  We are interested in the normal class of an algebraic hypersurface Z of the
complex projective space P^n, that is the number of normal lines to Z passing
through a generic point of P^n. Thanks to the notion of normal polar, we state
a formula for the normal class valid for a general hypersurface Z of P^n. We
give a generic result and we illustrate our formula with examples in P^n. We
define the orthogonal indidence variety and compute the Schubert class of the
variety of projective normal lines to a surface of P^3 in the Show ring of
G(1,3). We complete our work with a generalization of Salmon's formula for the
normal class of a Plucker curve to any planar curve with any kind of
singularity.
