opaque to Light (e.g. pitch, coal-tar etc.) are transparent to Electric Waves. He next determined the Index of Refraction of various substances for invisible Electric Radiation and thereby eliminated a great difficulty which had presented itself in Maxwell's theory as to the relation between the index of refraction of light and the di-electric constant of insulators. He then determined the wave length of Electric Radiation as produced by various oscillators.

HIS EARLY CONTRIBUTIONS AND THEIR APPRECIATIONS

His first contribution was 'On Polarisation of Electric Rays by Double Refracting Crystals.' It was read at a meeting of the Asiatic Society of Bengal, held on the 1st May 1895, and was published in the Journal of the Society in Vol. LXIV, Part II, page 291. His next contributions were 'On a new Electro polariscope' and 'On the Double Refraction of the Electric Ray by a Strained Di-electric.' They appeared, in the Electrician, the leading journal on Electricity, published in London. These 'strikingly original researches' won the attention of the scientific world. Lord Kelvin, the greatest physicist of the age, declared himself 'literally filled with wonder and admiration for so much success in the novel and difficult problem which he had attacked.' Lord Rayleigh communicated the results of his remarkable researches to the Royal Society. And the Royal Society showed its appreciation of the high scientific value of his investigation, not only, by the publication, with high tributes, of a paper of his 'On the Determination of the Indices of Electric Refraction,' in December 1896, and another paper on the 'Determination of the Wave-length of Electric Radiation,' in June 1896, but also, by the offer, of their own accord, of an appropriation from the Special Parliamentary Grant made to the Society for the Advancement of Knowledge, for continuation of his work.

In recognition of the importance of the contribution made by Prof. Bose, the University of London conferred on him the Degree of Doctor of Science and the Cambridge University, the degree of M.A., in 1896. And, to crown all, the Royal Institution of Great Britain—rendered famous by the labour of Davy and Faraday, of Rayleigh and Dewar—honoured him by inviting to deliver a 'Friday Evening Discourse' on his original work. It would not be out of place to observe that the rare privilege of being invited to deliver a 'Friday Evening Discourse' is regarded as one of the highest distinction that can be conferred on a scientific man.

HIS FIRST SCIENTIFIC DEPUTATION. (1896-97)

The Government of India showed its appreciation of his work by deputing him to Europe to place the results of his investigations before the learned Scientific Bodies. He remained on his Deputation from the 22nd July 1896 to the 19th April 1897. He read a paper 'On a complete Apparatus for studying the Properties of Electric Waves' at the meeting of British Association, held at Liverpool, in 1896. He then communicated a paper 'On the Selective Conductivity exhibited by Polarising Substances,' which was published by the Royal Society, in January 1897. He next delivered his 'Friday Evening Discourse,' at the Royal Institution, 'On Electric Waves,' on the 29th January 1897. "There is, however, to our thinking" wrote the Spectator at the time "something of rare interest in the spectacle presented of a Bengalee of the purest descent possible, lecturing in London to an audience of appreciative European savants upon one of the most recondite branches of the modern physical science." He was then invited to address the Scientific Societies in Paris. "Prof. J. C. Bose" wrote the Review Encyclopedique, Paris "exhibited on the 9th of March before the Sorbonne, an apparatus of his invention for demonstrating the laws of reflection, refraction, and polarisation of electric waves. He repeated his experiments on the 22nd, before a large number of members of the Academie des Sciences, among whom were Poincare, Cornu, Mascart, Lipmann, Cailletet, Becquerel and others. These savants highly applauded the investigations of the Indian Professor." M. Cornu, President of the Academy of Science, was pleased to address Professor Bose as follows:—

"By your discoveries you have greatly furthered the cause of Science. You must try to revive the grand traditions of your race which bore aloft the torch light of art and science and was the leader of civilization two thousand years ago. We, in France applaud you." This fervent appeal, we shall see, as we proceed, did not go in vain.

He was next invited to lecture before the Universities in Germany. At Berlin, before the leading physicists of Germany, he gave an address on Electric Radiation, which was subsequently published in the Physikaliscen Gesellschaft Berlin, in April 1897.

FURTHER RESEARCHES ON ELECTRIC WAVES

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