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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").

Gold coin coin made from gold

A gold coin is a coin that is made mostly or entirely of gold. Most gold coins minted since 1800 are 90–92% gold, while most of today's gold bullion coins are pure gold, such as the Britannia, Canadian Maple Leaf, and American Buffalo. Alloyed gold coins, like the American Gold Eagle and South African Krugerrand, are typically 91.7% gold by weight, with the remainder being silver and copper.

Isaac Newton refers to the coin in a letter to John Locke:

Isaac Newton Influential British physicist and mathematician

Sir Isaac Newton was an English mathematician, physicist, astronomer, theologian, and author who is widely recognised as one of the most influential scientists of all time, and a key figure in the scientific revolution. His book Philosophiæ Naturalis Principia Mathematica, first published in 1687, laid the foundations of classical mechanics. Newton also made seminal contributions to optics, and shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus.

John Locke English philosopher and physician

John Locke was an English philosopher and physician, widely regarded as one of the most influential of Enlightenment thinkers and commonly known as the "Father of Liberalism". Considered one of the first of the British empiricists, following the tradition of Sir Francis Bacon, he is equally important to social contract theory. His work greatly affected the development of epistemology and political philosophy. His writings influenced Voltaire and Jean-Jacques Rousseau, many Scottish Enlightenment thinkers, as well as the American revolutionaries. His contributions to classical republicanism and liberal theory are reflected in the United States Declaration of Independence.

The Jacobus piece coin'd for 20 shillings is the 41th: 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.

Gram Unit of mass 1/1000th of a kilogram

The gram is a metric system unit of mass.

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Shilling Unit of currency formerly used in the United Kingdom, Australia, and other British Commonwealth countries, as well as much of the British Empire

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Troy weight system of units of mass

Troy weight is a system of units of mass that originated in 15th-century England, and is primarily used today in the precious metals industry. Its units are the grain, pennyweight, troy ounce, and troy pound. The grain is the same grain used in the more common avoirdupois system. By contrast, the troy ounce is heavier than the avoirdupois ounce, while the troy pound is lighter than the avoirdupois pound.

Penny (English coin) early coin in the Kingdom of England

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The British Five Guinea coin was a machine-struck currency produced from 1668–1753. It was a gold coin 37 millimetres in diameter and weighing between 41 and 42 grams. Although the coin is now known as the "five guinea" piece, during the 17th and 18th centuries it was also known as a five-pound piece, as during the reign of Charles II a guinea was worth twenty shillings — until its value was fixed at twenty-one shillings by a Royal Proclamation in 1717 the value fluctuated rather in the way that bullion coins do today.

Guinea (coin) coin of approximately one quarter ounce of gold that was minted in Great Britain between 1663 and 1814

The guinea was a coin of approximately one quarter ounce of gold that was minted in Great Britain between 1663 and 1814. The name came from the Guinea region in West Africa, where much of the gold used to make the coins originated. It was the first English machine-struck gold coin, originally worth one pound sterling, equal to twenty shillings, but rises in the price of gold relative to silver caused the value of the guinea to increase, at times to as high as thirty shillings. From 1717 to 1816, its value was officially fixed at twenty-one shillings.

Quarter guinea

The Quarter guinea was a British coin minted only in the years 1718 and 1762. As the name implies, it was valued at one-fourth of a guinea, which at that time was worth twenty-one shillings. The quarter guinea therefore was valued at five shillings and threepence.

The Laurel was the third English gold coin with a value of twenty shillings or one pound produced during the reign of King James I. It was named after the laurel that the king is portrayed as wearing on his head, but it is considerably poorer in both quality and style than the Sovereign and Unite which preceded it. The coin was produced during James I's third coinage (1619-1625), five different busts of the king being used in these years. All the coins were produced at the Tower Mint in London. The laurel weighed 140.5 grains, less than the previous Unite but almost exactly the same as the Unite issued under Charles I.

Florin Gold coin of the Republic of Florence, struck from 1252 to 1533

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Pound sterling Official currency of the United Kingdom and other territories

The pound sterling, commonly known as the pound and less commonly referred to as sterling, is the official currency of the United Kingdom, Jersey, Guernsey, the Isle of Man, South Georgia and the South Sandwich Islands, the British Antarctic Territory, and Tristan da Cunha. It is subdivided into 100 pence. A number of nations that do not use sterling also have currencies called the pound.

Anglo-Saxon pound unit of account in Anglo-Saxon England

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Later life of Isaac Newton

During his residence in London, Isaac Newton had made the acquaintance of John Locke. Locke had taken a very great interest in the new theories of the Principia. He was one of a number of Newton's friends who began to be uneasy and dissatisfied at seeing the most eminent scientific man of his age left to depend upon the meagre remuneration of a college fellowship and a professorship.

Pound Scots unit of currency in the Kingdom of Scotland

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Guernsey pound currency of Guernsey; at par with the pound sterling

The pound is the currency of Guernsey. Since 1921, Guernsey has been in currency union with the United Kingdom and the Guernsey pound is not a separate currency but is a local issue of banknotes and coins denominated in pound sterling, in a similar way to the banknotes issued in Scotland, England and Northern Ireland. It can be exchanged at par with other sterling coinage and notes.

Pistole coin

Pistole is the French name given to a Spanish gold coin in use from 1537; it was a double escudo, the gold unit. The name was also given to the Louis d'Or of Louis XIII of France, and to other European gold coins of about the value of the Spanish coin. One pistole was worth approximately ten livres or three écus, but higher figures are also seen.

From c. 1124 until 1709 the coinage of Scotland was unique, and minted locally. A wide variety of coins, such as the plack, bodle, bawbee, dollar and ryal were produced over that time. For trading purposes coins of Northumbria and various other places had been used before that time; and since 1709 those of the Kingdom of Great Britain, and then of the UK.

Shilling (British coin) British pre-decimalisation coin

The shilling (1/-) was a coin worth one twentieth of a pound sterling, or twelve pence. It was first minted in the reign of Henry VII as the testoon, and became known as the shilling from the Old English scilling, sometime in the mid-sixteenth century, circulating until 1990. The word bob was sometimes used for a monetary value of several shillings, e.g. "ten bob note". Following decimalisation on 15 February 1971 the coin had a value of five new pence. It was made from silver from its introduction in or around 1503 until 1947, and thereafter in cupronickel.

Sovereign (English coin) English gold coin

The English gold sovereign was a gold coin of the Kingdom of England first issued in 1489 under King Henry VII. While the coin typically had a nominal value of one pound sterling, or twenty shillings, the sovereign was primarily an official piece of bullion and had no mark of value on its face. The name derives from the large size and majestic portrait of the monarch, with the obverse of the first sovereigns showing the king full face, sitting on a throne, while the reverse shows the Royal Arms of England and a Tudor double rose.

Crown (English coin) English coin introduced in 1526

The crown, originally known as the "crown of the double rose", was an English coin introduced as part of King Henry VIII's monetary reform of 1526, with a value of five shillings.


  1. A Discourse of Coin and Coinage
  2. Letter of Isaac Newton dated September 19, 1698, to John Locke, concerning the weight and fineness of various coins.