494 
ARTICLE XVII. 
Remarks on the Polarization of Light by Reflexion, especially by 
doubly refracting bodies, with an abstract of Mr. MacCullagh’s 
Treatise on the same sulject. By A. SEEBECK. 
[From Poggendorff’s Annalen, vol. xxxviii. No. 6, 1836.] 
AS is well known, Fresnel by his theory of double refraction 
was led to the view that in polarized light the vibrations of the 
zether take place at right angles or perpendicular to the plane of 
polarization. With this idea he and others developed formule 
for the intensity of the reflected light*. In so doing he added 
the two following premises:—1st, that in the two media, on the 
surfaces of which the reflection and refraction occur, the zther 
has the same elasticity, but a different density; 2nd, the dislo- 
cations of the particles of zther parallel to the surface of sepa- 
ration are equal in both media. On these suppositions (pre- 
serving the former signs), the amplitude of a ray which before 
reflexion was polarized parallel to the plane of polarization was 
sin («—7?) 
~ sin @+7) 
tan (i—7') | 
~ tan (i +7)’ 
But since it has been shown by Cauchy and Neumann, from 
the more strict theories of double refraction, that the vibra- 
tions must be considered as parallel to the plane of polariza- 
tion, the above formulz must be inverted, the second applying 
to the first and the first to the second case, whence they 
are no longer in accordance with experience. This difficulty 
however is removed by admitting that the zther possesses the 
same density in both media, but different elasticity instead of 
the supposition expressed in 1, and preserving the auxiliary hy- 
pothesis 2. For as the masses of ether in motion in the two me- 
dia are now in the relation of sin i cos 7: sin 7! cos 7, according 
to the law of active forces, we have 
, that of one polarized in a perpendicular plane was 
these formula were confirmed by observation. 
sin icosi (1—v*) = sin? cos? .u*. 
* Ann. de Chimie et de Phys. tome xlvi. 
