Three men stand out in this period as devotees of science: Adelard of Bath, Albert the Great, and Roger Bacon.

Adelard, after studying in many Moslem countries, returned to England and wrote (c. 1130) a long dialogue, Quaestiones naturales, covering many sciences. It begins Platonically by describing Adelard’s reunion with his friends. He asks about the state of affairs in England; he is told that the kings make war, judges take bribes, prelates drink too much, all promises are broken, all friends are envious. He accepts this as a genial summary of the natural and unchangeable condition of things, and proposes to forget it. His nephew inquires what has Adelard learned among the Moslems? He expresses a general preference for Arabic as against Christian science; they challenge him; and his replies constitute an interesting selection from all the sciences of the age. He inveighs against the bondage of tradition and authority. “I learned from my Arabian masters under the leading of reason; you, however, captivated by… authority, follow your halter. For what else should authority be called than a halter?” Those who are now counted as authorities gained their reputation by following reason, not authority. “Therefore,” he tells his nephew, “if you want to hear anything more from me, give and take reason…. Nothing is surer than reason… nothing is falser than the senses.”88 Though Adelard relies too confidently on deductive reasoning, he gives some interesting replies. Asked how the earth is upheld in space, he answers that the center and the bottom are the same. How far would a stone fall if dropped into a hole bored through the center of the earth to the other side?—he answers, Only to the center of the earth. He states clearly the indestructibility of matter, and argues that universal continuity makes a vacuum impossible. All in all, Adelard is a brilliant proof of the awakening intellect in Christian Europe in the twelfth century. He was enthusiastic about the possibilities of science, and proudly calls his age—the age of Abélard—modernus,89 the climax of all history.

Albertus Magnus had a little less of the scientific spirit than Adelard, but so cosmic a curiosity that the very immensity of his product won him the name Great. His scientific, like his philosophical, works took mostly the form of commentaries on the corresponding treatises of Aristotle, but they contain now and then fresh breaths of original observation; amid a cloud of quotations from Greek, Arabic, and Jewish authors he finds some opportunities to look at nature in the first person. He visited laboratories and mines, studied diverse metals, examined the fauna and flora of his native Germany, noted displacements of land by sea, sea by land, and explained thereby the fossil shells in rocks. Too much of a philosopher to be a thorough scientist, he allowed a priori theories to color his vision, as when he claimed to have seen horsehairs in water change into worms. But, like Adelard, he rejected the explanation of natural phenomena in terms of the will of God; God acts through natural causes, and man must seek Him there.

His notion of experiment was obscured by his confidence in Aristotle. A famous passage in Book X of his De vegetabilibus stirs us with the words Experimentum solum certificat, which seems to say that “only experiment gives certainty.” But the wordexperimentum had then a broader meaning than now; it meant experience rather than experiment, as appears from the context of the passage: “All that is here set down is the result of our own experience, or has been borrowed from authors whom we know to have written what their personal experience has confirmed; for in these matters experimentum solum certificat.” Even so, it was a wholesome advance. Albert laughs at such mythical creatures as the harpies or the griffin, and the animal legends of a then popular book, thePhysiologus, and he notes that “philosophers tell many lies.”90 Sometimes, not often, he performed experiments, as when he and his associates proved that a beheaded cicada continued for a while to sing. But he trusted Pliny’s authority with saintly innocence, and believed too simply the tales told him by such notorious liars as hunters and fishermen.91

He yielded to his times in accepting astrology and divination. He attributes marvelous powers to gems and stones, and claims to have seen with his own eyes a sapphire that cured ulcers. He thinks, like undoubting Thomas, that magic is real, and is due to demons. Dreams sometimes foretell events. In corporeal matters “the stars are in truth rulers of the world”; the conjunctions of the planets probably explain “great accidents and great prodigies”; and comets may signify wars and the death of kings. “There is in man a double spring of action—nature, and the will; the nature is ruled by the stars, the will is free; but unless the will resists it is swept along by nature.” He believes that competent astrologers may in considerable measure prophesy the events of a man’s life, or the issue of an enterprise, from the position of the stars. He accepts, with certain reserves, the alchemic (today the nuclear physicist) theory of the transmutation of elements.92

His best scientific work was in botany. He was the first botanist since Theophrastus (so far as we know) to consider plants for their own sake instead of for their use in agriculture or medicine. He classified plants, described their color, odor, parts, and fruit, studied their feeling, sleep, sex, and germination, and ventured an essay on husbandry. Humboldt was surprised to find in Albert’s De vegetabilibus “exceedingly acute remarks on the organic structure and physiology of plants.”93 His enormous work De animalibusis largely a paraphrase of Aristotle, but here, too, we find original observation. Albert tells of “sailing the North Sea for the sake of research [experimenti causa], and landing on islands and sandy shores to collect” objects for study.94 He compared similar organs in animals and man.95

From the vantage point of our hindsight these works contain many mistakes; viewed against the intellectual background of their time they are among the major achievements of the medieval mind. Albert was recognized in his own lifetime as the greatest teacher of his age, and he lived long enough to be quoted as an authority by men like Peter of Spain and Vincent of Beauvais, who both died before him. He could not rival Averroës or Maimonides or Thomas in keenness of judgment or philosophic grasp; but he was the greatest naturalist of his time.

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