  This is a survey article on two topics. The Energy E of knots can be obtained
by generalizing an electrostatic energy of charged knots in order to produce
optimal knots. It turns out to be invariant under Moebius transformations. We
show that it can be expressed in terms of the infinitesimal cross ratio, which
is a conformal invariant of a pair of 1-jets, and give two kinds of
interpretations of the real part of the infinitesimal cross ratio.
