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.' SELF-RECOVERING "COHERER" The study of Electric Waves by Dr. J. C. Bose led not only to the devising of methods for the production of the shortest Electric Waves known but also to the construction of a very delicate 'Receiver' for the detection of invisible other disturbances. The most sensitive form of detector hitherto known was the "Coherer." One of the forms made by Sir Oliver Lodge consisted simply of a glass tube containing iron turnings, in contact with which were wire led into opposite ends of the tube. The arrangement was placed in series with a galvanometer and a battery; when the turnings were struck by electric waves, the resistance between loose metallic contacts was diminished and the deflection of the galvanometer was increased. Thus the deflection of the galvanometer was made to indicate the arrival of electric waves. The arrangement was, no doubt, a sensitive one, but, to get a greater delicacy, Dr. Bose used, instead of iron turnings, spiral springs which were pushed against each other by means of a screw.[10] Still the arrangement laboured under one great disadvantage. The 'receiver' had to be tapped between each experiment. So something better than a 'cohering' receiving was needed--something that was self-recovering, like a human eye. To discover that something, Dr. Bose began a study of the whole theory of 'coherer action.' It was hitherto believed that the electric waves, by impinging on iron and other metallic particles in contact, brought about a sort of fusion--a sort of 'coherence'--and that the diminution of resistance was the