CIRCULAR POLARIZATION OF LIGHT. 81 
larger now becomes the smaller one, and vice versd. With increasing 
excentricity the elliptic vibrations, which are perpendicular to the initial 
ones, pass directly over them. During all this process, the direction of 
the vibrations did not change; supposing it to have been from left to 
right, it remained so. When however the second rectilineal vibration 
opens into an elliptic one, and the direction of the motion has become 
inverted, the vibration now takes place from left to right, supposing it to 
have been before from right to left. The vibrations then return through ~ 
circular again into the initial vibrations. 
The light proceeding from the cube was now circularly analysed, by 
means of the interposition of a lamina of mica f of a proper thickness be- 
tween the plate of Iceland spar and the analysing prism. The axis of 
this lamina lay so that the segments of the arcs were removed from the 
central point to the first and third quadrants. When the cube was yet 
unheated, its action was thus in direct opposition to its action in the first 
degree of its heating. When, proceeding from this point, the rings with- 
out the cross and with the black spot in the centre were formed, this 
spot, on the heat being increased, divided itself into two, which removed 
themselves from the centre into the second and fourth quadrants, and 
after having passed through the figure in the circular light, closed into 
a circle with the ares proceeding from the first and third quadrants, so as 
to produce the system of rings with a bright centre, which would have 
been obtained at the very beginning by turning the polarizing prism 90°. 
The ares, approaching nearer to the central point from the first and third 
quadrants, formed then the opposite circular figure, and united them- 
selves at last in the centre into a black spot, whilst all the ares closed 
themselves into circles. Inthisprocess, the phenomena before described 
of the linear analyses will again be easily recognised as a conditional ele- 
ment, without the necessity of particularly describing the alteration in 
form of the rings before they disunite into separate arcs. 
To make circular light incident, is simply to add to the difference of 
; 2n—-1 
a oF 
undulations; that is to say, to alter the starting-point of the ex- 
phases produced by the heated cube a constant quantity, viz. 
2n+1 
4 
periment. Having therefore inserted the lamina of micag between the 
polarizing prism and the heated cube, I obtained by linear analysis the 
phenomena first described, and by circular analysis those last described, 
beginning at another starting-point. 
4. Phenomena in the different Colours of the Spectrum. 
The foregoing experiments were made in incident homogeneous light, 
the length of whose waves was. In another part of the spectrum, 
however, \ has another value. Let A, represent this: and if 
o—e=mi, o—e=m,X, 
Vor. I—Parr I. G 
