diamagnetism is a type of magnetism. they very weakly repel magnets. most substances are diamagnetic. it was discovered in 1778 when someone saw that bismuth and antimony repelled a magnet. diamagnetic things can be levitated. a frog was levitated in a very strong magnet. water can be repelled by a magnet because it is diamagnetic. it is too weak to be noticed normally, though.