The magic wand: a new stereokinetic anomalous surface.

When a disc with two dots stuck on it a few centimetres apart is set in slow rotatory motion, the two dots appear displaced in depth and rigidly connected to form the two extremities of a rod. The rod appears as a diaphanous transparent object, slightly tinted to the same colour as the dots. Experimental analysis of the phenomenon shows that it is different from previously observed 'moving phantoms', 'motion-induced contours', and 'stereokinetic induced phantoms'. But it shows similarities with all three phenomena: the colour spreading along the apparent rod is facilitated by low illumination and is clearly visible under high illumination with bright colours only; it is seen only when the two dots appear to move with apparent displacement in depth and not when they appear to lie on the plane of the disc. When line-drawn circles instead of full colour dots are used, the anomalous surface of the rod appears to have colourless vitreous transparency. With half-line circles it is clearly visible as an opaque rod of the same colour as the background. When squares or diamonds are used instead of dots, a three-dimensional prism can be observed which has similar appearance to the rod.