APPENDIX I
THE PERSPECTIVE OR OPTICS OF WITELO
Emphasis upon experimental method.
In the work on the science of Perspective or Optics, which was composed later in the thirteenth century by Witelo[1496] who calls himself a son of Thuringians and Poles,[1497] we meet again with much the same attitude as that shown in the corresponding works of Grosseteste. The experimental character of the subject is repeatedly emphasized;[1498] we hear much of experimenting with instruments;[1499] and such words as “experimenter” and “experimentation” are used.[1500] Similar passages, however, are also found in Witelo’s main source, the work of the Arab Alhazen on the same subject.[1501] But Witelo also encourages his readers to go farther and experiment for themselves, assuring them that “experience more than books will teach the varied possibilities of images”[1502] from mirrors, suggesting, “Let then the ingenuity of moderns and men of the future add what it shall please,”[1503] and again affirming in the case of burning-glasses, “But in experimentation with these too there is the greatest latitude which we leave to those who are curious in such matters.”[1504]
Occult and astral virtue.
Witelo also resembles Grosseteste in his favorable attitude toward astrology and the conception of the radiation of virtue. Already in his preface to William of Moerbeke he speaks of that “influence of divine virtues which is made in marvelous wise in inferior bodies through the virtues of superior bodies,”[1505] of that “divine light” which is “the sensible medium of corporal influences,”[1506] marvelously assimilating and connecting inferior bodies with superior bodies, while he compares the influence of the celestial constellations upon subject bodies to the process of reflection in a mirror.[1507] At the beginning of his tenth book, stating that the virtues of natural forms increased by refraction act more strongly, he adds that universally an increase of the virtue of the rays of the stars or of other forms at the same natural point or about the same point results in stronger action. Such passages suggest that perspective or optic was studied not only for its own sake but for its supposed analogy to the operation of occult and astral virtue. Indeed in his preface he represents William of Moerbeke as versed in such occult research,[1508] and William translated not only astrological treatises but also probably the so-called Ptolemaei de speculis which is really Hero’s Catoptrica. Baeumker believes that Witelo for his part was strongly affected by the metaphysical theory in favor with the Neo-Platonists and Gnostics of primitive light as the origin of intelligence, space, and so on.
Marvelous effects.
In Witelo’s work may also be noticed something of that element of thaumaturgy which we noted in Hero of Alexandria. Thus in his eighth book on concave mirrors he speaks of the “marvelous diffusion of natural forms and the multiform deception of the visions beheld,” while in the ninth book on burning glasses we are promised the production of astonishing effects. But as a rule Witelo’s presentation of his subject is geometrical rather than sensational, and his first book, not paralleled in Alhazen, is a geometry of 137 propositions as a basis for the ensuing “universal axioms of this science.” As we have seen, however, Witelo employs the experimental as well as the mathematical method and instruments as well as theorems.
Further characteristics.
Unlike Grosseteste, Witelo regards vision by extramission of rays from the eye as impossible,[1509] wherein he follows Alhazen. Of magnifying lenses he seems to display only a theoretical knowledge,[1510] and to add little to Alhazen on this point and less to Grosseteste. In general, however, he is believed by collecting the tradition of the past and filling in the gaps therein to have made the whole subject clearer to the Latin world and to have produced a work which served for several centuries as an excellent text book in the field of optical science.[1511] Its original portion consists especially of observations made by the author at Padua and Viterbo,[1512] which latter town was also the scene of several of William of Moerbeke’s translations. The Perspective was probably dedicated to him about 1270.[1513]
[1496] I have used the edition of 1572, Vitellionis Thurinopoloni Opticae libri decem, ed. F. Risner, Basel, 1572, where the text of Witelo, occupying 474 pages, is preceded by a Latin translation of Alhazen in 288 pages. The chief modern study on Witelo is C. Baeumker, Witelo, ein Philosoph und Naturforscher des XIII Jahrhunderts, Münster, 1906.
[1497] In his preface to William of Moerbeke. “Veritatis amatori fratri Guilielmo de Morbeta vitello filius thuringorum et polonorum....”
[1498] II, 43, “Experimentaliter etiam et hoc propositum theorema potest declarari ...;” II, 46, “Sed et id quod nunc proponitur potest experimentaliter declarari ...;” X, 43, “Hoc autem potest sic experimento declarari ...” etc.
[1499] II, 42, “Huius propositionis probatio plus experientiae instrumentorum innititur quam alteri demonstrationum. Cum ergo quis experiri voluerit....” II, 44, “Instrumentaliter similiter experientia propositum theorema potest declarari....” II, 45, “Hoc quod nunc hic proponitur est conformiter prioribus per instrumentalem experientiam declarandum....” II, 47, “Illud quod particularibus experientiis hactenus instrumentaliter probatum est naturali demonstratione.... intendimus.... adiuvare....”
[1500] See especially IV, 108.
[1501] Compare Witelo IV, 108 and X, 5 with Alhazen III, 12 and VII, 10.
[1502] IX, 35, “et plus experientia quam scriptura docebit imaginum diversitates....”
[1503] IX, 35, “Ingenium vero modernorum et futurorum addat quod libuerit....”
[1504] X, 48, “Sed et in horum experimentatione est maxima latitudo quam relinquimus ad talia curiosis.”
[1505] “... divinarum virtutum influentiam inferioribus rebus corporalibus per virtutes corporales superiores modo mirabili fieri....”
[1506] “Corporalium vero influentiarum divinum lumen sensibile est medium.”
[1507] “Et dum sic per figuras speculorum discurrimus celestes et omnes naturales influentias a subiectis corporibus sub quodam reflexionis modo ad alia corpora declaramus.”
[1508] “Placuit tibi in illius rei occulta indagine versari,” in the 1572 edition; but in Quetif-Echard (1719) I, 389, “in illius rei occultae indagine.”
[1509] III, 5-6.
[1510] X, 43 et seq.
[1511] Baeumker (1908), p. 237.
[1512] Ibid., p. 224.
[1513] Such is Baeumker’s opinion; why Dr. Charles Singer in his lecture on “Science” in Medieval Contributions to Modern Civilisation, (p. 140), speaks of Witelo as “the earliest” of the group of forward-looking scientific thinkers which culminated in Roger Bacon and dates him “(c. 1250)” I do not know.