Terrestrial and Celestial Globes Volume 2 / Their History and Construction Including a Consideration of their Value as Aids in the Study of Geography and Astronomy

by Edward Luther Stevenson

The Technic of Globe Construction—Materials and Methods

General problems to be met.—Development from the simple armilla to the complex sphere.—The references of Ptolemy, Leontius Mechanicus, Alfonso.—Behaim’s leadership in practical globe making.—Materials employed.—Experiments in map projection.—The beginning and rapid development of globe-gore construction.—Various examples of early gore maps.—Equatorial polar and ecliptic polar mountings.—Special features of celestial globe maps.—Globe mountings.—Varying sizes of globes.—The uses of globes.—Moon globes and planetariums.

IN this concluding chapter it is not proposed to consider in detail the technical features of globe construction, as these features have presented themselves in the long period which has been under review; the rather to give, somewhat in the nature of a summary, a general word as to the development of the simple armilla of the ancients, “in continued succession, receiving ripeness and perfection” in such celestial spheres as were those of Mohammed ben Helal, of Tycho, of Hondius, or of Blaeu; into the terrestrial spheres of Schöner, of Mercator, of Greuter, or of Coronelli.

We have seen that during these years there were problems mechanical, mathematical, and artistic continually arising, in the solution of which talent of a high order was often exhibited; problems having to do with the kind of material to be employed, with the shaping and the graduation of the rings or circles, with the construction of the supporting bases which entered into the completed product, with the engraving of the map on the surface of the metal sphere, or with the designing and the engraving of the plates for the printing of the map to be used in covering the prepared ball, and the fitting of the same to its curved surface.

The principal astronomical instrument employed by such ancient astronomers as Eudoxus, Timocharis, and Hipparchus appears to have been at first but a single metal ring, perhaps of brass. At any rate their instruments must have been exceedingly simple, perhaps the simplest form of the astrolabe (Fig. [133]), yet they sufficed as aids in the solution of such astronomical problems as suggested themselves in that early day. The addition of a second ring to the simple instrument gave further aid to the observer in his efforts to determine the declination and the right ascension of any of the heavenly bodies. These rings came to be considered, the first as a celestial meridian circle, the second as a celestial horizon circle, and in the passing years others were added to represent the ecliptic, the colures, the tropics, the polar circles, and the orbits of the several planets, until we have the fully developed armillary sphere of a Vopel or a Santucci.[181]

Fig. 133. Astrolabe.

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.