Vibration of Polarized Light in the Plane of Polarization. 125 



geneous regulus, which is forged with great ease. Its ductility 

 is almost unlimited, and its tenacity is as great as that of iron. 

 A nickel wire which requires 90 kilogrammes to break it, has 

 the same diameter as an iron wire which is broken by 60 kilo- 

 grammes. 



Cobalt is prepared in the same way. It is as ductile as nickel, 

 and more tenacious. Its tenacity is to that of nickel as 115 to 

 90. Cobalt is hence nearly twice as tenacious as iron. 



Silica is the most refractory body on which Denlle has ex- 

 perimentedj but even this he has succeeded in melting. 



XX. Polarized Light vibrates in the Plane of Polarization. 

 By C. H. A. HoLZMANN*. 



1. TF we take a diffraction grating with parallel slits, which, 

 J»- for the sake of shortness of expression, I will assume 

 shall stand vertical, and if upon this grating a horizontal pencil 

 of light be allowed to fall, the light will be spread out by diffrac- 

 tion in a horizontal direction. If the incident light be plane 

 polarized, we shall be able to decompose its vibrations into ver- 

 tical, which are thus parallel with the slit, and into horizontal. 

 The vertical vibrations will not be changed by diffraction ; the 

 horizontal ones, however, will ; they will be decomposable into 

 such as lie in the direction of any assumed diffracted ray, and 

 into such as are normal to this direction. The first will give 

 condensed waves in this direction, and will not be perceived as 

 light; the second, on the contrary, will proceed as transverse 

 waves in the direction of the diffracted ray, and, together with 

 the vertical vibrations proceeding in the same direction, will give 

 the diffracted light. 



The diffracted light has hence the same vertical, but another 

 and smaller component than incident light ; and the direction of 

 its vibration cannot therefore coincide with the direction of vibra- 

 tion of the incident light. It must be steeper than the latter. 



From this it is easy to determine the direction of vibration in 

 the diffracted light. If the direction of the incident ray of light 

 be normal to the surface of the diffraction grating, and if s be 

 the distance of an sether particle at the time / from its position 

 of equilibrium, then, under the assumption that transverse waves 

 only meet the grating, the vertical projection of s, if a be the 

 angle of the direction of vibration, or of s with the vertical, is 

 equal to 



$ cos a ; 



* Translated by Dr. E. Atkinsou from PoggendorfF's Avnalen, No. 11, 

 for 1856. 



