364 The Followers of Maxwell. 



The old question as to whether the light-vector is in, or at 

 right angles to, the plane of polarization* now presented itself 

 in a new aspect. The wave-front of an electric wave contains 

 two vectors, the electric and magnetic, which are at right angles 

 to each other. Which of these is in the plane of polarization ? 

 The answer was furnished by Fitz Gerald and Trouton,f who 

 found on reflecting Hertzian waves from a wall of masonry that 

 no reflexion was obtained at the polarizing angle when the 

 vibrator was in the plane of reflexion. The inference from this 

 is that the magnetic vector is in the plane of polarization of the 

 electric wave, and the electric vector is at right angles to the 

 plane of polarization. An interesting development followed in 

 1890, when 0. Wiener^ succeeded in photographing stationary 

 waves of light. The stationary waves were obtained by the 

 composition of a beam incident on a mirror with the reflected 

 beam, and were photographed on a thin film of transparent 

 collodion, placed close to the mirror and slightly inclined to it. 

 If the beam used in such an experiment is plane-polarized, and 

 is incident at an angle of 45, the stationary vector is evidently 

 that perpendicular to the plane of incidence; but Wiener 

 found that under these conditions the effect was obtained only 

 when the light was polarized in the plane of incidence ; so 

 that the chemical activity must be associated with the vector 

 perpendicular to the plane of polarization i.e., the electric 

 vector. 



In 1890 and the years immediately following appeared 

 several memoirs relating to the fundamental equations of 

 electro-magnetic theory. Hertz, after presenting the general 



* Cf. pp. 168 et sqq. 



f Nature, xxxix (1889), p. 391. 



\ Ann. d. Phys. xl (1890), p. 203. Cf. a controversy regarding the results ; 

 Comptes Rendus, cxii (1891), pp. 186, 325, 329, 365, 383, 456 ; and Ann. d. Phys. 

 xli (1890), p. 154 ; xliii(1891), p. 177; xlviii (1893), p. 119. 



Gott. Nach. 1890, p. 106; Aim. d. Phys. xl (1890), p. 577; Electric Waves 

 (English ed.), p. 195. In this memoir Hertz advocated the form of the equations 

 which Maxwell had used in his paper of 1868 (cf. supra, p. 287) in preference to 

 the earlier form, which involved the scalar and vector potentials. 



