Christmann, Jacob

(b. Johannesberg, Rheingau, Germany, November 1554; d. Heidelberg, Germany, 16 June 1613),

oriental studies, mathematics, chronology, astronomy.

Christmann studied oriental subjects at Heidelberg and became a teacher there in 1580. Shortly thereafter, however, he had to leave that university because he, as a Calvinist, could not subscribe to the concordat-formulary set down by the Lutheran Elector Ludwig VI. Christmann traveled for some time, then settled down to teach in a Reformed school in Neustadt, Pfalz. He was a teacher there in 1582. The death of Ludwig (12 October 1583) enabled him to return to Heidelberg, where he was appointed professor of Hebrew on 18 June 1584. From 1591 on he taught Aristotelian logic. He was made rector of the university in 1602.

In 1608 Frederick IV appointed Christmann professor of Arabic. Christmann thus became the second teacher of that subject in Europe, the first having been Guillaume Postel at Paris in 1538. This appointment must have given great satisfaction to its recipient, since in 1590, in the preface of his Alfragani chronologica et astronomica elementa, Christmann had advocated the establishment of a chair of Arabic “to open possibilities for teaching philosophy and medicine from the [original] sources,” Indeed, Christmann had demonstrated his scholarly interest in the Arabic language as early as 1582, with the publication of his Alphabeticum Arabicum, a small book of rules for reading and writing Arabic. Besides Arabic, he is said to have known Syrian, Chaldaic, Greek, Latin, French, Italian, and Spanish. He was an extremely modest man despite his learning, with a passion for work that may well have hastened his death of jaundice.

On the death of Valentine Otho, Christmann inherited the entire library of G. J. Rhäticus, which had been in Otho’s keeping. This collection contained trigonometric tables more extensive than those that Rhäticus had published in the Opus Palatinum of 1596 (adapted by B. Pitiscus as the basis for his Thesaurus mathematicus of 1613) as well as the original manuscript of Copernicus’ De revolutionibus orbium coelestium. The inclusion of instruments in the bequest stimulated Christmann to begin making astronomical observations. In 1604 he proposed to Kepler that they should exchange the results of their researches. Christmann was the first to use the telescope in conjunction with such instruments as the sextant or Jacob’s staff (1611), with the results reported in his Theoria lunae and Nodus gordius. These last works also show him to be a competent astronomical theorist. He gave a good treatment of prosthaphaeresis, the best method of calculating trigonometric tables to be developed before the invention of logarithms, which he based on such formulas as

2 sin α sin β = cos (α – β) – cos (α + β);

he then went on to prove that this method had been devised by Johann Werner.

In his Tractatio geometrica de quadratura circuli, Christmann defended against J. J. Scaliger the thesis that the quadrature of the circle could be solved only approximately. In his books on chronogly—a topic of great concern at a time of radical calendar reform—he disputed the work of not only Scaliger but also J. J. Lipsius. He further criticized Copernicus, Tycho, Brahe, and Clavius—some such criticisms may be found in some detail in manuscript annotations of his own copy of Alfragani chronologica et astronomica elementa, which is now in the library of the University of Utrecht.

BIBLIOGRAPHY

I. Original Works. Christmann’s works are Alphabetum Arabicum cum isagoge scribendi legendique Arabice (Neustadt, 1582); Epistola chronologica ad Iustum Lipsium, qua constans annorum Hebraeorum connexio demonstratur (Heidelberg, 1591; Frankfurt, 1593); Disputatio de anno, mense, et die passionis Dominicae (Frankfurt, 1593, combined with the 2nd ed. of Epistola); Tractatio geometrica, de quadratura circuli (Frankfurt, 1595); Observationum solarium libri tres (Basel, 1601); Theoriae lunae ex novis hypothesibus et observationibus demonstrata (Heidelberg, 1611); and Nodus gordius ex doctrina sinuum explicatus, accedit appendix observationum (Heidelberg, 1612).

He translated from a Hebrew translation and commented on Muhamedis Alfragani Arabis chronologica et astronomica elementa, additus est commentarius, qui rationem calendarii Romani… explicat (Frankfurt, 1590, 1618) and translated and commented on Uri ben Simeon, calendarium Palaestinorum (Frankfurt, 1594). He edited, with translation and comments, Is. Argyri computus Graecorum de solennitate Paschatis celebranda (Heidelberg, ca. 1612).

II. Secondary Literature. On Christmann’s life, see Melchior Adam, Vitae Germanorum philosophorum (Heidelberg, 1615), pp. 518–522; on his Arabic studies, Johann Fück, Die arabischen Studien in Europa (Leipzig, 1955), pp. 44–46; on his instruments, H. Ludendorff, “Über die erste Verbindung des Fernrohres mit astronomischen Messinstrumenten,” in Astronomische Nachrichten, 213 (1921), cols. 385–390; on the propthaphaeresis, A. von Braunmühl, Vorlesungen über Geschichte der Trigonometric, I (Leipzig, 1900), see index. See also Daniël Miverius, Apologia pro Philippo Lansbergio ad Jacobum Christmannum (Middelburg, 1602); and J. Kepler, Gesammelte Werke (Munich, 1949–1954), esp. II (1939), 14–16—XV (1951). 41 f., gives a letter from Christmann to Kepler, dated 11 April 1604 (old style).

J. J. Verdonk