Russel Wallace : Alfred Russell Wallace (sic)
It is proposed that the globe shall always be kept up to the latest knowledge of the day, by adding fresh details from the results of new explorations in every part of the world; so that, by means of photography, maps of any country or district could be formed on any scale desired; and for a small fee the globe might be available to all map-makers for that purpose. Such maps would be more accurate than those drawn by any method of projection, while the facility of their construction would render them very cheap, and would thus be a great boon to the public, especially whenever attention was directed to any particular area.
M. Reclus states the scientific and educational value of such a globe as due to the following considerations--(1) its accuracy of proportion in every part, as compared with all our usual maps, especially such as represent continents or other large areas; (2) the unity of presentation of all countries, by which the erroneous ideas arising from the better known countries being always given on the largest scale will be avoided; and (3), that the true proportions of all the elevations of the surface will be made visible, and thus many erroneous ideas as to the origin, nature, and general features of mountain ranges, of valleys, and of plateaux will be corrected. He has fixed upon the scale of one hundred thousandth for several reasons. In the first place, it gives the maximum size of a globe that, in the present state of engineering science, can probably be constructed, or that would be in any case advisable; secondly, it is the scale of a considerable number of important maps in various parts of the world; and, thirdly, it is the smallest that would allow of very moderate elevations being modelled on a true scale. He considers that even Montmartre at Paris and Primrose Hill at London would be distinctly visible upon it under a proper oblique illumination.
When, however, we consider the size of such a globe, nearly four hundred and twenty feet in diameter, it is evident that both the difficulties and the cost of its construction will be very great; and both are rendered still greater by the particular design adopted by M. Reclus--a design which, in the opinion of the present writer, is by no means the best calculated to secure the various objects aimed at. I will therefore first briefly describe the exact proposals of M. Reclus as set forth in his interesting and suggestive pamphlet, and will then describe the alternative method, which seems to me to be at once [[p. 732]] simpler, less costly, and more likely to be both popular and instructive.
The essential features of the proposed globe are said to be as follows. Nothing about it must destroy or even diminish its general effect. It must not therefore rest upon the level ground, but must be supported on some kind of pedestal; and it must be so situated as to be seen from a considerable distance in every direction without any intervening obstruction by houses, trees, &c. But, in our northern climate, the effects of frost and snow, sun and wind, dust and smoke, rain and hail, would soon destroy any such delicate work as the modelling and tinting of the globe; it is therefore necessary to protect it with an outer covering, which will also be globular, its smooth outer surface being boldly and permanently coloured to represent all the great geographical features of the earth, so as to form an effective picture at a considerable distance. In order to allow room for the various stairs and platforms which will be required in order to provide for access to every part of the surface of the interior globe, and to afford the means of obtaining a view of a considerable extent of it, there is to be a space of about fifty feet between it and its covering, so that the latter must have an inside diameter of about five hundred and twenty feet. It is also to be raised about sixty feet above the ground, so that the total altitude of the structure will be not far short of six hundred feet.
M. Reclus adds to his general description a statement furnished by a competent engineer giving a general estimate for the erection of the globe, with some further constructive details, which are, briefly, as follows: Both the globe and the envelope are to be built up of iron meridians connected by spiral bands, leaving apertures nowhere more than two metres wide. The envelope is to be covered with thick plates of glass, and either painted outside on a slightly roughened surface, or inside with the surface remaining polished, either of which methods are stated to have certain advantages with corresponding disadvantages. The envelope being exposed to storms and offering such an enormous surface to the wind would not be safe on a single pedestal. It is therefore proposed to have four supports placed about 140 feet apart, and built of masonry to the required height of 60 feet. The globe itself is to have a surface of plaster, on which all the details are to be modelled and tinted, the oceans alone being covered with thin glass. In order to provide access to every part of the surface of the globe it is proposed to construct in the space between the globe and its covering, but much nearer to the former, a broad platform, ascending spirally from the South to the North Pole in twenty-four spires, with a maximum rise of one in twenty. The balustrade on the inner side of this ascending platform is to be one metre (3 feet 3 inches) from the surface of the globe, and the total length of the walk [[p. 733]] along it will be about five miles. But as the successive turns of this spiral pathway would be about 20 feet above each other, the greater part of the globe's surface would be at too great a distance, and would be seen too obliquely, to permit of the details being well seen. It is therefore proposed that the globe should rotate on its polar axis, by which means every part of the surface would be accessible, by choosing the proper point on the platform and waiting till the rotation brought the place in question opposite the observer. But as such an enormous mass could only be rotated very slowly, and even more slowly brought to rest, this process would evidently involve much delay and considerable cost. Again, as the facility of producing accurate maps by photography is one of the most important uses which the globe would serve, it is clear that the spiral platform, with its balustrade and supporting columns, would interfere with the view of any considerable portion of the surface. To obviate this difficulty it is stated that arrangements will be made by which every portion of the spiral platform may be easily raised up or displaced, so as to leave a considerable portion of the globe's surface open to view without any intervening obstruction. In order that this removal of a portion of the roadway may not shut off access to all parts of the globe above the opening, eight separate staircases are to be provided by means of which the ascent from the bottom to the top of the globe may be made.
This account of the great earth-model proposed by M. Reclus clearly indicates the difficulties and complexities in the way of its realisation. We are required to erect, not one globe, but two, the outer one, to serve mainly as a cover for the real globe, being very much larger, and therefore much more costly, than the globe itself. Then we have the eight staircases of twenty-four flights each, and the five or six miles of spiral platform, wide enough to allow of a pathway next the surface of the globe and a double line of road outside for the passage of some form of auto-motor carriages. Then, again, the greater part of this huge spiral platform is to be in movable sections, which can be either swung aside or lifted up in order to allow of an uninterrupted view of any desired portion of the globe's surface. But even this will not suffice to get an adequate view of the globe in all its parts, and this enormous mass is to be rendered capable of rotating on a vertical axis. It is suggested that this rotation shall be continuous in the space of a sidereal day, and it is thought that it will be so slow as not to interfere with any photographic operations that may be desired.
But a little consideration will show us that, even with all these complex constructions and movements, and supposing that they all work with complete success, the main purposes and uses of the globe, as laid down by M. Reclus himself, would be very imperfectly attained. [[p. 734]] His first point is that such a globe would correct erroneous ideas as to the comparative size and shape of different regions due to the use of Mercator's or other forms of projection. But in the globe as proposed no comparison of different countries, unless very near together, would be possible; and even if considerable portions of the platform could be removed, and the observer could be placed near the outer covering, at a distance of, say, 40 feet from the globe, only a comparatively small area could be seen or photographed in its accurate proportions. If we take a circle of 40 feet diameter as our field of view it is evident that all the marginal portion would be seen very obliquely (at an angle of 30 from the perpendicular if the surface were flat, but at a somewhat greater angle owing to the curvature of the surface), and would also be on a smaller scale owing to their greater distance from the instrument, so that the central portions only would be seen in their true proportionate size and shape. For ordinary views this would not much matter, but when we have to produce maps from a globe which is estimated to cost somewhere about a million sterling, and one of whose chief uses is to facilitate the production of such maps, a high degree of accuracy is of the first importance. In order to attain even a fair amount of accuracy comparable with that of a map on any good projection, we should probably have to limit the area to a diameter of about 10 feet, equal to about 190 or 200 miles, so that even such very limited areas as Scotland or Ireland would be beyond the limits of any high degree of accuracy. Larger areas, such as the British Isles, France, or Germany, would be quite beyond the reach of any accurate reduction by means of photography. As affording exceptional facilities for accurate map-making the globe would be of very limited service.
The second advantage to be derived from the proposed globe is stated to be the correction of erroneous ideas as to the comparative sizes of various countries and islands, owing to the fact of their representation in atlases on very different scales, while each country gives its own territories the greatest prominence. But a large part of this advantage would be lost owing to the fact that distant countries could never be seen together. That Texas is much larger than France would not be impressed upon the spectator when, after losing sight of the one country several hours might pass before he came in sight of the other, while even the various States of Europe, such as Great Britain and Italy, or Portugal and Turkey, would never be in view at the same time. For this special purpose, therefore, the globe would not be so instructive as the large wall maps of continents at present used in every schoolroom.
The third advantage, that the globe would admit of the varied contours of the surface being shown in their true proportions, does undoubtedly exist, and is very important; but even as regards this [[p. 735]] feature, its instructiveness would be very largely diminished by the impossibility of seeing the contours of any considerable area in its entirety, or of comparing the various mountain ranges with each other, or even the different parts of the same mountain range. It may be doubted whether the relief-maps now made do not give as useful information as would be derived from a globe of which only so limited a portion could be seen at one view.
It thus appears that the gigantic earth-model proposed by M. Reclus would very imperfectly fulfil the purposes for which he advocates its construction. But this defect is not at all inherent in a globe of the dimensions he proposes, but only in the particular form of it which he appears to consider to be alone worthy of consideration. I believe that such a globe can be made which shall comply with the essential conditions he has laid down, which shall be in the highest degree scientific and educational, which shall be a far more attractive exhibition than one upon his plan, and which could be constructed for about one-third the amount which his double globe would cost. It would only be necessary to erect one globe, the outer surface of which would present a general view of all the great geographical features of the earth, while on the inner surface would be formed that strictly accurate model which M. Reclus considers would justify the expense of such a great work, and which, as I shall presently show, would possess all those qualities which he postulates as essential, but which the globe described by him would certainly not possess.
I make no doubt that the eminent geographer would at once put his veto upon this proposal as being wholly unscientific, unnatural, and absurd. He would probably say that to represent a convex body by means of a concave surface is to turn the world upside-down, or rather outside-in, and is fundamentally erroneous; that it must lead to false ideas as to the real nature of the earth's surface, and that it cannot be truly educational or scientifically useful. But these objections, and any others of like nature, are, I venture to think, either unsound in themselves or are wholly beside the question at issue. M. Reclus has himself declared the objects of the gigantic earth-model and the educational and scientific uses it should fulfil. I take these exactly as he has stated them, and I maintain that if the plan proposed by me can be shown to fulfil all these requirements, then it can not be said to be less scientific, or less instructive, than one which can only fulfil them in a very inferior degree.
Before showing the overwhelming advantages of the concave over the convex globe for all important uses, I would call attention to two strictly illustrative facts. Celestial globes have been long in use, and I am not aware that it has ever been suggested that they are unscientific and deceptive, and they ought to be abolished. Positions seen on such a globe can be, and are, easily transferred to the [[p. 736]] apparently concave sky; while many problems relating to the motions the earth and the planets are clearly illustrated and explained by their use. A concave surface suspended from the ceiling of a school-room would, doubtless, show more accurately the position of the heavenly bodies, but would probably not be so generally useful as the unnatural convex globe.
The representation of the earth's surface on the inside of a sphere has been tried on a considerable scale by Wyld's globe in Leicester Square, and was found to be extremely interesting and instructive. Before seeing it I was prejudiced against it as being quite opposed to nature; but all my objections vanished when I entered the building and beheld the beautiful map-panorama from the central gallery. I visited it several times, and I never met with any one who was not delighted with it, or who did not find it most instructive in correcting the erroneous views produced by the usual maps and atlases. It remained for twelve years one of the most interesting exhibitions in London, when it was removed owing to the lease of the ground having expired. This globe was sixty feet in diameter, and it showed how grand would be the effect of one many times larger and admitting of greater detail, and of more striking effects by the view at different distances and under various kinds of illumination.
One other consideration may be adduced in this connection, which is, that even the outer surface of a huge globe has its own sources of error and misconception. It would perpetuate the idea of the North-pole being up and the South-pole down, of the surface of the earth being not only convex but sloping, while for the whole southern hemisphere we should have to look upwards to see the surface, which we could never do in reality unless we were far away from that surface. Again, we all know how the sea-horizon seen from an elevation appears not convex but concave. A convex globe, therefore, will not represent the earth as we see it, or as we can possibly see it; and to construct such a globe with all the details of its surface clearly manifest, while at the same time we see the convexity and have to look up to some parts of the surface and down upon others, really introduces fresh misconceptions while getting rid of old ones. We cannot reproduce in a model all the characteristics of the globe we live on, and must therefore be content with that mode of representation which will offer the greater number of advantages and be, on the whole, the most instructive and the most generally useful. This, I believe, is undoubtedly the hollow globe, in which, however, the outer surface would be utilised to give a general representation of the earth as proposed by M. Reclus, and which would no doubt be a very interesting and attractive object.
I will now proceed to show, in some detail, how the concave [[p. 737]] surface of a hollow globe is adapted to fulfil all the purposes and uses which M. Reclus desires.
We should, in the first place, be able to see the most distant regions in their true relative proportions with a facility of comparison unattainable in any other way. We could, for instance, take in at one glance Scandinavia and Britain, or Greenland and Florida, and by a mere turn of the head could compare any two areas in a whole hemisphere. Both the relative shape and the relative size of any two countries or islands could be readily and accurately compared, and no illusion as to the comparative magnitude of our own land would be possible. In the next place, the relief of the surface would be represented exactly as if the surface were convex, but facilities for bringing out all the details of the relief by suitable illumination would be immensely greater in the hollow globe. Instead of being obliged to have the source of illumination only fifty feet from the surface, it could be placed either at the pole or opposite the equator at a distance of two hundred or three hundred feet, and be easily changed so as to illuminate a particular region at any angle desired, and to render visible the gentlest undulations by their shadows. Of course, electric lighting would be employed, which by passing through slightly tinted media might be made to represent morning, noon, or evening illumination.
It is, however, when we come to the chief scientific and educational use of such a globe, the supply of maps of any portion of the earth on any scale, by means of photography, that the superiority of the concave model is so overwhelming as to render all theoretical objections to it entirely valueless. We have seen that on the convex surface of a globe such as M. Reclus has proposed, photographic reproductions of small portions only would be possible, while in areas of the size of any important European State, the errors due to the greater distance and the oblique view of the lateral portions would cause the maps thus produced to be of no scientific value. But, in the case of the concave inner surface of a sphere, the reverse is the case, the curvature itself being an essential condition of the very close accuracy of the photographic reproduction. A photograph taken from anywhere near the centre of the sphere would have every portion of the surface at right angles to the line of sight, and also at an equal distance from the camera. Hence there would be no distortion due to obliquity of the lateral portions, or errors of proportion owing to varying distances from the lens. We have, in fact, in a hollow sphere with the camera placed in the centre, the ideal conditions which alone render it possible to reproduce detailed maps on the surface of a sphere with accuracy of scale over the whole area. For producing maps of countries of considerable extent the camera would, therefore, be placed near the centre, but for maps of smaller areas on [[p. 738]] a larger scale, it might be brought much nearer without any perceptible error being introduced, while even at the smallest distances and the largest scale the distortion would always be less than if taken from a convex surface. It follows that only on a concave globular surface would it be worth the expense of modelling the earth in relief with the greatest attainable accuracy, and keeping it always abreast of the knowledge of the day, since only in this way could accurate photographic reproductions of any portions of it be readily obtained. For absolute accuracy of reduction the sensitive surface would have to be correspondingly concave, and this condition could probably be attained.
I will now point out how much more easily access can be provided to every part of the surface of a concave than to that of a convex globe. Of course, there must be a tower in the position of the polar axis. This would be as small in diameter as possible consistent with stability, and with affording space for a central lift; and it would be provided with a series of outside galleries supported on slender columns, at regular intervals, for affording views of the whole surface of the globe. This general inspection might be supplemented by binocular glasses with large fields of view and of varying powers, by means of which all the details of particular districts could be examined. For most visitors this would be sufficient; but access to the surface itself would be required, both for purposes of work upon it, for photographing limited areas at moderate distances, and for close study of details for special purposes. This might be provided without any permanent occupation of the space between the central tower and the modelled surface, in the following manner.
Outside the tower and close to it will be fixed, at equal distances apart, a series of three or four circular rails, on which will rest by means of suitable projections and rollers, two vertical steel cylinders, exactly opposite to each other and reaching to within about ten feet of the top and bottom of the globe, with suitable means of causing them slowly to revolve. Attached to these will be two light drawbridges, which can be raised or depressed at will, and also, when extended, will have a vertical sliding motion from the bottom to the top of the upright supports. The main body of this drawbridge would reach somewhat beyond the middle point from the tower to the globular surface, the remaining distance being spanned by a lighter extension sliding out from beneath the main bridge and supported by separate stays from the top of the tower. When not in use, the outer half would be drawn back and the whole construction raised up vertically against the tower. The two bridges being opposite each other, and always being extended together, would exert no lateral strain upon the tower.
By means of this arrangement, which when not in use would leave [[p. 739]] the whole surface of the globe open to view, access could be had to every square foot of the surface, whether for purposes of work upon it or for close examination of its details; and, in comparison with the elaborate and costly system of access to the outer surface of a globe of equal size, involving about five miles of spirally ascending platform and more than a mile of stairs, besides the rotation of the huge globe itself, is so simple that its cost would certainly not be one-twentieth part of the other system. At the same time, it would give access to any part of the surface far more rapidly, and even when in use would only obstruct the view of a very small fraction of the surface.
A few words may be added as to a mode of construction of the globe different from that suggested in the project of M. Reclus. It seems to me that simplicity and economy would be ensured by forming the globe of equal hexagonal cells of cast steel of such dimensions and form that when bolted together they would build up a perfect sphere of the size required. As the weight and strain upon the material would decrease from the bottom to the top, the thickness of the walls of the cells and of the requisite cross struts might diminish in due proportion while the outside dimensions of all the cells were exactly alike. At the equator, and perhaps at one or two points below it, the globe might be encircled by broad steel belts to resist any deformation from the weight above. A very important matter, not mentioned by M. Reclus, would be the maintenance of a nearly uniform temperature, so as to avoid injury to the modelling of the interior by expansion and contraction. This might be secured by enclosing the globe in a thick outer covering of silicate or asbestos packing, or other non-conducting material, over which might be formed a smooth surface of some suitable cement, on which the broad geographical features of the earth might be permanently delineated. With a sufficiency of hot-water pipes in and around the central tower, and efficient arrangements for ventilation, the whole structure might be kept at a nearly uniform temperature at all seasons.
It has now, I think, been shown that the only form of globe worth erecting on a large scale is one of which the inner surface is utilised for the detailed representation and accurate modelling of the geographical features of the earth's surface; but as to the dimensions of such a globe there is room for much difference of opinion. I am myself disposed to think that the scale of 1/100000, proposed by M. Reclus, is much too large, and that for every scientific and educational purpose, and even as a popular exhibition, half that scale would be ample. The representation of minute details of topography due to human agency, and therefore both liable to change and of no scientific importance--such as roads, paths, houses, and enclosures--would be out of place on such a globe, except that towns and villages and main lines of communication might be unobtrusively indicated. And for [[p. 740]] adequately exhibiting every important physiographical feature--the varied undulations of the surface in all their modifications of character, rivers and streams with their cascades and rapids, their gorges and alluvial plains, lakes and tarns, swamps and peat-bogs, woods, forests, and scattered woodlands, pastures, sand dunes and deserts, and every other feature which characterises the earth's surface, a scale of 1/200000th, or even one of 1/250000th, would be quite sufficient. And when we consider the difficulty and expense of constructing any such globe, and the certainty that the experience gained during the first attempt would lead to improved methods should a larger one be deemed advisable, there can, I think, be little doubt that the smaller scale here suggested should be adopted. This would give an internal diameter of 167 feet, and a scale of almost exactly a quarter of an inch to a mile, and would combine grandeur of general effect, scientific accuracy, and educational importance, with a comparative economy and facility of construction which would greatly tend to its realisation. It is with the hope of showing the importance and practicability of such a work that I have ventured to lay before the public this modification of the proposal of M. Reclus, to whom belongs the merit of the first suggestion and publication. Now that Great Wheels and Eiffel Towers are constructed, and are found to pay, it is to be hoped that a scheme like this, which in addition to possessing the attractions of novelty and grandeur, would be also a great educational instrument, may be thought worthy of the attention both of the scientific and the commercial world.