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]
The interesting allusions in King Alfonso’s ‘Libros del Saber de Astronomia,’ from which citations may be found in our Chapter IV, give us information concerning both methods and materials which might be employed in globe construction in his day. It is not there stated that the author had information concerning the actual use of the more than twenty named materials which might be chosen for their manufacture. He does, however, lead us to infer that there may have been experiments by his contemporaries in which trial was made of the fitness of the several materials named, his conclusion being that wood or brass was the most suitable.
It has previously been noted that globes appear to have been made now and then for use in the monastic schools, but we find no detailed description of their special character. Here and there, it is true, may be found reference to the adjustability of their parts, and to their rings which made them serviceable for furthering astronomical studies. The inference is fair that the globes of these Christian schools were armillary spheres, and were not solid or hollow balls on the surface of which the starry firmament or the earth had been depicted.
Behaim’s globe of the year 1492 seems to represent a radical departure in globe construction. His idea appears to have been novel. He employed a mould in the making of his globe ball, and over the surface of this completed ball pasted irregular strips of parchment which furnished a suitable ground for the draughting of the map with its geographical outlines and its artistic adornments in color. Behaim’s globe mounting was of the simplest character, consisting of a metal meridian circle within which the sphere could be revolved, a horizon circle of like material, the whole resting upon a tripod base. Although effort was made to establish in Nürnberg an institute wherein globe making might be taught especially, the plan seems not to have carried, and such as were later produced in this city were merely the output of the mathematical instrument maker’s shop or of the geographical establishments.
Throughout all the early years of the modern period, metal globes continued to find favor, to the making of which skilled workmen in the thriving industrial centers of Southern Germany, Southeastern France, Northern Switzerland, and Northern Italy set themselves. Brass, copper, silver, and gold were employed very frequently in their construction, the last-named metals being used in the making of globes primarily for ornamental purposes.[184] Globes with manuscript maps, as before noted, seemed to find especial favor in Italy, in the making of which much artistic skill was displayed. The spheres for such globes were usually of wood either solid or hollow, of well-fashioned strips of wood, canvas covered, the whole carefully glued and braced that the spherical shape might not be affected with time. In the preparation of the sphere to receive the manuscript map, workmen proceeded much as did Behaim, pasting over its surface irregular strips of parchment or paper, adding occasionally a groundwork of paint suitable for taking the sketch of the draughtsman. As the years passed, and the engraved map found increasing favor, practically all globe balls, with exceptions as noted above, were made either of plaster shot through and through with a binding material, usually of fiber, and fashioned over a mould, or of a preparation of papier-mâché.
The increasing interest in globes and globe making manifesting itself in the early years of the sixteenth century led to the devising of methods for their more rapid construction. If the opening years of the sixteenth century witnessed a rapid expansion of geographical knowledge, none the less did they witness an improvement in the making of maps wherein this expanding knowledge could fittingly be recorded. It is interesting to note how rapidly change was made from one method of map draughting to another in the search for a projection which might prove itself to be altogether suitable. As a result of this striving we have for example the projection of Donnus Nicolas Germanus employed in his maps of the geographer Ptolemy, and often referred to as the Donis projection.[185] Then we find the stereographic meridional[186] and the stereographic polar,[187] the cordiform single and double[188] which seem to have been a development from the orthographic projection well represented in the map of Johannes Stabius (Fig. [45]) who appears to have been the first to give the method prominence. In addition to the projections mentioned there were many modifications, to suit the notions of the draughtsmen, which were employed in the early sixteenth century.[189] With the fuller realization of the fact that the earth is a sphere, the desire accurately to represent in the maps its spherical surface continued to seek for expression, an expression that would do least violence to the fact that the degrees of latitude and longitude vary in length, particularly those of longitude as one passes from the equator toward the poles or from the poles toward the equator. If the earth is a sphere then why could a map so draughted as truly to represent the surface of a sphere not be counted the most acceptable? This must have been the argument of those who especially applied themselves to the designing of maps suitable for a spherical surface, that is, for application to a globe ball.
Who first conceived the idea of fashioning globe gore maps we do not know. Fiorini cites evidence[190] that Francesco Rosselli (1445-1510), a printer of large and small maps in Florence, included in his productions gore maps to be used in globe construction, and this probably before the year 1507, but none of his work of this character has come down to us. The so-called Waldseemüller gores are the oldest known, of which but one copy is extant.[191] By some they are thought to have been constructed for his globe to which he refers in his ‘Cosmographiae Introductio,’ but they are unsigned and undated. They are somewhat crude and much manipulation would be required to fit them to the surface of a sphere. Before the first quarter of the sixteenth century had passed other globe gore maps made their appearance, such as those undoubtedly the work of Schöner or of the Schönerian school, or such as the gores of Boulengier[192] exquisitely engraved and printed, though so far as we know never used in covering the surface of a sphere.
The artist Albrect Dürer (1471-1528), as we are informed, was one of the earliest to set himself to the solution of the problem having to do with the development of a spherical surface into a flat surface, yet he never seems to have thought an exact mathematical solution possible. It was a problem, he realized, in which there could be but an approximate solution. In trying to illustrate what he thought to be the nearest approach to the same he found himself led to the idea of the globe gore.[193] Of his illustration, he said, “Die sphera oder ein Kugel wenn man sie durch jr mittag linien zerschneydet, und in Planum legt, so gewinnt sie ein Gestalt eines Kam, wie ich das hie hat auffgerissen.” “Should one divide the sphere or ball on the line of the equator and lay this out as a plane, one has the figure of a comb, as is here shown.” Dürer worked out a simple rule for the construction of the globe biangles,[194] which rule served measurably well for the purpose intended. While it would not be inappropriate to give here a résumé of his formula, as well as the formulae of others who set themselves to a like task, we should in so doing be carried into a field rather more technical than seems fitting for our purpose.[195]
Two years after Dürer had published his observations on this subject Henricus Loriti Glareanus (1488-1551) issued a small treatise on geography,[196] devoting his Chapter XIX bearing title ‘De inducendo papyro in globo’ to globe-gore construction. He proposed the employment of twelve gores or biangles (Fig. [134]) so arranged for printing that the shorter diameter of each should represent 30 degrees of longitude, the sum therefore representing 360 degrees or the equatorial circumference of the globe they were intended to cover; the longer diameter of each gore representing the semicircumference of the globe and extending from pole to pole, that is, a meridian. We do not know that his formula for gore construction was closely followed by any globe maker of the period, nor does Glareanus himself appear to have attempted a practical application of his method, at least we have no evidence that he ever actually attempted to construct a globe. He, however, had made an important contribution toward the solution of the problem of how best to multiply these instruments which were increasingly recognized as of great value in geographical and astronomical studies. The general method of gore map making rapidly found favor despite such practical difficulties, for example, as arose from the peculiarity inseparable from the quality inherent in any and all paper, that is, its irregular expansion when moistened. This difficulty the globe makers, of course, were continually seeking to overcome or reduce to a minimum, as the years passed, through a careful selection of paper to be used, through a more skilful manipulation of the paper made moist by the application of the paste or glue employed in attaching the map to the surface of the sphere,[197] and through a more careful working out of the mathematical problem having to do with the proper proportions of each of the gores.