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John of Saxony

John of Saxony

(fl. France, first half of the fourteenth century)


Probably from Germany, John Dank, Danco, Danekow, or Danekow of Saxonia was active in science at Paris between 1327 and 1335; 1 but his scientific career may possibly have begun as early as 1297. John of Saxony, who considered himself a student of John of Lignè res, composed various works on the Alfonsine tables or works that employed them and a commentary on the astrological treatise of al-Qabisi (Alcabitius).

In 1327 John of Saxony published canons on the Alfonsine tables: “Tempus est mensura motus ut valt Aristoteles. . . 2 An exact appreciation of the place of these canons in the history of astronomy is dependent on knowledge of the introduction of the Alfonsine tables that the tables were already known to William of Saint-Cloud in 1300; 3 but his conclusions are based on an unsound subdivision of poorly identified texts (see the article on John of Murs), and it seems unlikely that the tables were known in Paris before about 1320. Their first appearance in medieval science may have been in the Expositio tabularum Alphonsi regis Castelle, written by John of Murs in 1321, and in the canons of the tables (1322) by John of Ligné res. These canons, however, do not apply to the Alfonsine tables in the form known in the Latin West at the end of the Middle Ages. A short time later, in face, the Alfonsine tables underwent a considerable transformation affecting both form and substance—the form through substitution of a sexagesimal representation of the mean movements of the plantes for the traditional mode employing anni colleci and anni expansi, the substance through adoption of a double eccentricity for the eqution of Venus and Jupiter. It is to this new drafting of the Alfonsine tables that the following canons apply: the undated “Quia ad inveniendum loca planetarm. . .” of John of Lignè res; the canons of John of Saxony of 1327; and the canons “Prima tabula docet differentiam . . .” of John of Murs (1339).

It may be wondered why these three astronomers, who very likely worked together, produced text on the same subject that duplicate one another. Basically, these texts deal with the same tabular material and defend the same principles, particularly in regard to the movement of planetary apogees. John of Lignè res’s very succinct account deals only with changes of ca; lendar and with determining the mean solar and lunar conjunctions and oppositions and computing the true place of the planets. John of Saxony developed this account; his canons are clearer, and he added chapters on finding a “revolution” (the moment when the sun returns to a previously occupied position); calculating the date and hour of a true conjunction of the sun and moon and go their position “in quarter aspect” determining the time of the entrance of the sun into one of the signs of the zodiac; establishing the date of the conjunction of two planets. John of Saxony’s canons enjoyed considerable success, attested to by the number of extant manuscripts and by their inclusion in the first printed edition of the Alfonsine tables (1438); the canons of John of Lignè res, like those of John of Murs, were never printed.

Produced through the efforts of Erhard Ratdolt, this first printed edition bears, following John of Saxony’s canons, the words “Expliciunt canones et quod sequitur est additio.” This supplement comprises a general remark on interpolation in the tables of equations, canons of the eclipses, and several chapters —preceded by a separate title page—on the latitudes of the planets. The canons of the eclipses (ldquo; Eclypsis soils quantitatem et durationem. . .” ) are also credited by the manuscripts to John of Saxony. Consequently, they complete the chapter on determining the true conjunctions of the sun and moon and are designed to accompany particular tables which appear at the end of the Alfonsine tables and were not part of the first group. John of Saxony’s canons of eclipses duplicate those of John of Lignè res for the tables of 1322, not the canons “Quia ad inveniendum. . .,” which do not treat eclipses. A manuscript of the canons of John of Saxony attributes the date 1330 to them.4

Another way in which John of Saxony participated in efforts to spread knowledge of the astronomial tables was in his working out of examples in the Exempla super tabulas et canones primi mobilis of John of Lign′ res. The work is not, properly speaking, a commentary but a collection of numerical applications, developed in a pedagogial fashion, of the canons of John of Lignè res on the canons of the primum mobile, “Cujuscuque arcus propositi. . .,” that is, of the portion of the canons of 1322 dealing with astronomical trigonometry. According to a note in MS Pá ris lat. 7281,5 it was believed that these exempla appeared simultaneously under two incipits, “Non fuit mortuus qui scientiam vivificavit. . .” and “Quia plures astrologorum diversos libros. . .,” with the date 1355; but this note has been misinterpreted. The author of the manuscript, which in the middle of the fifteenth century constituted a collection of the thirteenth- and fourteenth-century astronomical texts, merely wished to indicate that there existed, under the incipit “Non fuit mortuus. . .,” a collection of examples at Paris dated 1356 (and not 1355), dealing with the canons of astronomical tables; the information is correct, the texts thus explained being the canons of the Alfonsine tablets published by John of Saxony in 1327. These examples are found in particular in the manuscripts Paris lat. 7407, fols. 1-26v, and Paris lat. 15104, fols. 122v-137 and 122. Nothing, however, indicates that the examples of 1356 are also by John of Saxony,6 As for the applications of the canons of the primum mobile ( “Quia plures astrologorum. . .” )—the only ones formally attributable to John of Saxony—they do not include dated examples, since, for the purpose of these canons, they were not needed. The only example from which chornological information might be drawn is one which concerns the star Aldebaran, whose movement since the determination of athe Alfonsine coordinates is estimated at 51é: the movement of the apogees and of the sphere of the fixed stars is too slow for this information to be interpreted with precision; it corresponds approximately to the year 1335.

The astronomical tables provide a general means of determining the positions of the planets at all times and in all locations, but they do not give these positions themselves. The calculations for establishing the latter are, moreover, long and tedious. In order to prevent their character from turning young people away from astronomy, John of Saxony did the calculations in advance, compiling an ephemeris for the period 1336-1380 and for the meridian of Paris with a short canon: “Cum animadverterem quamplurimos magistros et scholars in Studio Parisiensi. . ..” 7 The basis for the calculations is obviously the Alfonsine tables.

In 1331 John of Saxony wrote a commentary on the great astrological treatise of al-Qabisi known under the title Liber isagogicus. Printed in 1485, at the same time as al-Qabisi’s work, which had already reached its third edition, this commentary is found very frequently in the manuscripts. Although he himself is confident of the possibilities of astrology, especially in meteorology, John of Saxony distinguishes between his own specialty and the domain of faith, taking care not to encroach upon the latter.

Medieval manuscripts and modern scholars have credited John of Saxony with all kinds of astronomical and astrological texts; the majority are only extracts of canons on the Alfonsine tables or on taobles of the eclipses. For the remainder, the attribution is suspect, to say the least:there is no evidence for affirming, for example, that he wrotoe the astrological commentary concerinig a person born on 10 March 1333 at a place situated at 52° latitude and 3° east of Paris.8 The exempla of 1356 on the canons of the Alfonsine tables had no relation to him. The treatise on the astrolabe attributed to John ofo Saxony by MS Erfurt 4°366, fols. 82-85v ought to be assigned to John of Seville. Finally, another John of Saxony was responsible for texts of a medical nature—which, moreover, date from a later period.9

Two manuscripts attribute to John of Saxony a computus dated 1297 ( “Omissis preternecessariis cum intentionis sit. . .” ) and a commentary on it. Since the date appeared incompatible with a chronology which would have extended his period of activity to 1355, Duhem and Thorndike concluded that a homonymous author was involved, unless the date is corrected to 1397 (which settles nothing) of 1357. But the date of 1297 is confirmed by technical data furnished by the text (year of indiction 10 and golden number 6); and since his career is not known to extend beyond 1335, there is no major objection to supposing that John of Saxony wrote on the computus thirty years before publishing canons on the Alfonsine tables, the introduction of which had occurred during the intervening period. The author of the computus, who identifies himself as Johannes Alemanus, is concerned with the longitudes of Paris and Magdeburg; the latter is given as the native city of John of Saxony by one of the manuscripts of his canons on the Alfonsine tables.10

If the attribution of the computus of 1297 to John of Saxony is accepted, then it follows that he was considerably older than John of Murs, whose scientific activity extended from 1317 (his first work also concerns the calendar) to after 1345. Moreover, since John of Saxony acknowledged that he was the student the three John of Ligné res, who wrote between 1320 and 1335, the three Johns who made such a profound mark on fourteenth-century astronomy may be arranged in the following sequence of birth: John of Ligné res, John of Saxony, and, about twenty years later, John of Murs.


1. Ms Berlin F.246, fol. 121, which dates from 1458, calls John of Saxony “magister J. de Saxonia alio nomine magister Johnnes Danekow de Magdeborth.” MS Paris lat. 7281 calls him both John of Saxony and John of Counnout; P. Duhem (Le systé me du monde, IV , 78) has erected daring hypotheses on the basis of this. It is sufficient to observe that, while the MS Paris lat. 7281 is an exceptionally valuable document for the history of astronomy because of the variety and quality of the texts that it unites, and while it demonstrates its author’s fine curiosity with regard to texts, many of which were then out of date, it is still a late testimony (mid-fifteenth century) and contains certain misinformation.

2. The date, furnished by many explicits in the MSS , is confirmed by the example of 3 July 1327, given in connection with the expression of dates in sexagesimal numeration.

3. Duhem, op. cit., pp. 20-24.

4. Brussels 1022-47, fols. 37-39v; the incipit is somewhat different—“Ad eclipsim soils inveniendam quere primo conjonctionem. . . —but the text is the usual one.

5. Paris lat. 7281, fol. 222: “Canones cum exemplis particularibus ad longum ‘ Noin fuit mortuus quiscientiam vivificavit etc.’; ponountur exempla in omnibus canonibus super radicem anni Christi 1355 completi et super Parisius” (note misread by Duhem,op. cit., p. 78, and by Thorndike, A History of Magic. . ., III, 225).

6. Despite the account, erroneous on this poinit, of simon de Phares (E. Wickersheimer, ed., p. 216): “et first une declaracion bien ample sur les mouvements des planets qui se commence ‘ Non fuit mortus.’”

7. In a pharse which apears to make of it a doublet from “Tempus est mensura motus. . .,” imon de Phares (ibid.) points out this incipit, thus deformed “Quaplures astrorum diversos. . ..”

8. Thorndike, op. cit., p.267. The text is in Oxford, Hertford Coll. 4, fols. 126-130v: “Investigations gradus ascendentis nativitatis. . .,” followed, in fols. 131-133v, by another commentary: “In hac onativitate sic processi. . .,” not dated, but in which the planetary positions allow us to refer to 17 March 1308 for 55° latitude; they concern two particular applications of a general rule for determining the ascendant at the moment of birth. The other MS cited by Thorndike, Vienna 5296, fols. 23-25, contains another application, to a person born on 28 September 1444, as does MS Catania 85, fols. 251-253.

9. E. Wickerdheimer, Dictionnaire biographique des mé decins en France au moyen âage (Paris, 1936), p. 475.

10. See note 1.


I. Original Works.The 1327 canons on the Alfonsine tables and the canons of the eclipses composed by John of Saxony were printed at Venice in 1483, with the Alfonsine tables (Klebs 50.1); the MSS containing these texts number in the hundreds. The Exempla super. . . canones primi mobilis may be found in the following MSS : Erfurt F.3886, fols. 26-32; Paris lat. 7281.fols.222-232; Paris lat. 7285, fols. 30-36; Paris lat. 7407. fols. 27-40. The ephemeris of 1336-1380 is preserved in MSS Erfurt F. 386, fols. 62-108; canons).

The commentary on the Liber isagogicus of al-Qabisi was printed with the latter in 1485 (Klebs 41.3) and several times afterward. See B. Boncompagni, “Introno all vite inedite di tre matematici. . .,” in Bullettino di bibliografia e di storia delle scienze matematiche e fisiche, 12 (1879), 373-374. There are numerous MSS.

The computus of 1297 is preserved in MS Florence Plut. 30.24, fols. 78-86; the commentary on this computus ( “Sicut dicit Ptolomeus in Almagesti disciplina. . .” ) is found followiing the above text in the same MS, fols.87-96v; and in Erfurt 4° 365, fols.132-139.

II. Secondary Literature. P. Duhem, Le systé me du monde, IV (Paris, 1916), 76-90; and L. Thorndike, A History of Magic and Experimental Science, III (New York, 1934), 253-267, must be corrected on man y points.

Emmanuel Poulle

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