Peter was convinced that a knowledge of astronomy and astrology was not only valuable but necessary in the practice of medicine. “Those who pursue medicine as they should and who industriously study the writings of their predecessors, these grant that this science of astronomy is not only useful but absolutely essential to medicine.”[2808] Peter cites Hippocrates and Haly in his support and advises the medical practitioner to look up the nativity of the patient, or, if this is impracticable, to address an interrogation on the case to an astrologer. By astronomy one can also foretell changes in the weather and regulate the treatment of the case accordingly. Diet and drink, purgatives and drugs, should all be administered with due regard to the constellations. Two Differentiae[2809] of the Conciliator discuss at length the theme of critical days and their relation to the phases of the moon, which planet, as Peter more than once explains, is assumed to represent the influence of all the others, while to it is especially delegated the control of generation and corruption. The doctor should therefore keep his eye especially upon the moon, a point further emphasized in the pseudo-Hippocratic treatise of astrological medicine which Peter is said to have translated. In still another chapter of the Conciliator[2810] the question at issue is whether blood-letting is preferable in the first or some other quarter of the moon. Surgeons, too, should not operate when the stars are unpropitious and should note the apportionment of the members of the human body among the signs of the zodiac. When the patient’s symptoms are ambiguous, the perplexed doctor may bridge the gap in his medical prognostication by recourse to astrology. This will tend to increase his reputation with his patients who will marvel at his power of prognostication. While thus discussing his tenth question, whether a doctor should know astronomy, Peter adds that astrology is useful in metaphysics as well as in medicine, giving as an example the fact that Aristotle appeals to astrologers at one point of his Metaphysics.

Peter more than once touches upon the influence of the stars upon the length of human life: in Difference 9, for example, where he is inquiring whether men lived longer in ancient times than in his own day; in Difference 21, where the point at issue is whether a temperate “complexion” is more conducive to longevity, and where he indulges in considerable detail about the control of the planets over the process of generation; and in Difference 113, where the question is whether there is any way of putting off natural death. According to the astrologers, one hundred and twenty years—the length of a greater solar year—was the natural term of life, a considerable reduction from the age of the patriarchs of the Old Testament, but much longer than most men lived in Peter’s time. He thinks that the people of India live longer because their climate is subject to Saturn. In Difference 26 Peter divides the life of man into seven ages under the seven planets.

It is clear from many passages in the Conciliator that Peter believes that much of a man’s life and character can be inferred from his horoscope. The geniture of a prince may involve the slaughter of vast multitudes in war, although their own horoscopes may not have definitely indicated this fate for them but only a certain inclination in that direction.[2811] Peter devotes considerable space and pains to the process of generation and the problem of measuring the time of nativity. He gives physiological explanations why twins, even before birth, are not under the same astrological influence and approvingly quotes the lines of Lucan:[2812]

In connection with the subdivision of judicial astrology known as revolutions Peter was especially interested in the motion of the eighth sphere of the fixed stars, concerning which we have seen he wrote a distinct treatise[2813] and of which he treats in both the Lucidator[2814] and Conciliator.[2815] Ptolemy had reckoned that the sphere of the fixed stars moved one degree in a hundred years and that consequently the eighth sphere made a complete revolution every 36,000 years. Albategni’s estimate was 23,760 years for a complete revolution or a motion of one degree in the course of sixty-six years. Peter’s own calculation was that one degree was accomplished in seventy years. He regarded this as a matter of great importance because of the vast changes which he believed the revolution of the eighth sphere brought about. Its influence could even change dry land into sea, as the story of the lost island of Atlantis showed. Peter mentions the doctrine of the magnus annus, held by “certain Stoics and Pythagoreans” that history would repeat itself as soon as the eighth sphere had accomplished a complete revolution. His own favorite theory, set forth three times in the aforesaid three works, was that when the heads of the equinoctial and tropical signs of the mobile zodiac come directly under the heads of the same signs of the immobile zodiac in the heaven of the fixed stars, then virtue from the First Cause passes in a more perfect manner through the mediate causes or heavens and men live longer and are stronger. For some five hundred years before and after the period of exact coincidence a golden age occurs, men of genius appear in large numbers, and the world tends to unite under one government. Such a period in Peter’s opinion was that of classical antiquity, when there were great rulers like Darius, Alexander, and Julius Caesar; great minds like Hippocrates, Plato, Aristotle, Stoics and Peripatetics, Euclid, Abrachys, Ptolemy, Galen, Cicero, and Vergil; and when both the Roman law and the Christian religion were promulgated. But then gradually, as the discrepancy between the mobile and immobile signs increases, all is changed to the contrary, human nature deteriorates, the span of life is shortened, monarchy is corrupted, faith and law are made light of, the people are oppressed, and true sages are rare indeed.

In a number of places in the Conciliator Peter discusses the subject of the effects of conjunctions of the planets. He states[2816] that very rarely at long intervals of time, when a greatest conjunction of Saturn and Jupiter occurs in the beginning of the sign of the ram, a well-balanced type of constitution[2817] is produced, but never more than a single specimen at one time. Such a man becomes “a prophet, introducing a new law or religion, and teaching sages and men.” Such a man, according to Isaac Amaraan, Avicenna, and Algazetes, is midway between angels and sages, and some say that Moses and Christ were such men. Peter also hints at a coincidence between the length of time that astrology teaches that such a perfectly proportioned physical constitution will last and the duration of Christ’s life. Champier included this passage in his list of Peter’s errors. Champier further attacked the astrological doctrine of great conjunctions and censured Peter for connecting Noah’s flood and the advent of Mohammed with them. In another passage[2818] concerning this same conjunction of Saturn and Jupiter in the first degree of Aries[2819] Peter asserted that it not only altered the strength of human nature and affected the length of life but produced new kingdoms and religions, as in the case of the respective advents of Moses, Nebuchadnezzar, Alexander the Great, Christ, and Mohammed.

This astrological interpretation of history Peter carries out in further detail. As he had divided man’s life into seven ages, so he distributed periods of history among the seven planets. Each presides in turn over human affairs for a period of 354 years and four lunar months, a term analogous to the number of days in the lunar year. When Mars governed the world, the flood occurred because of a greatest conjunction of the planets in the sign Pisces. Under the Moon’s supremacy happened the dispersion of tongues, overthrow of Sodom and Gomorrah, and escape of the children of Israel from Egypt. Peter also alludes to the less significant minor conjunctions which happen every twenty years, to the moderate ones which take place every 240 or 260 years, and to the effects following eclipses. A solar eclipse seventy years ago, he says, was followed by sterility of the soil, movements of phantasms and of good demons and bad demons, intercourse of incubi and succubi, a weakening of human nature and increase of avarice and cupidity.

The chronology of some of Peter’s astrological periods of history has been sharply criticized. Thus Lea remarks, “Even worse was his Averrhoistic indifference to religion manifested in the statement that the conjunction of Saturn and Jupiter in the head of Aries, which occurs every 960 years, causes change in the monarchies and religions of the world as appears in the advent of Moses, Nebuchadnezzar, Alexander the Great, Christ, and Mahomet—a speculation whose infidelity was even worse than its chronology.”[2820] The printed editions of the Conciliator which I have consulted also give the time as 960 years, but it would seem as if the figure must have been wrongly copied in or from the manuscripts, since in the Lucidator,[2821] which I have examined in manuscript, Peter shows acquaintance with different systems of chronology, stating, for example, that Ptolemy and Galen flourished under Antoninus Pius in the year 886 of the era of Nebuchadnezzar or in 141 A. D. Peter therefore would appear to have known perfectly well that no such period as 960 years had elapsed between the time of Nebuchadnezzar and Christ, to say nothing of Alexander and Christ. In another passage of the Conciliator,[2822] moreover, Peter explains that conjunctions may precede by many years the events which they signify and produce but which are long in the making. Thus the conjunction for the flood preceded it by 287 years and the conjunction connected with Mohammed came fifty years before him, as Albumasar and Alchabitius state. In his treatise on the eighth sphere Peter stated that his theory of its motion and influence holds good independently of the question whether the world is eternal, as all the philosophers except Plato held, or had a beginning and when that beginning was. He gives, however, a list of various estimates of the number of years since creation, such as Bede’s estimate of 5259; Abraham Judaeus’ of 5071; the Septuagint, 7270; Josephus, 5262; and so on up to the enormous figure of 1,474,346,290 years given by the Indians and Persians.[2823]

Peter believed not only that astrologers could predict the future with considerable assurance of success, but also that they could influence the future to suit themselves and perhaps change threatening misfortune into good fortune by applying to earthly objects the occult virtue of the heavenly bodies. The way to capture and store up such celestial influence is by means of images made by human art with due reference to the constellations. Of such astrological images Peter speaks frequently in the Conciliator.[2824] Physicians are advised to construct such images at the proper time when “the vivifying and health-exciting celestial light” will flow freely into them, as is illustrated by the astronomical images of Ptolemy, Thebith ben Chorat, and others. The figure of a scorpion made as the moon is leaving the sign of the scorpion cures that reptile’s bite.[2825] Human life can be prolonged by such images which add to the influx of astral force received at birth.[2826] On the other hand, Peter elsewhere states the theory that the impulse to construct an image was received at birth from the stars,[2827] and so does not really alter their influence. He usually, however, speaks as if the employment of images was a matter of choice. They are more often made by night than by day, so that the rays of the sun may not obscure and dissolve those of the other heavenly bodies.[2828] The astronomers of India employ allegorical images.[2829] Peter himself “has tested to remove pain in the intestines the figure of a lion impressed on gold when the sun was in mid-sky, with the heart of a lion, when Jupiter or Venus was in aspect and the evil unfortunate stars were declining.” He bound this amulet “on the bare flesh with a string made of sea calf’s hide and a clasp from the bone of a male whale.”[2830] What could be more magical? In another passage Peter notes that theologians attribute the efficacy of such images to demons, but he sets aside this suggestion as not in accord with his present method, which apparently takes into account only natural and not spiritual forces, although he suggests that the celestial light and force may be regarded as the instruments of intelligences.[2831] In the Lucidator Peter makes much the same distinction between astronomical and necromantic images as Albertus Magnus had made in the Speculum astronomiae. Notes by Peter on astrological images are contained in the Astrolabium planum, published in 1488.[2832]

Peter refers twice in the Conciliator[2833] to his success with an invocation to God to acquire knowledge, when the head of the dragon and Jupiter were together in mid-sky and the moon was approaching them. He also cites Albumasar in Sadam for a similar practice by “the kings of the Greeks,” when they wished to ask God for anything. Elsewhere[2834] he states that the defenders of fascination and incantations aver that their potency consists in the virtue which the soul of the operator receives from the stars, just as an image receives their motion and light. The horoscope of the person uttering the invocation is a factor of some importance, but not the preponderating influence.[2835] Not a few of the Magi invoke Jupiter, Saturn, or another heavenly body by the name of the intelligence which guides it.[2836]

This last passage and one or two others already cited show that Peter was inclined to associate spirits and intelligences with the heavenly bodies. Once he describes a celestial body as “perpetual and incorruptible, leading through all eternity a life most sufficient unto itself, nor ever growing old.” In the same chapter[2837] he tells us that when Aristotle wished to investigate the number of Intelligences, he betook himself to two famous astrologers and according to the number of spheres as stated by them calculated the number of Intelligences. In the preceding chapter[2838] he had repeated from Averroes the following association of seven intelligences or angels with the planets: Saturn and Cassiel, Jupiter and Sachiel, Mars and Samael, the Sun and Michael, Venus and Anael, Mercury and Raphael, the Moon and Gabriel.

This passage and Peter’s invocation are a dangerously close approach to astrological necromancy. Enough so perhaps to justify the reproach which Champier repeated from some “recent authority” that Peter borrowed a great deal from Picatrix, “a very idle book full of superstitious prayers to planets and evil spirits.” Champier, however, cited no specific passages to substantiate this charge, and I doubt if it can be shown that the Conciliator either cites or makes unacknowledged quotation from Picatrix. It will also be observed that Peter does not assert that the stars themselves are spirits or intelligences or gods, and that both Aquinas and Albert were inclined to agree that angels or heavenly intelligences moved the stars. That Peter’s views were objectionable to some persons, however, is indicated by the closing passage of this ninth Differentia, in which he has associated seven spirits with the planets, the rise of prophets and new religions with great conjunctions, and activity of demons with solar eclipses. Some malicious persons have long troubled him, he says, but his utterances in nothing derogate from divine wisdom but rather confirm it, and at last an apostolic mandate has snatched him and his truth from the hands of his detractors. In other words, the pope has protected him. Peter’s astrology sometimes seems to show scant regard for human free will, but he recognized it as an essential Christian doctrine.[2839]

Peter alludes several times[2840] to the subject of fascination in connection with images and incantations. It seems evident that he is here trying to account among other things for hypnotic power. In the Lucidator he defines maleficium, the usual word for sorcery, as a sort of fascination, “taking possession of one’s powers so that one loses self-control,” and “impeding sexual intercourse.”[2841] In opposing the theory that vision is by extramission of rays Peter explains the deadly glance of the basilisk as due to corrupting vapor and not to visual rays, and fascination as caused by some more occult force than the evil eye in a literal sense.[2842] And when arguing that the confidence of the patient in the doctor is a factor in the cure Peter emphasizes the power of a strong will impressed in an occult fashion.[2843] Some men, it is true, like the followers of Asclepius, deny any virtue of the mind and regard their fellow-men as swayed like beasts by the passions of the senses, deeming wisdom, sobriety and continence a jest, calling human affection and altruism into question, and further despising dreams, divinations, prudent counsels and the whole subject of astrology. But Peter believes in the power of one mind over another or over matter. Such a mind can cure the sick or even cast a man into a well or cause a camel to enter a Turkish bath (caldarium). It is also one of the causes of prophetic power. The believers in fascination and incantations say that such marvelous virtues of the mind are derived from the stars. But Christians regard prophetic power as directly inspired by God, an opinion which seems ridiculous to the Peripatetics.

In much the same way Peter discusses incantations.[2844] He lists several definitions of an incantation, such as that ascribed to Socrates, “words deceiving human minds,” or “an utterance put forth with astounding influence in aid of an enchanted person who is especially confiding,” or “an utterance at discretion of meaningless words, which since it has to do with the strange and occult is esteemed the more by the person enchanted and so helps him the more.” An incantation may be either spoken, or written and bound on the body. The enchanter should be astute, credulous, and strong-willed; the person enchanted should be eager, hopeful, and disposed in every way to forward the success of the operation. Incantations are especially effective in sleep or in the case of women and simple folk who have the more faith in them. Peter tells an amusing anecdote of a noble who taught a poor old woman to repeat as an incantation the sentence, “Two and three make five and so do three and two.” He thought her a witch, however, and when a fish bone stuck fast in his throat, sent for her to remove it. When he found that she really knew no magic except the absurd incantation which he had himself taught her, he laughed so heartily that the bone was dislodged and he was thus cured by his own incantation after all.

All this sounds rather sceptical on Peter’s part, and he also recalls Galen’s detestation of certain medical authors who wrote down superstitious words and fables such as old-wives and witches are wont to repeat and stupid gypsies who utter fascinations. “For they conjured and sprinkled and suffumigated medicines as if divine, when they plucked the herbs from the soil or when they suspended them about the neck or elsewhere like a phylactery, all which is false and stupid and offensive to the art of medicine.” But while Peter joins in condemnation of such superstitious medicine, he yet believes in the efficacy of incantations and represents their opponents as incredulous and materialistic persons who will accept only action by gross material contact. He admits that there is no property in the incantation itself nor in its sound when uttered to explain its marvelous effects. We must look rather to the virtue of the mind of the person repeating the charm, to faith on the part of the person to be benefited, and to divine, angelic, demonic, or sidereal assistance. At any rate experience demonstrates the validity of incantations and spoken words, as in the case of the Eucharist, or of the divine names employed in the notory art, or the restoration to life of a dead man which was performed in Peter’s presence by magic words which the enchanter uttered in the ear of the corpse. Peter goes on to speak of the movement of the holy wafer or Psalter or sieve towards a thief who enters a church. Other wonders wrought by incantations which he lists are the ability to endure torture without giving signs of pain or to walk over sharp swords and hot coals without injury, to lift another man or raise a great weight with a single finger, to stupefy snakes and tame wild horses, cause insomnia, reveal the future, painlessly extract arrows that are so deeply embedded in the bone that they could not be pulled out. Paroxysms of epilepsy may be quieted by pronouncing the names of the three Magi in the patient’s ear. Peter also repeats the cure for epilepsy found in so many medieval authors and involving religious ceremonial and repetition of a verse from the Bible. Anent Peter’s allusion to the employment of divine names in the notory art, we may note that a work on that subject is listed among evil books in his Lucidator.[2845]

The superstitious esteem for certain numbers which prevailed both in ancient and medieval times does not pass unnoticed in the Conciliator. Arguing the question whether the child born in the eighth month will live,[2846] Peter discusses the subject of perfect and imperfect numbers for three columns, stating that this is the doctrine of Pythagoras and of arithmeticians in general. In a later chapter,[2847] however, he declares that natural phenomena cannot be proved by arithmetical numbers since they are not caused by them, and alludes to Aristotle’s strictures upon Pythagoras.

Poisoning and magic were often scarcely distinguished in antiquity. The Greek word φάρμακον and the Latin veneficium or veneficus might have reference either to poisoning or sorcery, either to a poisoner or enchanter. Plato states in his Laws[2848] that there are two kinds of poison employed by men which cannot be clearly distinguished, although one variety injures the body “according to natural law,” while the other “persuades overbold men that they can work injury by sorceries and incantations.” The Latin poet Lucan centuries later drew a sharper distinction when he declared, “The mind which is enchanted perishes without foul trace of poisoned draught,” and this dictum we have found embodied in more than one medieval definition and description of magic. However, all magic is not enchantment; the poisoner and magician worked in the same secret and sinister style, sought similar injurious ends, and availed themselves of the same powerful occult virtues in natural objects. Poisoning and bewitching seemed very similar processes, especially at a time when men believed in the existence of poisons which could act at a distance or after a long interval of time. In one passage of the Conciliator[2849] Peter uses the word veneficus rather in the sense of an enchanter or magician than a poisoner, when he says that, if you wish to injure another person or to make him love you, the venefici direct you to gaze fixedly at him at the same time uttering a certain incantation. But let us now turn to the treatise De venenis, in which Peter has much more to say on the subject of poisons.

It will be recalled that Peter’s treatise on poisons was written for the pope. The topics considered in its six main chapters are: the classification of poisons, how they act upon the body, how to guard against them, the effects and cures of a long list of particular poisons, and finally the problem of a panacea or bezoar against all poisons. Peter classifies poisons according as they come from animals, vegetables, or minerals, and as they take effect internally or externally. Those which take effect internally are usually administered in food or drink, or swallowed without admixture. But one may be poisoned externally not only by contact, as in the case of snake-bite, but through the sense of sight, as when the glance of the basilisk kills, and through the sense of hearing, as when the regulus[2850] kills bird or beast by its hiss. In fact, poisoning may be through any one of the five senses. Some snake-bites Peter classifies under the sense of taste rather than touch. Other serpents emit a poisonous odor, or kill a person who touches them only with the tip of a long lance. The hands and arms of fishermen become paralyzed when they take hold of nets in which a certain fish has become entangled. These last are perhaps exaggerated accounts based upon electrical shock.

Poisons may also be classified according to the form of their species (forma specifica). Some prove fatal owing to the excessive preponderance of one quality, being excessively hot or cold or moist or dry. Others are deadly because their entire composition, the very form of their species, is fatal. Peter then gives an interesting definition of this “specific form.” “It is nothing else than the value or valence (meritum) which any object composed of the four elements acquires from the proportions of those elements existing in this compound and from the influence of the fixed stars which regard the species of inferior compounds.” Through the light of the stars streaming down in straight lines pyramids of astral force concentrate upon terrestrial objects,—the same doctrine of stellar rays, emanation, and multiplication of species that we have met already in Alkindi, Grosseteste, and Roger Bacon. Peter adds that this specific form of any compound is not easy to discover except as human experience gradually reveals it empirically, “because we do not know and we never shall know the quantities and the weights of the elements in the compounds.” That is to say, Peter sees the desirability but despairs of the possibility of any such discovery as that of atomic weights and valences, and consequently of a true science of chemistry. His despair is not surprising in view of the fact that medieval men were still trying to conduct their scientific researches upon the outworn Greek hypothesis of only four elements, earth, air, fire, and water, all of which are really compounds and indeed in the middle ages were not supposed to be ever found in their pure state. Desperation like Peter’s was needed before science could be induced to take a fresh start, and, like Arnald of Villanova, he is to be given credit for an approach to the chemical conception of valence.

With the subject of alchemy, it may be remarked in passing, Peter appears to have had little to do, and not even any spurious treatises on the subject are extant under his name, as they are in the cases of Albertus Magnus, Thomas Aquinas, Roger Bacon, Arnald of Villanova, and Raymond Lull. Colle,[2851] however, noted a passage in the Conciliator[2852] where Peter speaks of two friends of his who had told him that they had succeeded “by the art of decoction” in making silver which was true to every examination but from which they had not profited much openly.

In his second chapter Peter discusses various mineral, vegetable, and animal poisons under the caption, “Of each poison in particular” (De unoquoque veneno in speciali). Quicksilver made by the art of alchemy he declares a more deadly poison than natural mercury. He is either an early advocate of inoculation and homeopathy, or else is guilty of silly reasoning based upon sympathetic magic, when he states that the magnet taken internally produces melancholy and lunacy and that doctors employ it with other medicines to cure melancholy. Incidentally he mentions two kinds of magnet, one which attracts iron toward the north pole, another which draws human flesh toward the south pole. Vegetable poisons may be the juices of herbs, the fruit of trees, or seeds. Some animals have poison in their brains; some, in their tails; some, in the blood; some, in the saliva and spittle; some, in the gall; and some, in their entire bodies.

The question, how poison takes effect upon the human body, occasions Peter considerable difficulty, since he is unwilling to admit either that the heart naturally attracts poison or that poison runs naturally to the heart. Avicenna says that a man with a hot heart offers the best resistance to poison, but Peter adds that much depends upon the human soul and the constellations. He notes that the action of poison is very similar to that of medicine and thinks that the art of medicine was suggested by the action of poisons. Incidentally he repeats from his authorities statements that there are trees whose shade is poisonous to sleep in or to bathe beneath, and that a man was killed by the vapor from wood cut near the caverns of serpents which was used as fuel in heating his bath. He also repeats the tale of Socrates and the dragon.[2853]

The fourth chapter is concerned with safeguards against poison, which often take the form of amulets and charms and are, if anything, even closer akin to magic than the poisons themselves. There are the horns of a serpent which sweat at the advent of certain poisons but not of others. There is the gem that ceases to gleam in the presence of poison. There is the stone which Alexander wore in his belt until a jealous snake stole it while he was bathing in the Euphrates. There is the following image recommended in the book of the Persian kings—possibly the Kiranides. Engrave the gem Ematites with a kneeling man girded by a serpent whose head he holds in his right hand and tail in the left.[2854] Set this stone in a gold ring and under the gem place a dried root of serpentaria. Either Peter or the author of the book of the Persian kings affirms that he wears such a ring and has been preserved from poisoning by it. An emerald is another good safeguard against poison. Peter perhaps has a confused recollection of a story told by Albertus Magnus[2855] when he adds that it has been proved that a toad’s eyes will crack if it gazes at an emerald. There are seven herbs, namely: Ipericon, “which Achilles is said to have found in the Trojan army by the oracle of Apollo,” Vincetoxicum, Enula, Rafanus, Diptamus, Aristologia, and Lactucella, which will cure any poison. This virtue is not due to the elements composing them but to the force of the seven planets. Peter’s antidotes are not all occult or talismanic. He also prescribes the more commonplace methods of a drink of butter and hot water to provoke vomiting, the use of a syringe to clear the intestines, the application of a relay of hot fowls to the wound, or the sucking of it “by the mouth of some slave or servant”—sclavi vel servi, an interesting bit of etymological evidence of the medieval transition from the Latin servus to the modern word “slave,” and for the derivation of the latter from the Slavs who were sold in southern and western Europe. Peter also mentions the famous terra sigillata which, he says, causes vomiting if there is any poison in the stomach. Kings and princes in the west[2856] take it with their meals as a safeguard, and it is called terra sigillata because stamped with the king’s seal. Now, however, the seals are no longer trustworthy and Peter cautions the pope against what may be offered him as terra sigillata.[2857] Over seventy brief chapters are next devoted to enumeration of the effects produced by as many poisons and how to remedy them. The poisons include the blood of a rubicund, choleric man, the bite of a fasting man, the gall of a leopard, and the salamander. Among the remedies are duck’s fat and pulverized mouse dung. The remedies operate against the poison either by “breaking its sharpness,” or “resolving its substance,” or “expelling it,” or “corrupting it and utterly taking away its virtue.”

Finally Peter comes to the discussion of “bezoartic virtues” which free from death by occult and divine virtue rather than by their natural composition. Under this head he proposes to deal with two difficult questions: first, whether theriac is a bezoar (i. e., antidote or panacea) and medicine for every poison; second, whether there is any poison which can be set to act at a given time, so that the victim will die from it then and not before. In those copies of the De venenis which I have seen the discussion of this second question is never reached. Perhaps it was intended only for the pope’s ear and not published. As for the former question, some believe in a bezoar or stone that frees from all poisons without medical assistance. Edward I of England, when wounded by the Sultan’s poisoned sword, is said to have been cured by such a stone which “the general preceptor of the Temple gave him, and I have seen one like it.” It is red, purulent, light as a sponge, and fragile as gypsum. But Peter inclines to believe that each poison has its own antidote which is the best cure for it. Like Galen, however, he extols that “divine and noble” artificial compound, theriac, a mixture of all the single medicines which break or dissolve or expel poisons. It may, he thinks, deservedly be called Bezoar, since it is good against all poisons, although for any particular poison there may be a superior particular remedy. After Peter’s treatise has apparently ended with the words, Deo gratias, there is added a note from the Pandects concerning the stone Begaar or Bezoar, asserting its reality and superiority to any simple antidote or any of the compound theriacs.[2858]

Peter’s treatise on physiognomy mentions Philemon, Aristotle, Palemon, and Loxius as the founders of the art, and Rasis, Zacharias, and Avicenna as Arabian authorities. Peter proposes to combine their separate contributions to the subject “into one lucid and perfect doctrine.” The first draft intended for the captain-general of Mantua has got into “the hands of some rascal who scorns to communicate it to me or others.” At the sollicitation of his friends and lest invidious detractors envying another’s work gain glory from it, Peter has written another draft which he flatters himself is longer and better. “So praise be,” he piously ejaculates, “to God, the better producer of everything, who from that evil has created this good and best!” Peter’s treatise differs from other Physiognomies mainly in its emphasis upon astrology, to which its third book is largely devoted. He gives the influence of each sign and planet upon the physique and character of the person born under it, and discusses in considerable detail the process of generation, the influence of heredity as well as of the stars, and the effect upon the babe of any strong imagination, especially on the part of the mother, during the period of generation.

Peter’s penchant for astrology is further evidenced by his Latin version of the various astrological treatises of Abraham Aben Ezra, and his translation of the brief treatise attributed to Hippocrates on the prognostication of diseases according to the moon. Peter or some previous translator or editor opens it by saying that while reading the works of Hippocrates he found this book, “small but of great utility and very essential to all physicians. Whoever is well acquainted with it can pronounce health, death, or life in every infirmity.” Peter brings in astrology even in his commentary on the Problems of Aristotle. When Aristotle mentions an astronomer or astrologer in a derogatory manner in the same breath with a juggler or mime or pipe-player or rhetorician, Peter is at pains to explain that in Aristotle’s time the science of judicial astrology had not yet attained its present perfection.

In those of his works which are certainly genuine Peter seldom uses the word “magic” and never, I think, speaks of it approvingly, although Michael Savonarola could see no reason why he should not do so. Despite his reputation for magic, the longest discussion of such arts in his admittedly genuine works occurs in the Lucidator,[2859] where, after the manner of Michael Scot and Albert in the Speculum astronomiae, he is chiefly concerned to distinguish astrology favorably from these other forms of divination and magic. With occasionally some additional detail he mainly repeats the old account of the origin of magic with Zoroaster or Cham, the son of Noah, and with Hermes or Enoch or Mercurius; and the old classification of the occult arts found in Isidore and Hugo of St. Victor.

Naudé states, on the authority of Castellan, that when Peter was burned in effigy after his death, the reading was forbidden of three superstitious and abominable books which he had composed, entitled respectively, Heptameron, Elucidarium Necromanticum, and Liber experimentorum mirabilium de annulis secundum 28 mansiones lunae (Book of marvelous experiments with rings according to the twenty-eight mansions of the moon).[2860] Naudé adds, however, that Trithemius and Symphorien Champier could find no books on magic by Peter of Abano.[2861] Such treatises, however, exist both in print and in manuscripts, which last are mainly of late date, and will be found listed in Appendix II. Prophecies ascribed to “the most reverend nigromancer, Peter of Abano,” were printed in Bologna in Italian about 1495 and occur also in Latin in a Vatican manuscript. The printed Heptameron or Elements of Magic consists entirely of specific directions how to invoke demons, and if genuine, might account for Champier’s charge that Peter borrowed from Picatrix. The reader is instructed in the construction of the magic circle, in the names of the angels, and concerning benedictions, fumigations, exorcisms, prayers to God, visions, apparitions, and conjurations for each day of the week. The work seems quite certainly spurious.