Slider 1 moves along fixed guides p-p and is connected by turning pair A to link 3. Wheel 2 rotates about axis B-B. When slider 1 moves along guides p-p, wheel 2, cutting into the surface of the drawing with its sharp edge, rolls along straight line AK. The envelope of the successive positions of straight line AK is a tractrix of Huygens with the equation a+sqrt(a²-y²)=y*e^((x-sqrt(a²-y²))/a) where a=A͞K; e = base of natural logarithms.
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