Our everyday experience is full of another series of activities even more mysterious than these movements of the iron. Whenever we open our eyes we see objects and colors confronting us and located in spaces far and near. What brings the object to us? What operates to produce the contact? How does the far-away thing hit our organ of vision? This was to the ancient philosopher a most difficult problem, a real mystery. He made many guesses at a solution, but no guess which he could make satisfied his judgment. Our answer is that an invisible and intangible substance which we call ether—luminiferous ether—fills all space, even the space occupied by visible objects, and that this ether which is capable of amazing vibrations, billions of them a second, is set vibrating at different velocities by different objects. These vibrations bombard the minute rods and cones of the retina at the back of the eye and, presto, we see now one color and now another, now one object and now another. This ether would forever have remained unknown to us had not this marvelous structure of the retina given it a chance to break through and reveal itself. In many other ways, too, this ether breaks through into revelation. It is responsible apparently for all the immensely varied phenomena of electricity, probably, too, of cohesion and gravitation. Here, again, the revelations remained inadequate and without clear interpretation until we succeeded in constructing proper instruments and devices for it to break through into active operation. The dynamo and the other electrical mechanisms which we have invented do not make or create electricity. They merely let it come through, showing itself now as light, now as heat, now again as motive power. But always it was there before, unnoted, merely potential, and yet a vast surrounding ocean of energy there behind, ready to break into active operation when the medium was at hand for it.