Relative to globes proper in antiquity, it will have been noted that in general there is an element of uncertainty as to their exact character, which speaks out in the numerous allusions to them. None has survived to our day save the Atlante Farnese. This globe of marble is not so mounted as to permit its revolution, resting as it does upon the shoulders of the mythical Atlas, yet in its representation of the figures of the several constellations, then recognized by astronomers, it differs practically but little from the celestial globes, that is, solid spheres, constructed a millennium and a half later.[182] We cannot, however, draw the conclusion from this one example that such globes were generally looked upon as practical instruments for use in astronomical studies, yet there clearly were those who did so regard them. Doubtless the globe or globes to which Ptolemy alludes were intended to be of practical value. He tells us they should be constructed of brass, and as before noted, he describes the use and the construction of such instruments. Like the maps he probably made, though none survives, it is not difficult, from his description, to reconstruct them. Such celestial globes as Ptolemy may have prepared were doubtless adjustable, but were not made to revolve by mechanical device such as we frequently meet with in globes of the seventeenth and the eighteenth centuries, nor were they like the mechanical contrivance of Archimedes, clearly intended to represent the movements of the celestial bodies, and perhaps their movements relative to the earth. No description of Archimedes’ mechanism survives by means of which it could now be reproduced with anything like a satisfactory degree of certainty. The allusions of Leontius Mechanicus, referred to in Chapter III, read like a globe maker’s instructions of the eighteenth century. He knew his Ptolemy whom he followed in the main, but he wrote as one who clearly did not sense the approaching decline of interest in the physical sciences. And what can be said of the methods and the materials for globe making during the period of the so-called middle ages? The survivals, and these are only of the later years of the period, are of Arabic origin, which, without exception, appear to have been intended primarily for use in astronomical studies. They are either armillary spheres, or metal balls, on the surface of which are the engraved representations of the starry heavens, with the figures of the several constellations. Without a known exception these are of small size, and if furnished at all with mounting, only that of a simple character. There is reason for thinking that such astronomical instruments were made in great numbers, and that they were to be found in practically all Arabic observatories.[183]