Polarization of rainbows

The theory of rainbows is well known and features in a number of textbooks on optics as well as general physics. One striking feature which is rarely mentioned in such accounts but is often noticed by observant students is that the light from rainbows is strongly plane polarized (Preston 1895). The phenomenon can be observed easily by viewing through polarizing sunglasses. The plane of polarization (plane of the electric vector) is tangential to the arc so that when viewed normally the top section of the bow appears missing; by rocking the head the missing sector moves round the arc. An account of this phenomena is given.