The name of Bernard Silvester is persistently associated in the manuscripts with a work bearing the title _Experimentarius_, which seems to consist of sets of geomantic tables translated from the Arabic. Its prologue is unmistakable, but it is less easy to make out what text should go with it and how the text should be arranged. Sometimes the prologue is found alone in the manuscripts,[296] and the text which accompanies it in others varies in amount and sometimes is more or less mixed up with other similar modes of divination. The prologue is sometimes headed, _Evidencia operis subsequentis_, and regularly subdivides into three brief sections. The first, opening with the words, _Materia huius libelli_, describes the subject-matter of the text as “the effect and efficacy of the moon and other planets and of the constellations, which they exert upon inferior things.” The writer’s opinion is that God permits mortals who make sane and sober inquiry to learn by subtle consideration of the constellations many things concerning the future and persons who are absent, and that astrology also gives information concerning human character, health and sickness, prosperity, fertility of the soil, the state of sea and air, business matters and journeys. In a second paragraph, opening, _Utilitas autem huius libelli_, the writer states that the use of his book is that one may avoid the perils of which the stars give warning by penitence and prayers and vows to God who, as the astrologer Albumasar admits, controls the stars. And through them the Creator reveals his will, as in the case of the three Magi who learned from a star that a great prophet had been born. Finally, in a paragraph of a single sentence, which opens with the words, _Titulus vero talis est_, we are informed that the title is the _Experimentarius_ of Bernard Silvester, “not because he was the original author but the faithful translator from Arabic into Latin.” [Sidenote: Pictures of Bernard Silvester.] In one manuscript which contains the _Experimentarius_ there is twice depicted, although the second time in different colors, a seated human figure evidently intended to represent Bernard Silvester. He is bearded and sits in a chair writing, with a pen in one hand and a knife or scalpel in the other. Neither miniature is in juxtaposition to the prologue in which Bernard is named, but in both cases the figure is accompanied by five lines of text, written alternately in red and blue colors and proclaiming that Bernard Silvester is the translator and that the number seven is the basis in this infallible book of lot-casting.[297] It would not be safe, however, to accept this miniature as an accurate representation of Bernard, since the manuscript is not contemporary and it contains similar portraits of Socrates and Plato, Pythagoras, Anaxagoras, and Cicero. [Sidenote: Problem of a spying-tube and Hermann’s relation to the _Experimentarius_.]