§27. Doctor Mirabilis
Roger Bacon has been described as the scholar “who most thoroughly grasped, and most elaborately developed Grosseteste’s attitude toward nature and the theory of science.” Like Grosseteste he urged Christians to catch up with “the philosophers,” that is, Greeks and Arabs.
He wanted not synthesis but advancement, starting where the Greeks arrived in natural philosophy and surpassing them. The newly available works of Aristotle may have provoked his enthusiasm for natural philosophy, but the expectation of innovation is not something he learned in Aristotle.Bacon studied at Oxford about a generation after Grosseteste. Later he was in Paris, where he was one of the first to lecture on Aristotle, and did so more often (he said) than any other master. It was probably during this Paris sojourn that he met the man (then a cardinal) who later become Pope Clement IV, and Bacon's patron. He returned to Oxford in the mid-thirteenth century, entered the Franciscan order, and began experimental research. Then he is in Paris again, where he composes his Opus majus in response to a commission from the new pope, Clement IV, who asked Bacon to explain the value of natural philosophy for theology. Some years later Bacon fell under suspicion in his order and was briefly imprisoned. Despite rampant speculation, the cause is unknown. Bacon has been a magnet for legend ever since the fourteenth century—magician, alchemist, English Galileo, martyr to science—but there is no evidence of his supposed crime.27
Bacon understood Aristotle's natural philosophy as well as anyone in Europe at the time, but he also sees faults and opportunities for advance. His Opus majus offered the pope an Aristotle copiously supplemented with material from Pliny, Seneca, and Arabic natural philosophy. He makes an unprecedented plea for combining mathematics with experiments.
The urgency of experiments is palpable in his writing. Their value was impressed on him by Petrus of Maricourt, also known as Petrus Peregrinus, and his Epistola de magnete (1269). Little is known of Petrus, who might have been noble, perhaps trained as a military engineer, and may have traveled to the Orient as a pilgrim or crusader (hence Peregrinus). His Letter was continuously studied in manuscripts until its first printing in 1558, and the work remained the summa of research on magnets until it was superseded by William Gilbert's De magnete in 1600.28Associated with magic and inspiring fantastic stories, magnetism was the medieval scholar's best example of something wondrous. Against that current of expectation, Petrus's Epistola is the best example of experimental inquiry in the thirteenth century. The treatise describes, in an objective and exact manner, all the basic magnetic phenomena, including the distinction of poles, polar attraction and repulsion, magnetic induction, and application in the compass, all of which are illustrated with systematic experiments the author must have actually performed. Consider his words from the introduction:
You must realize, dearest friend, that while the investigator in this subject must understand nature and not be ignorant of the celestial motions, he must also be very diligent in the use of his own hands, so that through the operation of this stone he may show wonderful effects. For by his industry he will in a short time be able to correct an error which he would never do in eternity by his knowledge of natural philosophy and mathematics alone, if he lacked carefulness with his hands. For in investigating the unknown we greatly need manual skill, without which we can usually accomplish nothing perfectly. Yet there are many things subject to the rule of reason which we cannot completely investigate by the hand.29
For Bacon, Petrus is the “master ofexperiments” (dominus experimentorum), about whom he writes, “Of discourses and battles of words he takes no heed...
he is a master of experiment. Through experiment he gains knowledge of natural things, medical, chemical, and indeed of everything in the heavens or [on] earth. He is ashamed that things should be known to laymen, old women, soldiers, ploughmen, of which he is ignorant.” The urgency Bacon expresses for mathematics in natural philosophy is not something he learned in Aristotle, who encourages no such expectation. For Bacon, mathematics is the key to all science. Experiments are no less necessary, however, which is the lesson he takes from Petrus. “Reasoning does not prove anything, everything depends on experience.” Reasoning draws conclusions, but its proofs lack weight until they are confirmed by experience. However logical the argument, the mind wavers, but experience settles all doubt. This was Galen’s principle too, as it will be Galileo’s.30The expression scientia experimentalis first appears in Latin literature in Bacon’s Opus majus. He explains three prerogatives of experimental science. One is to investigate and confirm by experiment the notable conclusions of all the other sciences. Experiments engender the last degree of certainty for demonstrations, and can demonstrate the otherwise non-demonstrable starting points of the sciences. Second, experiments go beyond what a science on Aristotle’s model establishes even in its own domain. Bacon gives three examples, the first being the invention of astronomical instruments like the astrolabe. The second is knowledge useful for the prolongation of life. The cause of life’s shortness is accidental and therefore a remedy is possible, yet medicine supplies only rules of health; it will take experiments to discover the secret of indefinite prolongation. These experiments should continue the work of the Arab alchemists because the same substance that allows the alchemist to produce all the gold he wants also prolongs life. “For that medicine which would remove all the impurities and corruptions of a baser metal, so that it should become silver and purest gold, is thought by scientists to be able to remove the corruptions of the human body to such an extent that it would prolong life for many ages.”31
The third prerogative of experiments is to penetrate secrets inaccessible to other forms of inquiry.
Bacon promises the pope “knowledge of the future, of the past, and the present,” as well as “wonderful works by which [this knowledge] excels the ordinary astronomy in the power of making judgments [based on the stars].... This science has discovered the definitions and the means by which it can answer easily every question.” This enhanced astrology is one example of how Bacon expects experiments properly conducted to reveal undreamed of powers in nature. He looks to a new experimental logic to sort out the good and the bad in magic and divination, as Aristotle’s logic enabled scholars to sort out good and bad arguments. An experimental science “knows how to test perfectly what can be done by nature, what by the effort of art, [and] what by trickery, [knowing] what the incantations, conjurations, invocations, deprecations, [and] sacrifices that belong to magic mean and dream of, and what is in them, so that all falsity may be removed and the truth alone of art and nature may be retained.”32The pope asked Bacon to explain what natural philosophy contributes to theology. Bacon replies that this experimental science “is useful not only to philosophy, but to the knowledge of God, and for the direction of the whole world.” He promises technology capable of altering the environment of a whole region, and thereby altering by design the habits of the people who live there. Whole armies can be roused to desire or aversion at will. Other technologies foreseen include an ever-burning lamp and the wonderful secret of gunpowder, whose first European formula Bacon hid in a cipher at the conclusion of his Letter Concerning the Marvelous Power of Art. His patron should expect instruments to destroy the enemies of the faith. These enemies “should be destroyed rather by the discoveries of science than by the warlike arms of combatants.” He warns that the Antichrist will use these means freely and effectively to crush and confound the power of this world, but that this imminent peril “would be easy to meet if prelates and princes promoted study and investigated the secrets of nature and of art.”33
I mentioned that it is difficult to think about experiments without doing some.
Bacon’s experimental observations established that the maximum altitude of the rainbow’s bow, reached when the sun is on the horizon, is forty- two degrees. A modern authority considers Bacon’s De speculis comburentibus to contain “possibly the most incisive and original piece of geometrical optics produced in the West during the entire middle ages.” Nobody in Europe, or any available Greek or Arabic source, had investigated light’s modes of propagation as deeply as Bacon did. Yet medieval natural philosophers could show strange indifference to blatant misstatements of fact based on imaginary experiences copied from earlier writers, and which critical inspection might easily correct. Roger Bacon was no exception, which is inconvenient for those who want to make him a martyr to science. “No one likes to see a hero of scientific progress proposing to prolong human life with the aid of a potion containing specially prepared dragon-flesh.”34