Every three-dimensional artwork interacts with the space around it, because its size, light, and colour affect one’s perception of that space. In the case of Alexander Calder, this interplay goes a critical step further. A breath of air from the viewer sets the object in motion and transforms the invisible breeze into a clearly visible vibration. The same applies to the mobiles – so-called by Marcel Duchamp – constructed by the artist in 1932 as suspended, movable objects made of iron and wire. In this way – seemingly playfully – Calder created an innovative new approach to sculpture in the twentieth century.