George Brown

I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.
Galileo Galilei

George Brown's An Account of the Rotula Arithmetica
George Brown’s An Account of the Rotula Arithmetica

George Brown (1650-1730) is a Scottish arithmetician and dissenting minister, known primarily for the invention of an arithmetical instrument, called Rotula Arithmetica—a very simple and not very successful calculating device for addition, subtraction, multiplication, and division.

It seems Brown invented Rotula Arithmetica sometime in the 1690s, as in 1698 he was given the sole privilege (something like a patent) to frame, make and sell his instrument for the space of 14 years…

Brown described his instrument in the book An Account of the Rotula Arithmetica, published in 1700 in Edinburgh (see below the title page of the book). In the book, he described also his new method of teaching the simple rules of arithmetic. In the same year, 1700 Brown published also another book, called A Specie Book, to be used in conjunction with the Rotula Arithmetica. The book contains currency tables because many of the coins were not Scots-minted silver, but foreign currency, legal tender in Scotland, at values fixed by the Privy Council and Parliament.

Several copies of the instrument were made, but it is doubtful that Brown himself made the rotula, he probably employed an engraver. The instrument in the lower photo is inscribed for the right Honble Patrick Earle of Marchmont, Lord High Chancelour of Scotland, Feb 28. 1699, as Brown was clearly searching for an influential patron (Sir Patrick Hume (1641-1724) was a Scottish statesman).

The brass plate of George Brown's Rotula Arithmetica
The brass plate of George Brown’s Rotula Arithmetica (© National Museums Scotland)

Rotula Arithmetica consists of two parts: a circular plain (movable plate), moving upon a center-pin; and a ring (fixed plate), whose circles are described from the same center. The outermost circular band of the movable, and the innermost of the fixed, are divided into a hundred equal parts, and these parts are numbered 0, 1, 2, 3. etc. Upon the ring, there is a small circle having its circumference divided into ten equal parts, furnished with a needle that shifts one part at every revolution of the movable. With this simple instrument, the calculations can be done by moving the plate around the axes and accounting the numbers, as the four arithmetical operations can be performed not only for integers but also for decimals finite and infinite.

Biography of George Brown

Not a whole lot is known about George Brown. Born in 1650, Brown attended Aberdeen’s Kings College, matriculating in 1664 and graduating in 1668. Then he worked as a teacher of mathematics in Edinburgh. Later on, he worked as a minister in Stranraer, schoolmaster of Fordyce School, Banffshire, and from 1680 schoolmaster in Kilmaures, Ayrshire.

Arithmetica Infinita; or The Accurate Accomptant's Best Companion contriv'd and calculated by the Reverend George Brown
Arithmetica Infinita; or The Accurate Accomptant’s Best Companion contriv’d and calculated by the Reverend George Brown. The author’s engraved portrait is on the page opposite the title page (© National Museums Scotland)

George Brown was a good mathematician, but a poor minister. He wasn’t zealous in prayers and was frequently charged for exercising discipline and marrying without proclamation. He was banished from Edinburgh from 1692 until 1698, for “… he had not prayed for their said majesties and in the terms aforesaid and having refused to do the same in time coming…”.

Brown is the author of several other mathematical books, popularizing the decimal notation, considered to be important works at the time. The last of them, Arithmetica Infinita; or The Accurate Accomptant’s Best Companion contriv’d and calculated by the Reverend George Brown, published in 1717-1718 in London, was endorsed by the famous Scottish mathematician John Keill.

George Brown died in 1730 in London.