Note 466 — Chapter IV · THE SOURCES FOR THE PERIOD 1100–1250 A. D.

Roger Bacon, one of the most original thinkers of the entire medieval 409period in matters of natural science, was the last of a series of Englishmen who devoted themselves to these interests. In this group may be counted Adelard of Bath and, at a much later date, Alexander Neckam, Alfred of Sareshel, Daniel of Morley, and Robert Grosseteste (see above, p. 407, note 94). For the last-named, whose teachings in many particulars he adopted and elaborated upon, Bacon had the highest admiration.

Born about 1210–1215, Roger Bacon became a Franciscan between 1245 and 1250. His more important works were completed before 1266 and were condemned as heretical in 1278. He died in the last decade of the century. See Bridges, Life of Bacon, 1914, and Thorndike, Magic, 1923, vol. ii, pp. 616–691.

From the geographical point of view beyond all question the most important of Bacon’s writings was the Opus majus, which sets forth his fundamental ideas in the realms of natural and physical science. Bridges’ edition of this contains a full introduction and a detailed analysis of the text, chapter by chapter. The geographical material will be found in Part IV, on mathematical science. Distinctio ii of Part IV (Bridges’ edit., vol. i, 1897, pp. 109–119) is devoted to the subject of rays of light and emanations from the heavenly bodies and to the problem of the sphericity of the universe. Elsewhere in Part IV the influences of the heavenly rays upon the earth, especially in respect to zones, tides, and the healthfulness of situations, are brought out. Bacon here is largely indebted to Robert Grosseteste (see above, pp. 163–165). These theories are also worked out in some detail in the chapters of Part V (on optics) devoted to the multiplication of species (Bridges’ edit., vol. ii, 1897, pp. 539–543; Werner, Kosm. Roger Baco, 1879, pp. 597–599).

The last portion of Part IV (Bridges’ edit., vol. i, 1897, pp. 175–404), not divided into chapters, is a treatment of two broad subjects:

1. The importance of mathematics in relation to theology. Under this heading, among other points, there is given an explanation of how mathematics aids us in acquiring knowledge of the heavens, of the location of Paradise and of Hell, of sacred geography (that is of the positions and physical conditions of places spoken of in Scripture), of geometry (here the influence of mountains in reflecting the sun’s rays is elucidated; see above, pp. 179–180; Werner, op. cit., p. 599; Duhem, Système, vol. iii, 1915, p. 418), and of numbers (here are explained the size, distance, and relative magnitude of the heavenly bodies in relation to the earth and to the heavenly spheres).

2. The influence of the heavens on things terrestrial (Bridges’ edit., vol. i, 1897, pp. 286–403). According to Bacon geographic conditions are governed by astronomical and astrological forces. This part of the Opus majus shows first how the latter are effective in determining the conditions of habitability on the earth’s surface; it closes with a general description of the habitable earth (see especially Werner, op. cit., p. 545, note 4, and pp. 546–550, on Bacon’s astrological geography, and pp. 410600–606, on Bacon’s regional geography). Climata and the practical utility of knowledge of geography and of climates to the missionary are discussed. The description of the habitable earth is particularly full for Egypt, the Holy Land, India, Eastern Europe, Central Asia, and Cathay. Much fresh material regarding the Mongols and the Far East was derived from Bacon’s contemporaries, the Franciscan travelers John of Pian de Carpine and William Rubruck (see above, pp. 269–270). Bacon dismisses the geography of Western Europe as too familiar to require special treatment.

Besides the Opus majus, Bacon’s Communia naturalium and commentary on the Secretum secretorum include a few passages of interest to us. In the former the finite character of the universe is explained (Oxford edit., fasc., iv, pp. 369–373; see also, Opus tertium, Brewer’s edit., pp. 140–141), together with some consideration of the dimensions of heaven and of earth (Oxford edit., fasc. iv, pp. 414–418). In the latter (a book of miscellaneous precepts for the guidance of human affairs, which was many times translated from the Arabic during the Middle Ages and which was altered, augmented, and edited by Bacon) there is material on astronomy, on the size and sphericity of the earth, and on the relative extent of land and sea (Oxford edit., fasc. v).