Apparatus for the optical determination of stresses

Claim 1

APPARATUS FOR MEASURING BIREFRINGENCES AND INTERNAL STRESSES IN A MATERIAL CAPABLE OF TRANSMITTING AND INTERNALLY REFLECTING LIGHT RAYS, SAID MATERIAL BEING IN THE FORM OF A PLATE WITH PARALLEL SURFACES, SAID APPARATUS BEING ADAPTED FOR MEASURING THE VALUES OF THE PRINCIPAL RECTANGULAR STRESSES IN SAID MATERIAL BY TWO OBSERVATIONS EFFECTED IN THE PRINCIPAL PLANES, SAID APPARATUS COMPRISING MEANS TO PROJECT IN A DIRECTION PERPENDICULAR TO THE UPPER SURFACE OF THE PLATE A BEAM OF POLARIZED LIGHT HAVING ITS PLANE OF POLARIZATION INCLINED WITH RESPECT TO THE PLANE OF INCIDENCE ON THE PLATE TO BE EXAMINED, A TRANSPARENT REFRINGENT BODY ADAPTED TO MAKE OPTICAL CONTACT WITH THE FIRST FACE OF THE PLATE, OPTICAL MEANS FOR DIVERTING THE POLARIZED BEAM TOWARD THE TRANSPARENT REFRINGENT BODY, THE POLARIZED LIGHT BEAM PASSING FROM THE TRANSPARENT REFRINGENT BODY THROUGH THE FIRST SUFACE OF THE PLATE WITHOUT DEVIATION AND PARTIAL REFLECTION AND PENETRATING OBLIQUELY INTO THE PLATE AT SUCH PREDETERMINED ANGLE WITH RESPECT TO THE NORMAL TO THE PLATE THAT SAID BEAM IS TOTALLY REFLECTED ON THE UNDER SURFACE OF THE SAID PLATE, THE TRANSPARENT REFRINGENT BODY BEING SO CONSTRUCTED AND ARRANGED THAT THE REFLECTED EMERGENT BEAM PASSES INTO SUCH BODY