The characteristics of the third modification of ether are such that they prompted Rudolf Steiner to give it as a second name, besides chemical ether, that of sound-ether. In view of the fact, stressed at the beginning of this chapter, that perception of the ether is achieved by a heightening of the power of the spirit-eye, it must cause surprise to learn that a certain mode of activity of the ether has a quality which makes appeal to aural experiences. The full answer to this riddle must await the discussion that follows this chapter. Two points, however, may be brought forward at once. Firstly, where gravity, with its tendency to individualize, is absent, no such sharp distinctions exist between one form of perception and another as are found in the sphere of the physical senses.6 Secondly, even in ordinary sense-perception a certain overlapping of visual and aural experiences is known to us. We need only think how common it is to give musical attributes, such as 'consonant' and 'dissonant' to colours, and to describe tones as 'light' and 'dark'. The reason is that subconsciously we accompany visual experiences with tone-sensations, and vice versa. Cases are even known of human beings in whom the secondary sensation occurs with such intensity as to equal the primary one. Such people say that they 'see' sounds and 'hear' colours. * Everything that is true of the supersensible sphere we may expect to come to expression in some form in the world of sense-perception. The sphere of the ether is the sphere of the creative archetypes of the world, and when we learn that to one part of this world the character of sound is attributed, we must search for a phenomenon, perceptible to our senses, which reveals to us the secret of the sound's form-creating power. This we have in the so-called sound-figures, discovered by the German physicist Chladni (1756-1827) and called after him 'Chladni's sound-figures'. A short description of how they are produced will not be out of place. A round or square plate of glass or brass, fixed at its centre so that it can vibrate freely at its edges, is required. It is evenly and not too thickly covered with fine sand or lycopodium powder and then caused to vibrate acoustically by the repeated drawing of a violin-bow with some pressure across the edge of the plate until a steady note becomes audible. Through the vibrations thus caused within the plate, the particles of sand or powder are set in movement and caused to collect in certain stationary parts of the plate, thereby creating figures of very regular and often surprising form. By stroking the plate at different points on the edge, and at the same time damping the vibrations by touching the edge at other points with the finger, notes of different pitch can be produced, and for each of these notes a characteristic figure will appear (Fig. 14).7