SECOND REPORT-1832. 
31G 
plane polarization commenced. Fresnel, and all who have writ¬ 
ten on the subject, seem to have shrunk from this difficulty ; hut 
Mr. Airy saw that the two kinds of polarization must have some 
connecting link, and by the aid of theory and experiment he 
succeeded in discovering it. In place of the two rays in quartz 
consisting of plane polarized light, as was universally believed, 
Mr, Airy has shown that they both consist of elliptically po¬ 
larized light, the greater axis of the ellipse for the one ray be¬ 
ing in the principal plane of the crystal, and the greater axis 
of the other perpendicular to that plane. One of the rays he 
found to be right-handed elliptically polarized, and the other 
left-handed elliptically polarized. The proportion of the axes 
of the ordinary ray is more nearly one of equality than the pro¬ 
portion of the axes of the extraordinary ray, each proportion 
being one of equality when the direction of the ray coincides 
with the axis, and becoming more inequal with the inclination 
according to a law not yet discovered. The results calculated 
from the theory are in perfect accordance with those which Mr. 
Airy has obtained from very nice and difficult experiments ; so 
that we may regard this beautiful and singular property of the 
two rays of quartz as perfectly established. 
Mr. Airy has still more recently discovered a remarkable 
modification of Newton’s rings, when they are produced by a 
lens laid upon a polished metallic surface. This modification 
possesses much interest when considered only as a detached 
fact; but its importance is greatly enhanced by its direct bear¬ 
ing upon the two rival theories of light. On the Newtonian 
hypothesis the colours of thin plates are produced solely by the 
light reflected from the second surface of the plate; whereas, 
according to the undulatory hypothesis, they depend on the in¬ 
terference of the light reflected at the second surface, with the 
light reflected at the first surface. Hence, if we can by any 
means destroy the light reflected at the first surface, the rings 
ought to vanish, according to the undulatory hypothesis; while 
they ought still to appear, according to that of Newton. Mr. 
Airy conceived the happy idea of using polarized light, which 
was freely reflected from the second surface, while it was inca¬ 
pable of being reflected from the first; and upon trying the ex¬ 
periment, he found that the rings disappeared,—a result which 
he regards as “ perfectly inexplicable on any theory of emis¬ 
sion, and as affording satisfactory evidence that the rings are 
produced by interference only.” We have no hesitation in ad¬ 
mitting that this experiment is inexplicable on the Newtonian 
hypothesis of fits, and that the action of the two reflected pen¬ 
cils, either on each other or on the retina, is necessary to the 
