"Galvani happened to hang some skinned frogs on an iron railing, with the intention of making them into soup, and, as chance would have it, tried the experiment of connecting the spinal column with the nerve of their legs by means of a bent wire made of tin and copper. Then he noticed that the legs twitched violently every time he made the connection, although they had been dead for some hours. He had no sooner published the account of what had happened than he became the laughing stock of Bologna; and no one thought sufficient of the experiment to repeat it for himself, and yet Galvani had discovered electricity, the greatest and most universally employed force that we know of. And if I tell you of this new force which I hope to exhibit to you some day, perhaps you will go away laughing at me, and saying, 'We don't understand what you are saying, and therefore you are talking nonsense.' If I 'will' to take this weight and raise it with my arm above my head, my will moves matter and overcomes gravity. What is the force which enables me to do it? You do not know. Neither do I, and yet no one in this room doubts that I have done it, because everyone of us performs a similar act a thousand times a day. "Physiologists will tell you that every object we see forms a little image on a nervous layer at the back of our eyes, but they cannot tell you how that image is perceived by the mind, nor can they explain why the image appears so large--in fact life size--since the image on the retina (at the back of the eye) is a mere speck compared with the size of the image as it appears to us.