He produced stationary waves with light polarized at an angle of 45 deg.,[22] and established that, when light is polarized in the plane of incidence, the fringes persist; but that, on the other hand, they disappear when the light is polarized perpendicularly to this plane.

If it be admitted that a photographic impression results from the active force of the vibratory movement of the ether, the question is, in fact, completely elucidated, and the discrepancy is abolished in Fresnel's favour.
[Footnote 22: That is to say, he reflected the beam of polarized light by a mirror placed at that angle.

See Turpain, _Lecons elementaires de Physique_, t.ii.p.311, for details of the experiment .-- ED.] M.H.Poincare has pointed out, however, that we know nothing as to the mechanism of the photographic impression.

We cannot consider it evident that it is the kinetic energy of the ether which produces the decomposition of the sensitive salt; and if, on the contrary, we suppose it to be due to the potential energy, all the conclusions are reversed, and Neumann's idea triumphs.
Recently a very clever physicist, M.Cotton, especially known for his skilful researches in the domain of optics, has taken up anew the study of stationary waves.

He has made very precise quantitative experiments, and has demonstrated, in his turn, that it is impossible, even with spherical waves, to succeed in determining on which of the two vectors which have to be regarded in all theories of light on the subject of polarization phenomena the luminous intensity and the chemical action really depend.