sky on a sunny day. You will find that the angle of polarization and
the intensity of the polarized light passing through the lens changes
depending upon where in the sky you look. The human visual system,
without the aid of a polarizing filter, is not sensitive to this property
of sunlight. However, many insects, birds, reptiles, and other animals
are. This discovery was originally made by Karl von Frisch in his ex-
periments with honeybees. Again, from his Nobel Prize lecture:
0°FiZ2 2S
Md (0S Ss ves &
/\ VAN Wwe“, es 1 yt ON
90°|, Py VANS VSNL SOY “y fa TE | 490°
Vy ~~ we 4 |\ NX ~ _—_——_— o 4
~ ay180°
Figure 11.6. The angle and intensity of skylight polarization, indicated by the
direction and thickness, respectively, of the short bars. The intensity of polar-
ization is greatest 90 degrees from the position of the sun.I noticed that a view of the blue sky is the same as a view of the sun.
When clouds passed over the section of the sky visible to the bees, disori-
ented dances immediately resulted. Therefore they must have been able
to read the sun’s position from the blue sky. The direction of vibration
of polarized blue light differs in relation to the sun’s position across the
entire vault of the sky. Thus, to one that is able to perceive the direction