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01 Two Scales for Weighing Gold Coins

image of Two Scales for Weighing Gold Coins

These two (almost identical) money scales emphasise both the skill of the inventors, and the ingenuity utilised in combating the extensive counterfeiting of gold coins prevalent some 250 years ago. Both models are exceedingly rare.

These balances are of the 'shelf-edge' type, manufactured by Bradford, Darby & Hulls in Chipping Camden, Gloucestershire, England and patented in 1753. The scales work as a steelyard but, instead of being suspended, they are placed on the edge of a shelf or table. The sharp pointed feet underneath the beam are the pivots. The unsigned earlier version c.1753 is behind and the alternative version for hydrostatic weighing c.1770 is in front. The latter’s sliding weight is marked ‘BY THE KINGS PATENT BRADFORD DARBY & HULLS’. The swan-neck fitting can be moved out to an alternative position for hydrostatical weighing, for which a second line of graduations is provided. They were used to weigh coins circulating in Britain during that period (Guinea, Portugal Piece, and Moidore), with their sub-divisions ranging from 4 shillings and 6 pence, to £3 pounds 12 shillings.

The coin to be authenticated is placed in the pincers and dangled over the edge of the shelf. The weight is moved to the position indicated on the beam as the correct weight for that particular coin. If necessary, the weight is adjusted to achieve a balance - e.g.,ifthecoin is worn, etc. The whole divisions are equal to one shilling each. The graduations A & B are for weighing in air. Those marked W are for weighing in water. If the coin is made from gold, it will weigh correctly in both air and water. If it was counterfeit but of the right weight (made, say, of gilded lead), it would weigh incorrectly in water.

Private Collection, London.

The 1753 Patent of William Bradford and Jonathan Hulls also includes a description of a slide rule for use in general calculations and, perhaps for the first time in 250 years, all three instruments are here united; the slide rule coming from the Museum’s collection (inv. 44586). It is numbered 9 on the display stand behind the scales. As the slider had a reversed line, it was being recommended in a magazine in 1841 and the readers were encouraged to find a second-hand example.

Each balance is contained in a tooled, black leather case stamped ‘RD’, this could be either the initials of the case maker or the instrument maker. The original patent was only granted to William Bradford, Schoolmaster, and Jonathan Hulls, Yeoman – without a mention of Darby. However, R. Darby was included in the list of authors in a description of the coin scales and slide rule published in 1761.


See: British Patent Specification No. 686 of 1753.
W.Bradford, R.Darby, J.Hulls, Abstract of his Majesty’s Royal Letters Patent. A portable Instrument for detecting Frauds by Counterfeit Gold bound with The Art of Measuring Made Easy by the Help of a New Sliding Rule, Stratford 1761.
Mechanics Magazine, Vol.XXXIV 1841, p. 111.

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