A Jacobus is an English gold coin of the reign of James I, worth 25 shillings ( pound sterling). The name of the coin comes from the Latin inscription surrounding the King's head on the obverse of the coin, <small>IACOBUS D G MAG BRIT FRA ET HI REX</small> ("James, by the grace of God, of Britain, France, and Ireland King").
Isaac Newton refers to the coin in a letter to John Locke:
These correspond to masses of 9.10 and 9.82 grams respectively, making the broad Jacobus slightly heavier.