is a tube of mirrors with some loose coloured beads. The viewer looks in one end and light
enters the other end reflecting
off the mirrors. Typically there are two rectangular lengthways mirrors. Setting of the mirrors at 45 degrees creates eight duplicate images, at 60 degrees six, and at 90 degrees four. As the tube is rotated the tumbling of the coloured beads causes colour and pattern changes seen by the viewer. Any arbitrary pattern of beads shows up as a beautiful symmetric pattern.
Invented by Sir David Brewster in 1816 while conducting experiments on light polarization, it was patented in 1817. The initial design was made from a tube in which Brewster placed pairs of mirrors at one end, and pairs of translucent disks at the other end. Between the two, he placed the beads. Initially intended as a science tool it was quickly copied as a toy.