“Can you see this opening?” We all replied that we could not, and crowded around him. As we drew close to it a small hole about the diameter of a lead pencil became visible by concentration on the spot touched by the knife. Unless we had been deliberately searching for it, it is probable that it would have gone entirely unnoticed, due to its location on one of the dark spots in the pattern of the paper itself. “This,” said the doctor, “is one of Hegel’s eyes.” He lightly tapped inside the hole with the point of his knife and we heard it click against some hard substance. Then he cut a square of paper and plastering from around it, disclosing a black box which bore a close resemblance to a small camera with a tiny lens in front. Taking a small screwdriver from his pocket, he removed the front of the box, the back of which was covered with row on row of small, circular affairs which he described as photoelectric cells. “Each cell,” he said, “responds, according to the strength of light or shade which strikes it through the lens, with a different wave length. These various wave lengths are combined and transmitted from a common antenna. At the receiving station, the process is reversed, and this image is built up on ground glass by various vibrating light beams. For a thorough description of this process, which I will not go into here, I refer you to the book, ‘Radio for All.’ There are four ‘eyes’ like this one in this room alone. Every other room in this house is as thoroughly equipped. “And now for the ears.” He examined the wall until he found another hole, into which he thrust the knife blade. Then he removed another square of wall paper and plaster, revealing one of those instruments with which we were all familiar--the microphone. “As this instrument needs no explanation,” he said, “I will now show you how our friend Hegel managed to lock, unlock, open and close doors from a distance of eight miles.” He walked to the door and opened it. “This door,” he said, “shows no signs of having been tampered with in any way, yet I am convinced that there are at least two electric wires connecting it with the current which Hegel tapped somewhere in front of the meter--I have not yet discovered where.”