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). [Illustration: 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.