Hydrostatic bubbles, also known as philosophical bubbles, gravity beads, aerometrical beads and hydrometer beads, are a type of

hydrometer A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically Calibration, calibrated and Graduation (instrument), graduated with one or more scales suc ...

invented in 1757 by Alexander Wilson of

Glasgow Glasgow is the Cities of Scotland, most populous city in Scotland, located on the banks of the River Clyde in Strathclyde, west central Scotland. It is the List of cities in the United Kingdom, third-most-populous city in the United Kingdom ...

. The design was subsequently improved and patented by the glassblower and instrument maker Isabella Lovi of

Edinburgh Edinburgh is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. The city is located in southeast Scotland and is bounded to the north by the Firth of Forth and to the south by the Pentland Hills. Edinburgh ...

in 1805. The instrument, which consists of a set of glass beads, seems to have been particular to Scotland and was only used (for example, in determining the density of spirits) until the early 19th century, when it was largely superseded by more accurate methods.

Operating principle

In Lovi's version of the instrument, a set of hollow glass beads was created, each differing in density from the next by 0.002 units. When added to a liquid of unknown density, the beads that were more dense than the liquid sank, and those that were less dense than the liquid floated. The density of the liquid was indicated as falling between the density of the least dense bead that sank, and the most dense bead that floated.Irving, H. “The Applications of Floating Equilibrium to the Determination of Density.” Science Progress (1933- ), vol. 31, no. 124, 1937, pp. 654–65. JSTOR, http://www.jstor.org/stable/43411915. Accessed 30 Aug. 2022. The operating principle is similar to that of the Galilean thermometer.

References

{{reflist Laboratory equipment Laboratory glassware Density meters Scottish inventions 18th-century inventions