A Jacobus is an English gold coin of the reign of James I, worth 25 shillings (

pound sterling Sterling (symbol: £; currency code: GBP) is the currency of the United Kingdom and nine of its associated territories. The pound is the main unit of sterling, and the word '' pound'' is also used to refer to the British currency general ...

). The name of the coin comes from the Latin inscription surrounding the King's head on the obverse of the coin, IACOBUS D G MAG BRIT FRA ET HI REX ("James, by the grace of God, of Britain, France, and Ireland King").

Isaac Newton Sir Isaac Newton () was an English polymath active as a mathematician, physicist, astronomer, alchemist, theologian, and author. Newton was a key figure in the Scientific Revolution and the Age of Enlightenment, Enlightenment that followed ...

refers to the coin in a letter to

John Locke John Locke (; 29 August 1632 (Old Style and New Style dates, O.S.) – 28 October 1704 (Old Style and New Style dates, O.S.)) was an English philosopher and physician, widely regarded as one of the most influential of the Enlightenment thi ...

'' The Jacobus piece coin'd for 20 shillings is the : part of a pound Troy, and a Carolus 20s piece is of the same weight. But a broad Jacobus (as I find by weighing some of them) is the 38th part of a pound Troy.''Letter of Isaac Newton
dated September 19, 1698, to
John Locke John Locke (; 29 August 1632 (Old Style and New Style dates, O.S.) – 28 October 1704 (Old Style and New Style dates, O.S.)) was an English philosopher and physician, widely regarded as one of the most influential of the Enlightenment thi ...
, concerning the weight and fineness of various coins.

These correspond to masses of 9.10 and 9.82 grams respectively, making the broad Jacobus slightly heavier.

References

Coins of England English gold coins {{coin-stub