Hydrostatic bubbles, also known as philosophical bubbles, gravity beads, aerometrical beads and hydrometer beads, are a type of hydrometer invented in 1757 by Alexander Wilson of Glasgow. The design was subsequently improved and patented by the glassblower and instrument maker Isabella Lovi of Edinburgh in 1805. The instrument, which consists of a set of glass beads, seems to have been particular to Scotland and was only used until the early 19th century, when it was largely superseded by more accurate methods.