Haussmann applies circa 1801 the spherical trigonometry to crystals.

Wollaston invented before 1810 the refexion optical goniometer.

Towards 1810 Arago studied the rotatory polarization of quartz.

Biot, realized circa 1810 his studies of crystal optics and was interested in the optically uniaxial and biaxal crystals.

The great work in the field of crystal optics made by Fresnel circa 1820 lead to the definition of the indexes ellipsoid .