Peter, in Spanish Nunez, a learned Portuguese, and one of the most able mathematicians of the sixteenth century, was born at Alcaer. He was preceptor to Don Henry, son of Emmanuel, and taught mathematics in the university of Coimbra. He published the following works, by which he gained great reputation, viz. 1. De Arte Navigandi; 2. Annotationes in Theorias Planetarum Purbachii, which are greatly esteemed; 3. A treatise De Crepusculis; 4. A treatise on Algebra. It is observed in Furetière's Dictionary, that Peter Nonius, in 1530, first invented the angles of 45 degrees made in every meridian, and that he called them rhumbs in his language, and calculated them by spherical triangles. Nonius died in 1577, aged eighty.

name given to the common device for subdividing the arcs of quadrants and other astronomical instruments, from the persuasion that it was invented by the above-named Nonius or Nunez. The generality of astronomers, however, transferring the honour of the invention from Nunez to Peter Vernier, a native of Franche Comté, have called this method of division by his name. But Mr Adams, in his Geometrical and Geographical Essays, has shown that Clevius the Jesuit may dispute the invention with both of them. The truth seems to be, that Nunez started the idea, Clevius improved it, and Vernier carried it to its present state of perfection. The method of Nunez, described in his treatise De Crepusculis, printed at Lisbon in 1542, consists in describing within the same quadrant 45 concentric circles, dividing the outermost into 90 equal parts, the next within into 89, the next into 88, &c. till the innermost was divided into 46 only. On a quadrant thus divided the plumb-line or index must cross one or other of the circles very near a point of division; and hence, by computation, the degrees and the minutes of the arch may be easily ascertained. This method is also described by Nunez in his treatise De Arte atque Ratione Navigandi, where he would fain persuade himself that it was not unknown to Ptolemy. But as the degrees are thus divided very unequally, and as it is very difficult to attain exactness in the division, especially when the numbers into which the arches are to be divided are incomposite, the method of diagonals, first published by Digges, in a treatise entitled Alex seu Scala Mathematica, printed at London in 1573, and said to be invented by one Richard Chenseler, was substituted in its stead. Nonius's method, however, was improved at different times and by different persons; and it must be acknowledged, that if Vernier saw either the original or any of the improvements (and there can be little doubt of his having seen them all), his merit consists only in having applied to an useful practical purpose the speculative invention of another person.