To help the child develop a special facet of the thermic sense, which allows one, by touch alone, to distinguish between materials with different capacities to conduct heat. Dense minerals such as stone, steel or copper, conduct heat very well and feel cool to the touch, since they draw heat off our skin rather than reflect it back. Porous, organic materials, such as rubber, wood or felt, conduct heat poorly and feel warm to the touch, since they reflect body heat back against our skin, rather than draw it off. Surfaces that feel cool to the touch are generally percieved to be different in composition from surfaces that feel warm.