The stroboscope was designed by Joseph of Belgium in 1832, In its simplest form, it is a rotating disc with evenly spaced small openings cut into it. It is placed between the observer and the moving object and rotates to alternately block and reveal the object. When the speed of the disc is adjusted so that it becomes synchronized with the object's movement, the object seems to slow and stop. The illusion is commonly known as the "stroboscopic effect.