Jacobus

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

[1] 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 refers to the coin in a letter to John Locke: The Jacobus piece coin'd for 20 shillings is the 41st: 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.

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