apollonius ( 200 bc) discussed evolutes in book v of his "conics". however, huygens is sometimes credited with being the first to study them (1673). huygens formulated his theory of evolutes sometime around 1659 to help solve the problem of finding the tautochrone curve, which in turn helped him construct an isochronous pendulum. this was because the tautochrone curve is a cycloid, and the cycloid has the unique property that its evolute is also a cycloid. the theory of evolutes, in fact, allowed huygens to achieve many results that would later be found using calculus.