Specific gravity beads

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Specific gravity beads are used to measure the density of a liquid at a given temperature and thus its alcohol content. These beads (pictured here in their circular case) were made around 1780 by James Brown of Glasgow. They were made to a design by Alexander Wilson of Glasgow.

The set originally contained 18 beads, but two are now missing. The printed label inside the lid of the box includes the words 'Invented/by the maker/James Brown/ GLASGOW'. The beads were of different buoyancy, and were successively dropped into a liquid in sequence until just one sank, providing the measurement as marked.

James Brown was a Glaswegian spirit-proof maker, in business from 1773, until his death in 1789, when the business was continued on his widow's behalf by William Twaddell, Brown's former apprentice. Brown made and sold the glass calibrated specific gravity beads for testing spirituous liquors invented by Alexander Wilson (1714-86), professor of astronomy at the University of Glasgow from 1760.

Record details

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• Online ID: 000-100-104-221-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland
  Project description   View all records in project
• Ref: National Museums Scotland  T.1938.147
• Date: Around 1780
  c. 1780
  
• Material: Inscription: Invented by the maker James Brown, Glasgow [in lid]
  Bead, gravity / bubble, philosophical / box
  
• Dimensions: 2.88" D (box)
  
• What: Bead, gravity / bubble, philosophical / box
  
• Subject: 22. PHYSICS, Hydrostatics (Departmental Classification)
  
• Who: James Brown, Glasgow (Gravity bead maker and inventor)
  
• Where: Scotland, Lanarkshire, Glasgow
  
• Event:
• Description: Set of eighteen specific gravity beads, two missing, in a circular box, for proving spirits, etc, with "Invented by the maker James Brown, Glasgow" inscribed in the lid, c. 1780
  
• References:
  • Article 'Hydrodynamics' in the Edinburgh Encyclopaedia vol. 11, Edinburgh, 1817, p. 441D.J. Bryden, Scottish Scientific Instrument Makers, 1600-1900, Edinburgh, 1972, pp. 34-5 
  • Glasgow Journal, 9 September 1773. 
  • P. Wilson, 'Biographical account of Alexander Wilson, AM., Professor of Practical Astronomy in the University of Glasgow', Transactions of the Royal Society of Edinburgh 10 (1826), pp.287-8. 
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