George Brown's Rotula Arithmetica
George Brown (1650-1730) is a Scottish arithmetician and minister, known for the invention of an arithmetical instrument, called Rotula Arithmetica—a device for simple addition, subtraction, multiplication and division.
After obtaining of a M.A. degree from Aberdeen's Kings College in 1668, Brown worked as a teacher of mathematics in Edinburgh. Later on, he worked as a minister in Stranraer, schoolmaster in Fordyce, and from 1680 schoolmaster at Kilmaures. In 1690s, he invented Rotula Arithmetica and in 1698 he was given the sole privilege (something like 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 (see a copy of the book), published in 1700 in Edinburgh (see bellow the title page of the book). In the same 1700 he 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.
George Brown's An Account of the Rotula Arithmetica
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.
The brass plate of George Brown's Rotula Arithmetica
The Rotula consists of 2 parts: a circular plain, moving upon a center-pin (movable plate); and a ring, whose circles are described from the same center (fixed plate). The movable plate is inscribed with digits and tables in such manner, that calculations can be done by moving the plate around the axes and accounting the numbers.
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 foresaid and having refused to do the same in time coming...".
Brown is an author of several others mathematical books, popularizing the decimal notation.
George Brown died in 1730 in London.