Nonius (device) explained

Nonius is a measuring tool used in navigation and astronomy named in honour of its inventor, Pedro Nunes (Latin: Petrus Nonius),^[1] a Portuguese author, mathematician and navigator. The nonius was created in 1542 as a system for taking finer measurements on circular instruments such as the astrolabe. The system was eventually adapted into the Vernier scale in 1631 by the French mathematician Pierre Vernier.^[2]

Technical features

The nonius was used to improve the astrolabe's accuracy. This consisted of a number of concentric circles traced on an instrument and dividing each successive one with one fewer divisions than the adjacent outer circle. On a standard scale of 90 degrees, there are an additional 44–45 concentric circles, with each divided into a specific unit size such that a scale unit on position

n had an arc of 90 /n degrees.^{[2] [3]} Thus, the outermost quadrant would comprise 90° in 90 equal divisions, the next inner would have 89 divisions, the next 88 and so on. When an angle was measured, the circle and the division on which the alidade fell was noted. A table was then consulted to provide the exact measure.^[4]

Applications

The astronomer Tycho Brahe applied the nonius to the astronomic quadrant.^{[5] [3]}

In numerically controlled machines, the nonius is part of several absolute encoders, that measure linear or rotational displacements.^[6]

See also

• Transversal (instrument making)

Notes and References

1. Web site: Pedro Nunes. Infopédia [em linha]. Porto: Porto Editora. 2015.
2. Poelje. Otto van. Diagonals and Transversals: Magnifying the Scale. Journal of the Oughtred Society. 25 July 2004. 22–28. 2 May 2017.
3. Web site: Eisele . Margarete . The Nonius . Mathematics in Europe . 2 May 2017 . ru-ru .
4. Web site: O conceito de nónio . António Estácio dos Reis . pt . Ciência Viva . The concept of Nonius . 17 January 2015 . https://web.archive.org/web/20150414094509/http://www.cienciaviva.pt/latlong/anterior/nonio2.asp . 14 April 2015 . dead.
5. Web site: Tycho Brahe recorre ao nónio de Pedro Nunes. António Estácio dos Reis. Ciência Viva. Tycho Brahe betakes Pedro Nunes' Nonius. 17 January 2015. https://web.archive.org/web/20150414093623/http://www.cienciaviva.pt/latlong/anterior/nonio3.asp. 14 April 2015. dead.
6. Web site: Nonius interpolation provides excellent differential linearity and higher resolution for linear displacement measurement systems or rotary encoders.