Specific gravity beads

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probably made in Glasgow

Postcard of Specific gravity beads.
© National Museums Scotland

Specific gravity beads

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 wooden box) were made around 1790 by William Twaddell of Glasgow.

The set has 18 glass beads. The inside the lid of the box is stamped 'TWADDELL LATE BROWN IN THE TRONGATE 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.

William Twaddell (fl.1792-1839), a Glaswegian hydrometer and spirit proof maker, learnt his trade with James Brown, continuing Brown's business from 1789 till 1792 for the benefit of Brown's widow.

Record details

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Online ID: 000-100-104-256-C
Image Rights Holder: National Museums Scotland
Project: 0098: National Museums Scotland
Project description | View all records in project
Ref: National Museums Scotland  T.1975.151
Date: Around 1795
c. 1795
What: Bead, gravity / bubble, philosophical
Subject: 22. PHYSICS, Hydrostatics (Departmental Classification)
Who: Twaddell, Glasgow (Maker)
Where: Scotland, Lanarkshire, Glasgow
Description: Set of philosophical beads by Twaddell of Glasgow, c. 1795
  • D.J. Bryden, Scottish Scientific Instrument Makers 1600-1900, Edinburgh, 1972, pp 34-5. 
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