The kaleidoscope 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. Setting of the mirrors at 45 degrees creates eight duplicate images, at 60 degrees six, and a 90 degrees four. As the tube is rotated the tumbling of the coloured beads causes colour and pattern changes seen by the viewer.
Invented by Sir David Brewster in 1816 while conducting experiments on light polarity. 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.