For ropes in the grooves of cast-iron pulleys, where 4, is the inclination of the sides of the grooves, the value of the normal pressure is increased in the ratio of **cosec** zct) = I.

A usual value of for hemp ropes on cast-iron pulleys is 0.3, and the exponential log ratio is therefore 0 3ur **cosec** 20 when 9 =7r.

Applying this interpretation to the formulae given above, it follows that when the incident light is polarized at an azimuth a to the plane of incidence and the second medium is the less refracting, the reflected light at angles of incidence exceeding the critical angle is elliptically polarized with a difference of phase A between the components polarized in the principal azimuths that is given by tan (A/2) =cot i l l (1 - µ 2 **cosec** 2 i).