As a compass was often set into the horizon circle so also we frequently find a large or small compass set into that plate which in certain globes was employed as a support, tying together, as it were, the lower extremities of the base columns.[208] It will have been noted that the globes referred to in the preceding pages varied greatly as to size, from the small ball representing the earth, and but a few centimeters in diameter, to be found in the center of those armillary spheres representing the Ptolemaic geocentric system, to the great globe of Coronelli fifteen feet in diameter constructed for Louis XIV of France. With rare exceptions metal globes were made small in size. Those globe balls or spheres, in the construction of which a mould was employed, usually had a diameter under 50 cm., although we find some of them twice this size. Such spheres had the advantage of lightness though often were frail in structure and liable to lose their perfect sphericity. [Illustration: Fig. 140. Terrestrial Globe Gores by Johannes Oterschaden, ca. 1675.] In the matter of special ornamentation or decoration, to be observed in globe mountings, individual taste was given unlimited freedom to express itself, and in certain instances it will have been noted that these mountings were exceedingly elaborate. Primarily we may say that globes were constructed for the useful purpose of promoting geographical and astronomical studies, generally recording the latest and best geographical or astronomical information and in form superior to that which could be set down on the plane map, but they also had a place of importance, secondary we may call it, on account of their decorative value. They came to be considered almost essential as adornments for the libraries of princes, of prosperous patricians, and of plodding students, and their mountings were often especially fashioned for the places they were to occupy. They seemed to lend an air of scholarly respectability; to suggest that their possessors wished to pay, certainly a modicum of homage to the sciences which globes were calculated to promote.