The earliest precursors to movies were magic lantern shows. Magic lanterns used a glass lens, a shutter and a powerful lamp to project images from glass slides onto a white wall or screen. These slides were originally hand-painted. The invention of the Argand lamp in the 1790s, limelight in the 1820s and the intensely bright electric arc lamp in the 1860s increased the brightness of the images. The magic lantern could project rudimentary moving images, which was achieved by the use of various types of mechanical slides. Typically, two glass slides, one with the stationary part of the picture and the other with the part that was to move, would be placed one on top of the other and projected together, then the moving slide would be hand-operated, either directly or by means of a lever or other mechanism. Chromotrope slides, which produced eye-dazzling displays of continuously cycling abstract geometrical patterns and colors, were operated by means of a small crank and pulley wheel that rotated a glass disc. Still photographs were used later on after the widespread availability of photography technologies after the mid-19th century. Magic lantern shows were often given at fairs or as part of magic shows. A magic lantern show at the 1851 World's Fair caused a sensation among the audience.