Terrestrial and Celestial Globes Volume Ii Part 15

Chapter XIV

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 Schoner, 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.

[Ill.u.s.tration: Fig. 133. Astrolabe.]

The princ.i.p.al 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 bra.s.s. 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 pa.s.sing 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]

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 bra.s.s, 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 b.a.l.l.s, 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 bra.s.s 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 b.a.l.l.s 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 Nurnberg an inst.i.tute 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. Bra.s.s, 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 ma.n.u.script 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 ma.n.u.script 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 pa.s.sed, and the engraved map found increasing favor, practically all globe b.a.l.l.s, 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-mache.

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 Germa.n.u.s 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 lat.i.tude and longitude vary in length, particularly those of longitude as one pa.s.ses 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 Waldseemuller 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 pa.s.sed other globe gore maps made their appearance, such as those undoubtedly the work of Schoner or of the Schonerian 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.

[Ill.u.s.tration: Fig. 134. Globe Gores of Henricus Glarea.n.u.s, 1527.]

The artist Albrect Durer (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 ill.u.s.trate 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 ill.u.s.tration, 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." Durer 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 resume 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 Durer had published his observations on this subject Henricus Loriti Glarea.n.u.s (1488-1551) issued a small treatise on geography,[196] devoting his Chapter XIX bearing t.i.tle '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 circ.u.mference of the globe they were intended to cover; the longer diameter of each gore representing the semicirc.u.mference 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 Glarea.n.u.s 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 pa.s.sed, 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.

Durer had proposed the employment of sixteen segments, Waldseemuller, Schoner, Boulengier, and Glarea.n.u.s had thought twelve a more suitable number. As the years pa.s.sed we find a preference manifesting itself now for twelve, now for sixteen, now for eighteen, twenty-four, or thirty-six with a more common preference for the smaller number. The several biangles for the maps alluded to above were fashioned to extend from pole to pole in what we may call the equatorial system; Mercator, as has been noted, introduced the novel idea of truncating his gores twenty degrees from each pole, preparing as a covering for the remaining polar s.p.a.ce a circular disc, having the required diameter of forty degrees.[198] This plan he proposed for the practical reason that a paper covering for a sphere so constructed could be applied with greater ease and with greater accuracy than one consisting of complete biangular figures, remembering the tendency of the paper to expand and the difficulty in avoiding folds.

As there was much inclination among map makers to experiment in the matter of map projection so there was an inclination to experiment, as the years pa.s.sed, in the matter of design for the globe gores. In the so-called Da Vinci gores we find them drawn in two groups of four each (Fig. 135), and instead of the globe biangle we have the globe equilateral triangle. Their application to a spherical surface could only have been made with difficulty, if at all; indeed we cannot be certain that in so outlining a map of the world the draughtsman's intention was to use it in globe construction. The plan seems never to have been followed by any of the other map makers, or by any globe maker. We find an interesting early instance in which the gore map construction was clearly employed merely as a method for plane map making, a method having certain very commendable features (Fig. 136).

The author of this map is unknown.

[Ill.u.s.tration: Fig. 135. Gore Map of Leonardo da Vinci, ca. 1515.]

[Ill.u.s.tration: Fig. 136. Anonymous Globe Gores in Plane Map Construction, ca. 1550.]

In referring to unusual forms in gore construction attention may again be called to the map of Alonso de Santa Cruz and to that of Antonius Floria.n.u.s, in which maps the plan was hemispherical,[199] the central point in the construction of each hemisphere, a northern and a southern, being the pole, the circ.u.mference of the circle in which the thirty-six gores were drawn, representing the equator. But again we do not know that such a gore map was ever employed in globe construction though the method, it seems, would lend itself to that end.

It can be readily understood that numerous modifications in the matter of globe-gore construction and their application to the surface of the sphere, more or less detailed in character, were introduced as the years pa.s.sed, but the modifications were by no means at all times in the line of improvement.[200] The technical skill of the present day does not surpa.s.s that which one occasionally finds exhibited in the work of some three hundred years ago.

In the matter of geographical record terrestrial globe maps stand with the plane maps of the same period. While they are by no means as numerous as the plane maps, there attaches to them an importance no less historically significant. Not infrequently they give us records not to be found elsewhere. In their general features, differences can hardly be said to exist between plane maps and globe maps. In the matter of adornment there is similarity; each following the practice of the time when constructed. As pictures and legends hold a place of prominence, particularly on mediaeval maps,[201] so even to the close of the period we have had under consideration, that is, the end of the eighteenth century, these adornments have place on globe maps, sometimes few, sometimes many, the same, if in picture, exhibiting the inhabitants of land and sea, if merely a legend, giving information of geographical importance on the terrestrial globe and of astronomical importance on the celestial, these legends being often placed in an artistic cartouch.

To the printed or engraved globe map, color was generally added by hand with an effect often very artistic, in contrast with which the modern machine methods of color printing are deplorably crude.

On most terrestrial globe maps meridian circles are represented at intervals of ten, twenty, or thirty degrees, the prime meridian on which the degrees of lat.i.tude are marked being usually made very conspicuous, and to the close of the period under consideration usually made to pa.s.s through the Cape Verde Islands or the Canaries, a point always to be carefully noted in attempting to get a reading for the longitude of any particular place. Parallels are usually drawn at intervals similar to those of meridians, the equator on which the degrees of longitude are marked, the tropics, and the polar circles being always conspicuous. The ecliptic or zodiac is usually indicated encircling the globe from the solst.i.tial point on the tropics, intersecting the equator at the two opposite equinoctial points, through which as through the solst.i.tial points the colures are made to pa.s.s.

Hues states that "Those lines which a ship, following the direction of the Magnetic Needle, describeth on the surface of the Sea, Petrus Nonius calleth in the Latin Rumbos, borrowing the appellation of his Countrymen the Portugals; which word, since it is now generally received by learned writers to express them by, we also will use the same," that is, rhumbs or rhumb-lines.

[Ill.u.s.tration: Fig. 137. Portrait of Johann Hevelius (Hevel).]

These were represented on the globe, first by Mercator, by greater or lesser circles or "winding lines," and were intended to be of aid to seamen in navigating from port to port across the great oceans. In their representation on the globe map cognizance was taken of the fact that all meridians of all places pa.s.s through both poles, crossing the equator therefore at right angles and all other circles parallel to it, and that if the navigator's course is in any other direction than toward one of the poles he is continually changing his horizon and his meridian. The rhumbs as drawn were made to cut all meridians of all places at equal angles and to respect the same quarters of the world, that is, direction, whatever the horizon. Rhumbs can represent great circles only when they coincide with the equator or with any meridian.[202]

In the matter of draughting, printing, and mounting celestial globe gore maps the method employed may in general be said to be identical with that followed in terrestrial globe construction. It should, however, be noted that in pasting the gores on the surface of the sphere they were often so applied as to have their points or angles meet at the pole of the ecliptic, in what may be called the ecliptic system, instead of applying them to meet at the poles of the equator, the globe itself being generally so mounted as to revolve in the equatorial system, its poles of revolution being attached to the meridian circle.[203]

The figures of the several constellations were usually drawn with care, occasionally with high artistic taste, as those drawn by Hevelius (Fig.

137) and copied by Gerhard and Leonhard Valk for their celestial globes (Fig. 138). The several stars represented on the map, the majority of them being either lettered or named, were usually from the first to the sixth magnitude, each represented in its proportional size, while an explanatory table for the several magnitudes was usually given on some one of the gores. The stars and the figures of the several constellations, let it be noted, were not made to appear on the surface of the sphere, with rare exceptions, in their relative location as they appear to the observer who beholds them from his position on the surface of the earth, but are reversed. To the astronomer the earth is but a point in s.p.a.ce, to the layman, so far as mere appearance is concerned, it is the center about which the starry heavens appear to revolve. With the pole (north for us in the northern hemisphere) as the center of the dial face the stars appear to move in a direction the reverse of that in which the hands of a clock are made to move. The astronomer, that is, the celestial globe maker, thinks of himself as placed beyond the vaulted heavens in which the stars appear to be located, and as looking down upon this vaulted dome as on the surface of his celestial globe. An ill.u.s.tration may here well serve us. As one observes serves Ursa Major on any starry night, which constellation we commonly call the Great Dipper, the bowl of the dipper, which is located in the body and flank of the bear, leads in its apparent motion around the pole star, being followed by the handle of the dipper or the tail of the bear (Fig. 139).

On the surface of the celestial sphere, however, the position of bowl and handle was usually reversed, the constellation appearing as it would to the beholder who finds himself beyond the stars. Naturally the planets could not be represented on the surface of a solid celestial sphere; only in the armillary sphere or the orrery could they find place. In these instruments we generally find them represented, each with its circle or orbit properly given, and relatively properly placed.

[Ill.u.s.tration: Fig. 138. Constellation Ursa Major.]

In the geographical records as they appear on the several terrestrial globe maps, it is to be admitted that the authors, with rare exceptions, undertook to set down what they thought to be fact, shall we say the real tangible geographical fact or facts. The maker of the star map, on the contrary, clearly gave his imagination play, not in his attempt to mark in the proper location the several stars as they came to be known and catalogued, but in the draughting of the figures of the several constellations. The imaginative figures of the ancients, of Eudoxus, of Aratus, of Ptolemy and others survived throughout the period we have had under consideration, and to the forty-eight constellations of Ptolemy others from time to time were added until more than one hundred have been named and figured. In general the several constellations, as the various astronomers and makers of star maps have conceived them, may be said to be identical, while some of the names which have been proposed have been accepted but for a time only and then rejected. Some of the groups to which names have been given have later been divided, thus giving rise to a new group name and to the draughting of an appropriate figure for this new group.[204]

Attention has been called to certain suggested changes in the names of constellations as given by the ancients, as for example those suggested by the Venerable Bede, by Johannes Bayer, by Julius Schiller proposing that biblical or Christian names should be subst.i.tuted for pagan names, and for these changes there was of course suggested an appropriate change in the figures for the several constellations. The proposal of Erhard Weigel has likewise been noted urging a subst.i.tution of the several coats of arms or heraldic devices of the European dynasties for the figures which had been so long and so generally accepted. There seems scarcely to be the need of stating that the names and figures of the ancients remain.[205]

A comparison of the work of the several artists who have set their hand to the draughting of figures for the numerous constellations is not without interest. Attention may here be directed in pa.s.sing to the decidedly oriental cast of these figures as they appear on Arabic globes.[206]

It is to be regretted that in the present very practical or scientific day the star map, wanting the figures of the constellations or giving them in but the faintest outline, has come to supplant the artistic and not unscientific creations of earlier years.

The earliest references we have to globes, that is, to solid b.a.l.l.s or spheres, make mention of their mountings, that is, to their encasing circles and their bases. The simplest mounting consisted of but a meridian and a horizon circle with probably a simple supporting base.

The earliest spheres were doubtless made to revolve just as the globes of today, around their polar axes which turn within sockets firmly attached to the meridian circle. This meridian circle of bra.s.s or wood was usually graduated from one to ninety degrees, that is, from the equator to the poles, and being adjustable relative to the horizon circle, a globe could be set with a polar elevation for any desired lat.i.tude. Those who have had occasion to refer to the construction and the uses of the globe more or less in detail, make mention of what they call its threefold position. In the first of these positions either pole may be at the vertical point, the equator and the horizon being parallel or coinciding. This they termed a parallel sphere. In the second position the equator and the horizon circle are set at right angles.

This they called a right sphere. In the third position, which was called an oblique sphere, the pole could be set at any elevation from zero to ninety degrees, counting from the horizon circle. In ill.u.s.tration of this third position it may be said that for the lat.i.tude of New York City, the north pole of the globe should be elevated 40 degrees 48 minutes above this circle.

More conspicuous by reason of its width and importance in the mounting of the globe than the meridian is the horizon circle. It is through notches in this circle at the north and south points that the meridian circle pa.s.ses, the notches also serving as gauges to keep the meridian from inclining more to the one side of the horizon circle than to the other. On the upper surface of this circle there were usually represented several concentric circles, the same being either engraved thereon, if it were of metal, and printed or pasted thereon if of wood, just as the globe map proper which covered the surface of the sphere.

The number of concentric circles, and the information carried in each, varied, nor was the order of the circles invariably the same. Those globes giving fullest information exhibit ten or more of these circles.

That one which was innermost and next to the body of the globe was divided into twelve parts, each part carrying the name of one of the signs of the zodiac with its character, and each divided into thirty equal parts or degrees, these being numbered by tens, as 0, 10, 20, 30.

Next to the circle of signs, always remembering that the order might vary, was that containing the calendar including the names of the months, as January, February, March, etc., the days of the week being either distinguished by numbers or names. The old calendar was likewise usually given and so represented as to show the beginning of each month ten days earlier than in the new calendar. Here also were given the names of the church festival days. In the next circle were the names of the winds or directions, and first the Greek, Latin or Italian names of the eight, twelve or sixteen winds, as Greco, Libeccio, Ponente, Maestro, and next the names or initials of the thirty-two compa.s.s directions, the same generally in English or Dutch abbreviations. It may further be noted that a compa.s.s was often fixed in the horizon circle's upper face.

[Ill.u.s.tration: Fig. 138. Constellation of Orion by Hevelius.]