Polarization in perfectly transparent Media. — 475 
sponding lines in the two bodies will be numerically equal but 
‘have opposite signs.* 
It follows ie if a body is pores in internal structure 
ith its own image by reflection, the value of ¢ (if not zero for 
ail directions) must be positive ‘for some directions and nega- 
tive for othe 
reflection of the other. This ae that the hyperboloids 
shall be right cylinders with conjugate rectangular hyperbo- 
las for bases. A crystal characterized dy suc prove 
kind from an ordinary uniaxial crystal, unless the ellipsoid (24) 
should approach very closely to a sphere. 
It is only in the very limited case described in the last para- 
graph that a medium which is identical in its internal struct- 
images vy reflection, ad have the property of circular polariza- 
tion, we on apply the itlowins general principles. 
medium has any axis ‘of symmetry, the ellipsoid or 
hyperboloi which Sie the values of g will have an axis 
in same directi If the medium a revolution of 
io ol 180° abo me any axis is quienes o the medium in 
its first position, the epee or hyperbolids will have an 
axis of revolution in that dir 
23. The laws of the sale a of light in plane waves, 
which Sees thus been derived from the single hypothesis that 
the disturbance by which light is transmitted consists of solen- 
oidal electrical fluxes, and which a ly to light of different 
colors and to the most general case of perfectly transparent 
and sensibly homogeneous media not subject to magnetic 
poe: are essentially those pagan are generally received as 
*The necessity of the opposite signs will perhaps appear most readily from 
the obuiseaueon that the direction of veletiien of the plane of polarization must 
be opposite in the two ies, 
here is no difficulty in conceiving of the constitution of a body which could 
have properties described above. Thus, we may imagine a body with mole- 
cules of a spiral form, of which one-half are right-handed and one rs eft- 
handed, and we may suppose that the motion te lectricity is opposed a less” 
resistance within them than without. If the axes of the hese mouilen 
are parallel to the axis of X, and those of the left-handed molecules to the axis of 
Y, their effects would counterbalance one another pep the se is par- 
allel to the axisof Z. But when the wave-norma’ a beam of linearly polar- 
ized light), is parallel to the axis of X, the an ea eg sales les oe gc peo 
i i i nee 
¢ The rotation of — pla ne of polarization chien is produced by ne er 
action has been discussed by Maxwell ( Treatise on Electricity and Magnetism, vol. 
ii, Chap. XX), and rs Rowland (Amer. Journ. Math., vol. i, p. 107). 
