Dr. Bose, in course of his lecture, spoke of the imperfection of our senses. Our ear, for example, fails to respond to all sounds. There are many sounds to which we are deaf. This was because our ear was tuned to answer to the narrow range of eleven octaves of sound vibrations. He showed a remarkable experiment of an artificial ear which remained irresponsive to various sounds, but when a particular note, to which it was tuned, was sounded even at the distant end of the hall, this ear picked it up and responded violently. As there were sounds audible and inaudible, so there were lights visible and invisible. The imperfection of our eye as a detector of ether vibrations was, however, far more serious. The eye could detect ether vibrations lying within a single octave--between 400 to 800 billion vibrations per second. Comparatively slow vibrations of ether did not affect our eye and the disturbances they give rise to well-known as electric waves. The electric waves, predicted by Maxwell, were discovered by Hertz. These waves were about three metres long. They were about ten million times larger than the beams of visible light. Dr. Bose showed that the three short electric waves have the same property as a beam of light, exhibiting reflections, refraction, even total reflection, through a black crystal, double refraction, polarisation, and rotation of the plane of polarisation. The thinnest film of air was sufficient to produce total reflection of visible light with its extremely short wave lengths. But with the new electric waves which he produced, Dr. Bose showed that the critical thickness of air space determined by the refracting power of the prison and by the wave length of electric oscillations. Dr. Bose determined the index of refraction of electric waves for different materials, and eliminated a difficulty which 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 also measured the wave lengths of various oscillations. The order to produce short electric oscillations, to detect them and study their optical properties, he had to construct a large number of instruments. It was a hard task to produce very short electric waves which had enough energy to be detected, but Dr. Bose overcame this difficulty by constructing radiators or oscillators of his own type, which emitted the shortest waves with sufficient energy. As a receiver he used a sensitive metallic coherer, which in itself led to new and important discoveries. When electric waves fall on a loose contact between two pieces of metals, the resistance of the contact changes and a current passes through the contact indicating the existence of electrical oscillations. Dr. Bose discovered the surprising fact that with potassium metal the resistance of the contact increases under the action of electric waves and that this contact exhibits an automatic recovery.