Epsom, ep'sum, a small market town in Surrey, fifteen miles southwest of London. It has given its name to the famous Epsom salts, formerly manufactured there from the water of mineral springs found in the locality. This water is impregnated with sulphate of magnesium similar to that of Seidlitz waters. When evaporated the mineral substances crystallize in snow white rectangular prisms, or in flakes and granules. Epsom salts is a well known household remedy of disagreeable taste. A mile and a half south of the town is a plain called Epsom Downs, where horse races have been held since the day of Charles I. The famous Derby Day races are held here. See DERBY.