dial plate =E=. Upon the upper surface of the ring =A= a second ring =C= of a smaller section is placed. =C= is accurately turned on its inner side to correspond with the inclination of the upper surface of =A=, and on its outer edge is horizontal, so as to form a course for the end of the flat. The ring =C= is pressed down upon =A= by the weight of the chain of flats as they pass over it. The action of this mechanism is easily understood. By withdrawing the segmental ring =A=, by means of the screw =B=, the flats are lowered, the degree of their depression being sufficient to preserve the necessary distance between their wire teeth =G= and those =F= upon the cylinder =H=. The adjustment can be made in either direction, and the graduation of the dial =E= enables it to be finely made. In this case also, as shown in Fig. 55, the gap at the end of the cylinder is closed by bringing the flange of the fixed bend close to the edge of the cylinder.
(128) In Figs. 62 and 63 a plan invented by Mr. Thomas Knowles, of Bolton, and made by Messrs. John Tatham Limited is illustrated. This consists of the employment of a wedge-shaped segmental ring, which rests upon the upper edge of the fixed bend, and can be drawn along it by means of the screw shown. The ring is pierced by a number of holes of decreasing diameter, and a small slit is made through the web left between the lower part of the hole and the inner surface of the ring. The latter is thus rendered easily flexible, and the mere weight of the flats is sufficient to make it accommodate itself to its supporting surface. The ring is shaped so that the inner edge forms part of a spiral curve, shown diagrammatically in Fig. 63, and with its outer edge levelled so as to bear the flat. In like manner the edge of the fixed bend is shaped to the spiral curve, both of these being obtained by the use of a circular milling machine fitted with the necessary shaping mechanism. The spiral curve to which the two surfaces are formed would, if continued far enough, terminate in the centre of the cylinder, so that if it were possible to traverse the ring far enough it would actually cross that point. The action of setting this mechanism is simple. The ring is drawn downwards by the screw, and its outer edge thus moves nearer the centre of the cylinder to an extent corresponding with that of its traverse. Any adjustment desired can thus be given in either direction.