Vari\'{e}t\'{e}s de type Togliatti
  The Del Pezzo surface S\_6 obtained by blowing up the projective plane along three points (non aligned) has the following nice property : its osculating hyperplanes have a common point. For that reason S\_6 is also called Togliatti surface. In this paper we give two explanations of this fact. After what we obtain two different families of varieties with an analogous property. 
Jean Vall\`es (LMA-Pau)