. Elements of technology :. sirable in tooth-ed wheels, as far as possible, to diminish friction, and to pro-duce uniformity of force and motion. A uniform motion maybe produced, if the form of the acting face of the teeth be acurve of the epicycloidal kind ; the outline of the teeth of onewheel being the curve which would be described by the revo-lution of a curve upon a given circle, while the outline of theteeth of the other wheel, is described by the same curve rollingwithin the circle. It may also be produced, if the teeth of onewheel be straight, circular, or of any regular figure whatev
. Elements of technology :. sirable in tooth-ed wheels, as far as possible, to diminish friction, and to pro-duce uniformity of force and motion. A uniform motion maybe produced, if the form of the acting face of the teeth be acurve of the epicycloidal kind ; the outline of the teeth of onewheel being the curve which would be described by the revo-lution of a curve upon a given circle, while the outline of theteeth of the other wheel, is described by the same curve rollingwithin the circle. It may also be produced, if the teeth of onewheel be straight, circular, or of any regular figure whatever;provided the teeth of the other wheel, be of a figure compound-ed of that figure and of an epicycloid. * For investigations relating to the teeth of wheels, see Camus on the Teethof Wheels, translated, London, 8vo. 1806 ;—Buchanan on Mill Work, chap,i. &,€.;—Brewsters Fergusons Lectures, vol. ii. p. 119;—Gregorys Mechan-ics, vol. ii. p. 451 ;—also a Treatise by Mr Blake, in SilUmans Journal, p. ELEMENTS OP MACHINERY. 231 Of two wheels which are unequal in size, the larger is calledthe wheel, and the smaller the pinion. The acting portions ofthe wheel are called teeth ; and of the pinion, more commonly,leaves. The name of lanterns is given to pinions with twoheads connected by cylindrical teeth, or trundles. In Fig. 4,the line joining the centresB and F of the wheel and pin-ion, is called the line of centres,and when this line is dividedinto two parts, ^F A and BA,which are to each other as thenumber of leaves in the pinionis to the number of teeth in thewheel; B A is called the primi-tive radius * of the wheel, andF A, the primitive radius of thepinion ; while the lines or dis-tances F f and B b, are called thetrue radii. The circles X AXand R A R are called the prim-itive circumferences, and by workmen, the pitch lines. Friction, to a certain extent, cannot be avoided, in teeth ofthe common kind, whose acting faces are at right angles w^iththe plane
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