After Professor Johannes Volmar's death in 1536, at the instigation of Philipp Melanchthon, Reinhold obtained the professorship of "Mathematum Superiorum" in the University of Wittenberg, which included astronomy, while his colleague Georg Joachim Rheticus became "Mathematum Inferiorum". Volmar had studied at Krakow and Wittenberg before moving to the University of Leipzig. He returned to Wittenberg where he was appointed as professor of mathematics in 1519. His most famous student was Joachim Rheticus. Philipp Melanchthon (1497-1560), Martin Luther's "right hand man", was a theologian, Greek professor and educator who reorganised the whole educational system of Germany, founding and reforming several of its universities. Melanchthon played a major role in getting both Reinhold and Rheticus appointed to teach mathematics and astronomy at the University of Wittenberg in 1536. Rheticus, however, spent the three years 1538-1541 away from Wittenberg, two of these years being spent with Copernicus.
Reinhold was elected dean in the college of arts, holding the position during the winter of 1540-41, and then dean in the college of philosophy during the summer of 1549. He became rector in the winter of 1549-50. This was a difficult time for those in Wittenberg which was a focal point of the Protestant Reformation which had begun in 1517 when Martin Luther nailed his 95 theses to the door of the castle in Wittenberg. Reinhold, like the majority of those in Wittenberg, was a Lutheran. The city was the capital of Saxony, ruled by the Elector of Saxony. The Schmalkaldic War of 1546-47 saw the Lutherans fighting against the Roman Catholic Emperor Charles I. When Charles I captured Wittenberg in 1547 the war was over and the Capitulation of Wittenberg was signed which compelled the Elector of Saxony to resign. Reinhold remained at the University attempting to continue his work during these dramatic events.
Reinhold, along with Rheticus, was one of the first scholars to draw attention towards the Copernican theories of heliocentrism in Germany. In his 1542 Theorciae novae Planetarum Ⓣ, he called Copernicus a "second Ptolemy, who restores the decaying building of education". However, Reinhold continued to recite Ptolemaic doctrine in his lectures. This might have been in part due to the theological establishment in Wittenberg, which considered Copernicus's model to be heretical, but Reinhold's comments on his own copy of Copernicus's De Revolutionibus Ⓣ seem to indicate that he was only interested in the mathematical aspects of the model and not in the cosmological theory.
The identification of Reinhold's annotations on his copy of De Revolutionibus Ⓣ was made by Owen Gingerich in 1970 when he examined the copy of De Revolutionibus Ⓣ held in the Royal Observatory in Edinburgh, Scotland. Here is Gingerich's description of this important discovery :-
I searched in vain for an owner's name. The manuscript inscriptions at the beginning and end provided nary a clue. Then I looked more closely at the heavy pigskin binding. ... Around the edges were long patterned strips with biblical figures. Below an empty central panel was the date 1543, and above the panel I noticed the initials ER. I reacted with shock. Could the initials stand for Erasmus Reinhold, the leading mathematical astronomer in the generation after Copernicus ... ? I seized a pencil and paper to make a rubbing of the dim impression and, to my dismay, found not two, but three, initials: ERS. It seemed my hypothesis had just evaporated. Back in Cambridge ... I soon discovered that those three initials, ERS, were exactly what was required for Erasmus Reinholdus Salveldiensis, for in the sixteenth century a man's birthplace - in this case Saalfeld - was a part of his formal designation. ... specimens [of Reinhold's handwriting] eventually confirmed my original deduction.The authors of  discuss the annotations made by Reinhold in this copy of De Revolutionibus Ⓣ:-
Reinhold's annotations are extensive and thorough: it is difficult to find an error in the text not already marked by him. Throughout, Reinhold proves remarkably aware of Copernicus's sources (such as Giorgio Valla, Johannes Werner, or Regiomontanus's 'Epitome'), even when Copernicus does not credit them explicitly. Reinhold sums up his approach to Copernicus's opus by a motto inscribed on the title page, a paraphrase of the chapter title I,4 'The Axiom of astronomy: Celestial motion is uniform and circular, or composed of uniform and circular motions'. There is nothing here about a revolutionary new cosmology, nothing about the earth orbiting like a planet about a stationary sun. Instead, Reinhold is fascinated by the use of pure circles to replace the Ptolemaic equant by an alternative mechanism. The marginalia throughout the volume verify this interpretation of Reinhold's interests. The cosmological chapter is virtually unglossed except for the correction of the periods of Venus and Mercury. Book III, concerning the precession and the relative motion of the earth and the sun, in contrast to the cosmological sections is generously annotated. Several long glosses discuss chronology. Others concern the observational basis for precession and the obliquity, where Reinhold regularly includes Johannes Werner, an antagonist whom Copernicus assiduously avoids mentioning.The University of Wittenberg lacked an observatory so Reinhold had to make do with a wooden quadrant. He did publish some ephemerides, but most of his work was not observational. As stated above, he published a commented edition of Georg van Peurbach's (1423-1461) Theorciae novae Planetarum Ⓣ, which was still at use in many universities, in 1542. In his comments, he showed that the orbits of Mercury and the Moon describe an oval figure and he makes the first published description of a camera obscura. In 1549, he published the first book of Ptolemy's Almagest in Greek with a Latin translation, under the title Ptolomaei Mathematicae constructionis liber primus Ⓣ. In his dedication of this work Reinhold wrote:-
For the advantage and happiness of the public schools, I began an edition of Ptolemy's excellent work, in which the universal theory of heavenly motions is raised on its first foundations. The present edition of the first book is aimed at making students familiar with the basics of astronomy, which are preliminary to a correct understanding of the other books of the 'Almagest'. Without any doubt, it is very useful to present to young people these sources of the discipline. Still, since beginners are not yet conversant with the Greek language, I have added a Latin translation, for whose inaccuracy I beg the pardon of the experts. I also hope that somebody will eventually accomplish a complete and clear translation of Ptolemy for public interest. Moreover, to help students, I have commented and explained some difficult passages. I hope that all these efforts will be pleasing to God and that all experts will approve them. My intention is, in fact, that the young will not strive merely for the empty shadow of the doctrine, but that they are made familiar with mathematics and with this art that is useful for human life and peace.He intended to finish this work, but his early death did not allow him. Posthumously, in 1554, his Primus liber Tabularum Directionarum Ⓣ was published, an improvement of Regiomontanus's trigonometric tables that includes the sines for every minute of the quadrant. He also teaches students how to use the tables to solve spherical problems.
Reinhold was dissatisfied with the tables included in Copernicus's De revolutionibus Ⓣ, so he decided to remake them in a more useful form. For this project, he found a patron in Duke Alfred of Prussia. In 1551, after seven long years of work, he published his Prutenicae Tabulae Coelestium Motuum Ⓣ. They were a series of astronomical tables that showed that the heliocentric model was applicable in practice. They remained the most important resource for astronomical calculation until Kepler's Tabulae Rudolphinae Ⓣ (1627). A testament of their importance is the fact that they received four printings in thirty-five years: in 1551, 1562, and 1571 in Tubingen, and in 1585 in Wittenberg. He wrote in the tables (see ):-
Copernicus, the most learned man whom we are able to name other than Atlas and Ptolemy, even though he taught in a most learned manner the demonstrations and causes of motion based on observation, nevertheless fled from the job of constructing tables, so that if anyone computes from his tables, the computation is not even in agreement with his observations on which the foundation of the work rests. Therefore first I have compared the observations of Copernicus with those of Ptolemy and others as to which are the most accurate, but besides the bare observations, I have taken from Copernicus nothing other than traces of demonstrations. As for the tables of mean motion, and of prosthaphaereses and all the rest, I have constructed these anew, following absolutely no other reasoning than that which I have judged to be of maximum harmony.Reinhold married twice: first with Margaretha Bauer (died 7 October 1548), the daughter of a burgher from Saalfeld, on 22 January 1537; and later with Martha (died 1552) in 1550. Both of his wives died in childbirth. His first marriage gave him a son, also named Erasmus (1538-92). He also had two daughters, Margareta and Katharina. Erasmus Jr :-
... studied mathematics and medicine in Wittenberg under the care of Melanchthon, and then in Jena, and became doctor of medicine and municipal doctor in Amberg and Saalfeld. Later he became 'mountain steward' to the Elector of Saxony, and wrote works on land surveying as well as calendars, which appeared regularly for many years in Erfurt.In 1552, Reinhold moved to stay with his parents in Saxony, fleeing from the bubonic plague, but he eventually succumbed to it. His last words were "Vixi et quem dederas cursum mihi, Christe, peregi" Ⓣ. His student, Kaspar Peucer (1525-1602), succeeded him as professor of mathematics in Wittenberg in 1554.
In 1575, Tycho Brahe visited Reinhold's son in Wittenberg and studied his annotated copy of the De Revolutionibus Ⓣ. Reinhold's notes inspired Brahe to consider alternative arrangements of planetary circles that led to his own geo-heliocentric system. In fact Christoph Rothmann, court mathematician of Kassel, wrote in 1588 when Brahe published De mundi aetherei recentioribus phaenomenis Ⓣ:-
I did not consider this geo-heliocentric theory to be a new approach but precisely Copernicus's, apart from the fact that I could treat the matter in the reverse manner by bringing Copernicus's hypotheses back to the solar motion. Moreover, I assumed that Rheticus and Reinhold also took that same approach into consideration.
Article by: I J Falconer, J G Mena, J J O'Connor, T S C Peres, E F Robertson, University of St Andrews.