**Nicolaus Mercator** was a German mathematician best known for his series for log(1 + *x*).

- In 1648 Mercator moved to the University of Copenhagen.
- Probably in the same year Mercator published a text De emendatione annua diatribae duae Ⓣ(Correction to the distribution of days in the year) in which he argues for a new version of the calendar in which there are 12 months with 29, 29, 30, 30, 31, 31, 32, 31, 31, 31, 30, 30 days respectively.
- After working at the University of Copenhagen for six years, Mercator had to leave when the university was closed due to the plague.
- Three letters exchanged between Boulliau and Mercator, concerning the famous transit observation of Horrocks, symbolically link three distinct phases of post-Keplerian thought.
- Boulliau, although rejecting Kepler's area rule and his vision of a celestial dynamics, became known in the middle decades of the seventeenth century as the leading proponent of elliptical orbits; whereas his younger correspondent, Mercator, author of several mathematical and astronomical texts, argued the superiority of the Keplerian ellipse and area rule over rival elliptical hypotheses in the latter half of the century.
- Mercator went to England some time before 1660, almost certainly in an attempt to improve his fortunes.
- We do know that Cromwell was aware of Mercator proposals for changing the calendar and some historians suggest that Cromwell may have invited Mercator to England.
- Certainly Mercator would have liked to have received a university appointment but, unable to find such a position, he did private tutoring in London.
- Mercator invented such a marine chronometer, a pendulum clock, and on the strength of this invention he was elected a Fellow of the Royal Society in November 1666.
- In the following year of 1669, at the request of Collins and Seth Ward, Mercator translated the Dutch text Algebra ofte Stel-konst Ⓣ(Algebra of sets and numbers) by Kinckhuysen into Latin.
- This brought Mercator into contact with Newton and the two men exchanged letters, discussing among other things the motion of the moon.
- Mercator published a further two volume work in astronomy Institutiones astronomicae Ⓣ(Astronomical institutions) in 1676.
- One might have thought that Mercator's reputation was sufficient that he would have been able to acquire a good post but it seems that he could not.
- In 1676 Hooke proposed Mercator for the post of Mathematical Master at Christ's Hospital, but he was not appointed.
- Jean-Baptiste Colbert, founder of the Académie des Sciences in Paris in 1666 and controller general of finance in France, had invited Mercator to undertake the project.
- Unfortunately Mercator fell out with Colbert so this project was not a success.
- There is some reason to confuse Nicolaus Mercator with Gerardus Mercator since Nicolaus also worked on Gerardus's map projection.

Born 1620, Eutin, Holstein, Holy Roman Empire (now Germany). Died 14 January 1687, Paris, France.

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Astronomy, Origin Germany, Number Theory, Special Numbers And Numerals

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