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Appletons' cyclopaedia of applied mechanics: a dictionary of mechanical engineering and the mechanical arts . 18 GEARING. diameters of the other two. Thus every internal epicycloid is also an external one ; but the epitro-choids traced by points carried by these different describing circles, not on their circumferences, willnot be the same. In the diagram on the right, D is the centre of the large base-circle, within whichare shown two describing circles, the sum of their diameters equaling the diameter of D ; and the. same hypocycloid will be traced by therolling of cither of them within the
Appletons' cyclopaedia of applied mechanics: a dictionary of mechanical engineering and the mechanical arts . 18 GEARING. diameters of the other two. Thus every internal epicycloid is also an external one ; but the epitro-choids traced by points carried by these different describing circles, not on their circumferences, willnot be the same. In the diagram on the right, D is the centre of the large base-circle, within whichare shown two describing circles, the sum of their diameters equaling the diameter of D ; and the. same hypocycloid will be traced by therolling of cither of them within the out-er circle. In both these eases, if thecurve be traced in a given direction, thetwo circles by which it may be gener-ated will roll in opposite directions. The Epitrochoid.—It is evident thatthe marking-point carried by a rollingcircle, or other line, need not be in therolling line. Although, as above stated,the term epitrochoidal is applied in g< n-eral to all lines generated by marking-points so controlled, yit the name epi-trochoid is also specifically applied inthe ca-^e in which the point is carriedby one circle rolling upon another, andis not situated in the circumference. Ifit be outside the rolling circle, the curveis called a curtate epitrochoid, and islooped, as shown in Fig. 2107. If themarking-point be within the rolling cir-cle, as in Fig. 2108, the curve is waved,the marking-point never reaching thebase-circle, and is called jn-olalc. Theepicycloid is therefore, it will be seen,but a speci
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