**Richard Delamain** was an English mathematician who invented a circular slide rule.

- It is commonly stated that he studied mathematics at Gresham College, London, but the only evidence for this is a scornful comment by William Oughtred when he is attacking Delamain's lack of expertise.
- This is, we believe, reading too much into a comment by Oughtred which was meant to be hurtful to Delamain.
- Now we have come to the crux of the problem in giving any details of Delamain's education.
- Our only information on this comes from Oughtred when he is trying his hardest to talk down Delamain's abilities.
- We therefore have to tread carefully and try to produce a balanced view of Delamain despite the deliberately unbalanced view presented by Oughtred.
- It would appear that Delamain was not familiar with languages other than English, and his education had not given him Latin or French.
- Delamain took the degree of a Justices Clerk, or a Doctor of Physic, or both.
- Certainly, Delamain became a student of Oughtred's and they were great friends at first.
- Certainly Oughtred claims to have taught Delamain astronomy, conic sections and optics.
- Delamain also claimed to have been tutored by Edmund Gunter.
- Their eldest son, also named Richard, was baptized on 7 March 1627 at St Andrew's Church, Holborn, and became a clergyman, although he certainly had some mathematical skills which he put to good use.
- Delamain was the same age as the king, both being born in 1600.
- Delamain described a circular slide rule in a 32 page pamphlet Grammelogia; or the mathematical ring which he sent as a gift to the King in 1629.
- The King was impressed and he made a grant to Delamain to cover the cost of printing the Grammelogia and making his mathematical-ring.
- The pamphlet was published in January of the following year and Delamain's fame as a mathematician rests on this work.
- Then on 20 May 1633 the King appointed Delamain as an engineer in the Office of Ordinance, assigned a salary of 40 pounds per year and, in addition, a servant and 2 shillings per day when engaged on the King's business.
- Of course, military research always seems easier to fund and indeed the King seems to have seen Delamain as someone who would be able to construct machines of war.
- Frequent personal contact with the King led Delamain to believe that he might manage to secure a higher salary and he continually sought to increase his salary as well as more funds for building various different instruments.
- On 20 November 1638, the King appointed Delamain to an engineer's post at a salary of £100 per year with now 60 shillings per day extra when he was on the King's business.
- commanded Mr Herbert so give his son, the Duke of York (afterwards James II), his large ring calculating-dial, of silver, a jewel his Majesty much valued; it was invented and made by Mr Richard Delamain, a very able mathematician, who projected it, and in a little printed book did show its excellent use in resolving many questions in arithmetic, and other rare operations to be wrought by it in the mathematics.
- Delamain also emphasises that it is "fit for use ...
- Delamain and Oughtred had a bitter dispute over the invention of a circular slide rule.
- Delamain also published The Making, Description, and Use of ...
- In Delamain's we have two (or three) flat brass rings, of the same thickness, graduated and grooved on the edges, one moving within, and in contact with, the other: Oughtred's instrument consists of one round plate, divided into several concentric circles, on which are laid down the logarithms of numbers, sines and tangents, and all operations are performed by means of two indices, radiating from a pin at the centre, like the legs of a sector; this mode of operation, it must be obvious, is far more complex, more inconvenient, and more liable to derangement, than the simple movement first proposed by Delamain.
- Delamain argued with Oughtred, not only concerning the invention of the circular slide rule but also as regards the use of instruments in teaching mathematics.
- If we think in terms of modern instruments such as computers then one would have to say that Delamain's views have a ring of realism in today's world which are somewhat lacking in Oughtred's high ideals.
- It appears that Delamain's devotion to the King was essentially put on to further his career for, as soon as the Civil War broke out in 1642, he left the King's Court and joined the Parliamentary forces under Oliver Cromwell.

Born 1600, London, England. Died 1644, England.

View full biography at MacTutor

Origin England

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive