and it does not appear that he turned his attention again to globe making.85
The thirteenth century furnishes us with the names of two distinguished princes who were especially active in advancing scientific studies of their times. One of these was the Hohenstaufen Frederick II, concerning whom we are informed that he directed a learned Arabian, who sojourned at his court, to construct for him a celestial globe of gold on which the stars were to be represented by pearls.86 We are further told that as an outcome of his friendly relations with the rulers of the East, the Sultan of Egypt sent to him an astronomical tent of wonderful construction. In this the sun and the moon were represented and by means of a skilfully constructed mechanism they were made to rise and set, marking out the hours of day and night.87
As a ruler of like intellectual and scientific interests, the Castilian, Alfonso X, who lived in the thirteenth century, known as “The Wise” and as “The Astronomer,” deserves to be especially mentioned. By his order an elaborate astronomical work was prepared, which holds a place of first importance among mediaeval productions of its character. In this work the construction of globes is discussed in a very detailed manner, mention being made of every feature regarded as belonging to a properly constructed celestial sphere. So significant are certain chapters of this work for the history of globes and of globe making that a free translation is here given of that part relating to materials of which globes may be constructed.88 “A sphere may be made of many materials,” says the author, “as of gold, or silver, or copper, or brass, or iron, or lead, or tin, or of a combination of these metals; or they may be made of stone, or clay, or wood. They may also be made of leather, of cloth, of parchment in many layers, and of many other materials which men employ when they wish to give an exhibition of their skill. Those, however, who have carefully considered these things, have decided that there is nothing more suitable than wood and for the following reasons. If the globe should be made of gold, only a very rich man would be able to possess it; furthermore it would be very heavy. If it should be made of thin sheets of gold it could be easily indented and would not long remain a perfect sphere. If it should be made small, that which was represented thereon would not appear distinct. The same thing may be said of silver, although it is a metal stronger than gold, as it is likewise harder, and therefore is not so easily indented. Copper is a metal harder than either silver or gold, but is so dry that it can not be easily fashioned into a globe, which should always be well made. Brass, which is like dark colored copper, may be more easily fashioned, because it is more malleable than copper, and is stronger than either gold or silver. If, however, a globe made of this material should be thin it might easily lose its shape, and if thick it would be very heavy. Of all metals, however, this is the one most suitable for use in making spheres, as it is the one most commonly employed. A globe of iron would be very difficult to make and would be very heavy, and since the rust would have to be removed from it very frequently, there would be much danger of destroying the figures. A globe of tin, if made of a thin sheet, could be easily indented, and would be very heavy if the sheet of which made were thick. Lead, if thin, would offer less resistance to injury than tin, and is a material much heavier. Furthermore, as lead is inclined to turn black, the figures and the stars represented on a globe of this material would soon become so discolored as to be no longer visible. There is no way by which it can be cleaned without wiping out the figures. Although the metal could be combined to form that material of which water jugs and buckets are made it would be so fragile as to break like glass. Clay, which is also used for the making of water jugs, mortars, and fountains, is not suitable for globes, because if thin it would break easily, and if thick it would be very heavy. Moreover this material when prepared must be baked in a kiln which fact renders it unsuitable for use in making spheres. A globe should not be made of stone, since if this were transparent the figures could not easily be seen, and such material would be very heavy. It would not be fitting to make so noble an object as a sphere of the material of which jars are made. Leather would not be suitable, though it might be fashioned into a permanent spherical shape. Such material shrinks in hot weather or when brought near a fire. Cloth would not be suitable, though it were made very strong, since heat would cause it to shrink, and moisture would cause it to lose its shape, and this same thing may be said of parchment. A sphere of wood is strong and is of reasonable weight and may be made in the manner which we shall set forth.” The original manuscript of this work is profusely illustrated, including representations of the figures of the several constellations (Fig. 20).
Fig. 20. The Constellation Taurus.
In the latter part of the thirteenth century the mathematician, Giovanni Campano, a native of Novara and it appears a particular friend and supporter of Pope Urban IV, won distinction for his scholarly attainments in the field of astronomy.89 In addition to his work, titled, ‘Teorica planetarum,’ wherein he comments on the subject of astronomy and geometry, and makes copious references to the Greek geometrician Euclid, whose works he had translated into Latin, he prepared a treatise which he called ‘Tractatis de sphera solida.’ In the prologue to this work, after noting that the number of astronomical instruments which have been constructed is large, he states that in the main they agree in their representation of the movements of the heavens, adding that as the heavens are spherical, spherical instruments are to be preferred. In his first chapter, after alluding to the astronomical instruments described by Ptolemy, he proceeds to treat of the composition of solid spheres, which he says may be made of metal, or better, of wood. He gives rules for making the same by the use of the lathe, and notes in conclusion it is well to make the sphere hollow in order to lighten the weight. In the following chapters he treats of the inscription of the circles of the sphere, of the construction of the several rings employed in the mounting, such as the horizon and the meridian circles, and gives consideration to the representation of the several constellations on the surface of the ball. In the second part of his treatise he gives instruction as to how to use the instrument in the solution of astronomical problems.
There appears to be only the slightest evidence that Campano was acquainted with the work of Alfonso. His presentation of the subject, in all probability, was altogether independent of a knowledge of the Alfonsian tables. It is interesting to observe that in the day when astrology was in great favor in the universities of Europe, Campano continued to be interested in genuine astronomical science.
Albertus Magnus, in his ‘Liber de coelo et mondo,’90 devotes an entire chapter to a theoretical consideration of gravitation, asserting that the earth is spherical (Spherica sive orbicularis necessario), and proceeds to a demonstration of the theory, in which he practically follows the arguments of Aristotle, that every particle of the earth away from the center is continually in movement seeking that center, the result being the formation of a spherical body. He advances further, as argument in proof of a spherical earth, that the shadow it casts in an eclipse of the moon is circular.
Sacrobosco (John of Holywood or Halifax) (fl. 1230),91 who was active in the first half of the thirteenth century, much of the time as professor of mathematics in the University of Paris, prepared a work bearing the title, ‘Tractatus de sphaera,’ being in part a summary of the ‘Almagest’ of Ptolemy. In this work the theory of a spherical earth is supported in much the same manner as was done by Campano. The ‘Tractatus’ proved to be one of the most important quasi scientific geographical and astronomical textbooks of the later middle ages, being frequently copied, and frequently printed after the invention of that art.92
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