"That light is transmitted by waves in the ether is abundantly proved, but the nature of the waves and the nature of the ether have, until the present, always been uncertain. It is known that the ultimate particles of bodies exist in a state of vibration, but it cannot be assumed that the vibration is purely mechanical. Experiment has proved the existence of magnetic and electric strains in the ether, and I have found that electro-magnetic strains are propagated with the same speed as that of which light travels. "You will now realize, to put it in very simple language, that the connection between light and what the man in the street would call currents, or waves of electricity, is very intimate. When I had fully established this in my own mind, I studied the physiology of the human body for a long period. I found that the exciting agents in the nerve system of the animal frame are frequently electric, and by experimenting upon the nerve system in the human eye, I found that it could be excited by the reception of electro-magnetic waves. "In the course of my experiments I began more and more frequently to ask myself, 'What is the exact nature of thought?' "You all know how Signor Marconi can send out waves from one of his transmitters. I am now about to tell you that the human brain is nothing more nor less than an organism, which, in the process of thought, sends out into the surrounding ether a number of subtle vibrations. But, as these vibrations are so akin in their very essence to the nature of light, it occurred to me that it might be possible to gather them together as they were given off, to direct them to a certain point, and then, by means of transforming them into actual light, pass that light through a new form of spectroscope; and, instead of coloured rays being projected upon a screen through the prism of the instrument, the actual living thought of the brain would appear for every one to see. "This is, in brief, precisely what I have done, and it is precisely what I am going to show you in a few minutes. Having given you this briefest and slightest outline of the law I have discovered and proved, I will explain to you something of the mechanical means by which I have proved it, and by which I am going to show it to you in operation." He stopped once more, and moved a little away from where he had been standing. Every one was now thoroughly interested. There was a tremulous silence as the tall, lean figure moved towards a small table on which the shining conical cap, or helmet of brass, lay. Sir William took up the object and held it in his right hand, so that every one could see it distinctly. From the top, where the button of an ordinary cap would be, a thin silk-covered wire drooped down to the floor and finally rose again and disappeared within a complicated piece of mechanism a few feet away.