A powerful cognitive illusion that causes approximately 98 per cent of people to judge an object to be heavier than another object of the same weight but much larger size when the two are lifted by hand. In a simple home demonstration of the illusion, pieces of lead or other heavy material may be placed in two different-sized containers and surrounded by sand to prevent them from moving about and from being visible if the containers are transparent, and the weights of the containers may be adjusted until they are identical, whereupon the smaller container will feel much heavier than the larger one. In a classic experiment on this illusion, 100 US military officers judged a smaller object to be on average two and a half times as heavy as one that was the same weight but twice the size in each dimension. The illusion was first reported in 1889 by the German psychologists Georg Elias Müller (1850–1934) and Friedrich Schumann (1863–1940). It is sometimes classified as a tactile illusion. Also called Charpentier's illusion.