Our discussion of Grosseteste will be based upon some treatises included in Baur’s edition of his philosophical works. They are mostly brief and in some cases seem rather fragmentary. We shall not be concerned with his Greek grammar or with his theological writings, which occupy half of the bibliography in Pegge’s Life.[1427] His letters contain some hints of his scientific works but nothing bearing on magic or astrology. It used to be stated that Grosseteste certainly constructed charms to expel maladies, that he invented forms of words to exorcise fiends, and that he worked cures by engraved gems.[1428] The ascription to Grosseteste of treatises on Necromancy and Sorcery, and the Philosopher’s Stone, is, however, false and grew, Baur says, from marginal glosses appended to one of his genuine works.[1429] What we shall note in Grosseteste’s works will be mainly his attitude to experimental science on the one hand and to astrology on the other.
Scientific writings little affected by his ecclesiastical position.
In these scientific treatises by Grosseteste there is little to suggest the Christian bishop. However, in the work “On the Fixity of Motion and Time” he opposes the Aristotelian doctrine that the universe or motion of the celestial bodies is eternal.[1430] And in a second treatise, “On the Order of the Emanation of Things Caused from God,” he expresses the wish that men would cease to question the scriptural account of the age and beginning of the world.[1431] A third treatise “On Freedom of the Will” also lies on the frontier of philosophy and theology.
Reliance on experience.
Grosseteste affords us further examples in a number of passages of that reliance upon experience and reason, that rejection of certain views as contrary to experience, and yet that acceptance of statements in old authors as based upon experience, which we saw in Galen and William of Auvergne’s “experimental books,” and shall see in Albertus Magnus and the other medieval scientists. Grosseteste speaks, however, not merely of experience or experimenta, but also of experimenters (experimentatores).[1432] We may first note some use of observation and experience in astronomy and geography. In his treatise on comets he alludes to “experience in natural things.”[1433] In his treatise on the Sphere[1434] Bishop Robert declares that the sphericity of the earth and of all the stars and planets “is shown both by natural reasons and astronomical experiences,” that is, in the case of the earth, by the observations of the sky by men in different parts of the earth. In the same work he says that Thabit ben Corra (836-901 A. D.) working over the operations of Ptolemy, “found by certain experiments that the motion of the fixed stars was different.”[1435] Likewise in his treatise On the Generation of the Stars Grosseteste remarks of one contention that “experience shows the contrary” and of another view that it “is against both experience and reason.”[1436] Again in writing Of the Nature of Places he adduces in support of his positions “experiments and reasons,” and “divers authors and experimenters.”[1437] The old legend of the Hyperboreans who dwell among mountains near the pole in such a salubrious and temperate climate that they live on and on until they tire of life and commit voluntary suicide by leaping off cliffs into the sea, Grosseteste introduces by the statement: “It has also been found by experience, as authors tell”—among whom he names Pliny, Solinus, and “Marcianus in his geometry.”
Theory of vision and science of perspective.
In the realm of physics Grosseteste not only mentions experience in discussing vision and what he calls Perspective but also brings to our notice a recent or approaching experimental discovery, that of magnifying lenses. In his treatise on the rainbow he makes a rather unpromising beginning. After arguing whether the sense of sight operates by the eye receiving something within itself, as natural philosophers are prone to hold, or by sending forth a visual species or rays, he decides as was usual with men of his time in favor of the latter alternative.[1438] He cites Aristotle in his last book on animals as saying that a man with deep-set eyes sees farther because his visual virtue is not spread or scattered but goes straight—as if from a long-barreled gun—to the things seen.
Experimental discovery of lenses.
Grosseteste then goes on to say that there are three parts of Perspective. The first is that concerning the sight with which he has just been dealing. The second concerns mirrors. The third has been “untouched and unknown among us until the present time. Yet we know that Aristotle completed this third part”—he of course did nothing of the sort—“and that it is much more difficult in its subtlety and far more wonderful in its profound knowledge of natures than the other parts. For this branch of Perspective thoroughly known shows us how to make things very far off seem very close at hand and how to make large objects which are near seem tiny and how to make distant objects appear as large as we choose, so that it is possible for us to read the smallest letters at an incredible distance, or to count sand or grain or grass or any other minute objects.”[1439] So far the passage reads as if it might be merely the exaggerated dream of fancy. But Grosseteste proceeds to state “how these marvels happen,” which seems to be by the breaking up of “the visual ray”—or as we should say, by the refraction of rays of light—as it passes through several transparent objects or lenses of varying nature. He explains also that great distance does not make an object invisible but the narrowness of the angle under which it is seen.[1440] This he proceeds to illustrate “by experiments” (per experimenta). Again in his treatise on comets he mentions “those who have experienced that by a transparent figure interposed between the spectator and the object seen it is possible that the thing seen should be multiplied and that great things seem small and conversely according to the shape given the interposed transparent object.”[1441] I have given as far as possible a literal translation of Grosseteste’s words on this point in order to convey his exact or inexact meaning. If these passages are not a sufficient proof that magnifying lenses of some sort were already discovered, they at least point the way to the microscope and telescope, and we know that eye-glasses for nearsightedness were in use at the latest by the end of the thirteenth century.
Mentioned also in The Romance of the Rose.