This small, blown-glass hydrostatic balance consists of an arm suspended on a fulcrum at its center. A small sealed glass sphere hangs from one end of the arm; a small basket containing crystal fragments hangs at the other end. The balance measures the density of fluids. This is done by immersing the glass sphere in a fluid. To counterbalance the buoyancy of the fluid and keep the balance in equilibrium, it is necessary to place a weight (corresponding to a certain number of crystal fragments) in the basket. The denser the fluid, the fewer the crystal fragments needed to achieve equilibrium. The instrument combines the principles of Archimedean upward thrust and of Galileo's bilancetta [small balance].