The article Newton'sPrinciple?(Speiser 1983) serves to propagate the view—long generally held but certainly erroneous—that thePrincipia(Cajori 1969) contains a proof that ‘all conic sections are solutions of [Newton's] universal law of gravitation’ (p. 149). It stops short, however, of expressing the more extreme commonly held misapprehension that thePrincipiagives—as it fallaciously purports to do—an outline of a proof that inverse-square force implies conic-section orbit; for the article goes on to say that only Johann Bernoulli succeeded in proving that the conic sections are the only solutions.