crystalline lens in fishes and quadrupeds . 
3*3 
5, 6 , 11, 12, are extremely faint, and are seen with consi- 
derable difficulty in this position of the lens. 
If the crystalline is now turned round, so that its axis, 
which corresponds to the axis of vision, may always be parallel 
to the polarised ray, the same appearances will be seen with- 
out the slightest variation . But if this axis is inclined to the 
polarised ray in the direction 1,2, the sectors 1, 2, will dimi- 
nish, and 7, 8, will increase in size, and an additional white 
spot will appear at the centre as in Fig. 2, till by increasing 
the inclination, the sectors 1, 2, and the white spot will com- 
pletely disappear, leaving the sectors 7, 8, much enlarged and 
of a bluish white tint. If the inclination is in the direction 7, 8, 
the sectors 1, 2, will increase, and 7, 8, will diminish in the 
flliSiD y *cJnyin! A'? yrJt *11. Ill 
same manner. 
By transmitting the polarised light through other two faces 
of the glass paralielopiped, so as to traverse the crystalline in 
a line perpendicular to its axis, the optical figure presented 
new appearances. When the axis of the lens was either 
parallel or perpendicular to the plane of primitive polarisation, 
which happened four times in the course of a revolution, it 
exhibited the form shown in Fig. 3. The tints 1 , 2, 7, 8, were 
now reduced to a pale blue of the first order, and the black 
cross was very ill defined at the centre. The middle sectors 
3, 4, 9, 10, were a little reduced in size, while the exterior 
ones 5, 6, 11, 12, had experienced a very sensible augmen- 
tation. At intermediate positions of the crystalline, when its 
axis was inclined 45 0 , *35°, 225 0 , and 315 0 to the plane of 
primitive polarisation, the optical figure assumed the appear- 
ance shown in Fig. 4, where the two sectors 7, 8, are greatly 
enlarged, and the other two 1, 2, have wholly, or almost 
wholly, disappeared. 
