Augustin Jean Fresnel

“ Yesterday I finally ascertained that the speed was non-uniform for the ordinary ray in crystals of two axes, as my theoretical ideas on double refraction told me in advance and in such a necessary manner that, if the result of the experiment had not been in conformity with this consequence, I would have been obliged to reject entirely my hypotheses on double refraction ”

“ From the beginning of 1820, Fresnel had caused M. Soleil Sr. to manufacture a prototype large polygonal lens intended to form one of the panels of a rotating dioptric drum. To illuminate these effectively, however, it was necessary to maintain a sufficiently voluminous and intense flame at their common focus — a problem that the inventor had managed to solve, in collaboration with Arago, by means of a nozzle with concentric wicks fed with oil by a clockwork mechanism ”

“ In the plane perpendicular to the midline, the rays with this polarization are designated by Fresnel as the "extraordinary" rays; this terminology takes the midline between the axes as analogous to the axis of a uniaxial crystal.↑ These laws are also known respectively as Biot's dihedral law and Biot's sine law ”