Having received the most generous and wide appreciation of his work, Dr.
J. C. Bose continued, with redoubled vigour, his valuable researches on
Electric Waves. He studied the influence of thickness of air-space on
total reflection of Electric Radiation and showed that the critical
thickness of air-space is determined by the refracting power of the
prism and by the wave-length of the electric oscillations. He next
demonstrated the rotation of the plane of polarisation of Electric Waves
by means of pieces of twisted jute rope. He showed that, if the pieces
are arranged so that their twists are all in one direction and placed in
the path of radiation, they rotate the plane of polarisation in a
direction depending upon the direction of twists; but, if they are mixed
so that there are as many twisted in one direction as the other, there
is no rotation.[9] He communicated to the Royal Society the results of
his new researches. And the Royal Society published, in November 1897,
his papers 'On the Determination of the Index of Refraction of glass for
the Electric Ray' and 'On the influence of Thickness of Air-space on
Total Reflection of Electric Radiation' and, in March 1898, his further
contributions 'On the Rotation of Plane of Polarisation of Electric
Waves by a twisted structure' and 'On the Production of a "Dark cross"
in the Field of Electro-magnetic Radiation.'