National Geographic Magazine/Volume 1/Number 3/Topographic Models

by Cosmos Mindeleff

TOPOGRAPHIC MODELS.

By Cosmos Mindeleff.

Of the many methods by which it has been sought to represent the relief of a country or district, only two have been at all widely used. These methods are, in the order of their development, by hachured and by contoured maps. Both have advantages and both have serious disadvantages. Without entering into the controversy that is even yet raging over the relative merits of the two systems, some slight notice of what each claims to accomplish is necessary.

The representation of relief by hachures is a graphic system, and in the best examples we have is an attempt to show, upon a plane surface, the actual appearance of a given area under given conditions of lighting,—as in the Dufour map of the Alps. Of course certain details that would really disappear if the assumed conditions were actual ones, must be shown upon the map,—so that it is, after all, but a conventional representation. The very best examples are, for this and other reasons, unsatisfactory, and far more so is this the case in the vastly larger class of medium grade and poor work.

The contour system represents relief by a series of lines, each of which is, at every point throughout its length, at a certain stated elevation above sea-level, or some other datum-plane; in other words, each contour line represents what would be the water's edge, if the sea were to rise to that elevation. It possesses the advantage of great clearness, but fails to a large degree in the representation of surface detail; moreover, one must have considerable knowledge of topography, in order to read the map correctly.^[1]

To those who must give first place to the quantity of relief rather than the quality, as, for example, the geologist or the engineer, a contoured map is now considered essential. On the other hand, where quality of relief is the prime consideration and the quantity a secondary one, as, for example, for the use of the army, a hachured map is considered the best. The method of hachures may be roughly characterized as a graphic system with a conventional element, and the contour method as a conventional system with a graphic element,—for if the contour interval is small enough a sort of shading is produced which helps considerably the idea of relief.

In addition to these two great systems, with which everyone is more or less familiar, there is another method of representing a country or district,—a method that succeeds where others fail, and which although by no means new, has not received the attention it deserves: this is the representation of a country by a model in relief. Certain striking advantages of models over maps of all kinds are, indeed, so apparent that one almost loses sight of such slight disadvantages as can, of course, be urged against them. In the graphic representation of the surface they are far superior to the hachured map, and they have the further advantage of expressing the relative relief, which the hachured map fails to do, except in a very general way. They have also the advantage of showing actual shadows, exactly as they would be seen in a bird's-eye view of the district, instead of more or less conventional ones, and are, consequently, more easily comprehended by the layman, without becoming any less valuable to the skilled topographer. In short, they combine all the graphic features of a hachured map with all the advantages of the best class of contoured maps, and in addition they show more of the surface detail, upon which so much of the character of the country depends and which is very inadequately expressed by hachures and almost completely ignored in a contoured map of large interval. The contours themselves can be made to appear upon the model very easily and without interfering with other features.

The uses of models are many and various. Within the past few years their usefulness has been much extended, and, now that they are becoming better known, will probably receive a still further extension. To the geologist they are often of great value in working out the structure of complicated districts, for the reason that so many important structural relations can be presented to the eye at a single glance. Similarly, for the graphic presentation of results there is no better method, as the topography, the surface geology, and any number of sections can be shown together and seen in their proper relationship. To the engineer an accurate model is often of the greatest assistance in working out his problems, and it is simply invaluable to explain the details of a plan to anyone who has little or no technical training; for, as has been stated, a model is easily comprehended by anyone, while more or less technical knowledge is required for the proper understanding of even the best maps.

I might go on cataloguing in detail the many uses to which models may be put, but shall now mention only one more—perhaps the most important of all—their use in the education of the young. No method has yet been devised that is capable of giving so clear and accurate a conception of the principles of physical geography as a series of well selected models; models have, indeed, already been used for this purpose, but unfortunately their great cost has prevented their general use in schools. Since, however, the study of geography has been placed upon a new basis and a new life has been infused into it, many men have given their attention to the subject of models, and have experimented with a view to cheapen the cost of reproduction, which has hitherto prevented their wide distribution; and probably this objection will soon be remedied. The ability to read a map correctly,—to obtain from a study of the map a clear conception of the country represented,—is more uncommon than is usually supposed. Some of the recent methods of teaching geography are intended to cultivate this very faculty, but it is doubtful whether there is any better method than that which consists in the study of a series of good models in conjunction with a series of maps, all on the same scale and of the same areas. The value of a series of good models in teaching geology is so apparent that it need only be mentioned. It is often, for reasons stated above, far more valuable even, than field instruction.

For the construction of a good relief map the first requisite is a good contoured map. To this should be added, when possible, a good hachured map, upon which the elevations of the principal points are stated,—if the interval in the contoured map is a large one,—and as much material in the way of photographs and sketches as it is possible to procure. The modeler should, moreover, have some personal acquaintance with the region to be represented, or, failing that, a general knowledge of topographic forms, and at least a clear conception of the general character of the country which he seeks to represent. This is very important, for it is here that many modelers fail: the mechanical portion of the work any ordinarily intelligent person can do. A model may be as accurate as the map from which it is made, every contour may be placed exactly where it belongs, and yet the resulting model may be,—indeed, often is—"flat," expressionless, and unsatisfactory. Every topographer in drawing his map is compelled to generalize more or less, and it is fortunate for the map if this be done in the field instead of in the draughtsman's office. But topographers differ among themselves: there may be, and often is, considerable difference in two maps of the same region made by different men; in other words, the "personal equation" is a larger element in a map than is usually supposed. This being the case, there is something more required in a modeler than the mere transferring of the matter in the map,—giving it three dimensions instead of two: he must supply through his special knowledge of the region (or, failing that through his general knowledge) certain characteristics that do not appear upon the map, and undo, so far as it is necessary, certain generalizations of the topographer and draughtsman. This artistic or technical skill required correctly to represent the individuality of a given district is especially important in the modeler; it is more important, perhaps, in small-scale maps of large districts than in large-scale maps of small ones,—for in the latter the generalizing process has not been carried so far, and the smaller interval of the contour lines preserves much of the detail.

The methods by which relief maps are made have always received more attention than would, at first sight, appear to be their proper proportion. It may be due, however, to the difficulty of applying any test to determine the accuracy of the finished model, and perhaps also to the general impression that any one can make a relief map,—and so he can, though of course there will be a wide difference in the value of the results. Some, indeed, have devoted their attention to methods exclusively, letting the result take care of itself,—and the models show it. There is no more reason why a modeler should tie himself down to one method of work, than that a water-colorist, or a chemist, or anyone engaged in technical work, should do so; though in some cases he might be required, as the chemist is, to show his methods as well as his results.

One of the earliest methods, with any pretension to what we may term mechanical control, is that described by the Messrs. Harden in a paper on "The construction of maps in relief," read before the American Institute of Mining Engineers in 1887. The method was published in 1838. Upon a contoured map as a basis cross-section lines are drawn at small and regular intervals, and, if the topography be intricate, corresponding lines at right angles. The sections thus secured are transferred to thin strips of some suitable material, such as cardboard or metal, and cut down to the surface line,—the strips themselves thus forming the cross-sections. These cross-sections are mounted upon a suitable base-board, and the cavities or boxes are then filled up with some easily carved material, such as plaster or wax. The top is then carved down to the form of the country or district,—the necessary guidance being obtained by the upper edges of the strips that form the cross-sections. It will be readily seen that this method is a very crude and laborious one. It necessitates in the first place a good contoured map upon which to draw the sections, but sacrifices much of the advantage thus gained because only a number of points on each contour line are used, instead of the entire line. It is no better, although actually more laborious, than the later method of driving contour pins (whose height above a base-board may be accurately measured,) along the contour lines, and then filling in. A slight modification of the latter method can be used to advantage when no contoured map is available, and when the points whose elevation is known are not numerous enough to permit the construction of one. In this case the only control that can be secured is by means of a number of pins driven into the base-board at those points whose elevation is known. The remainder of the map is then sketched in. This method is perhaps as satisfactory as any, when the material upon the map is scanty. Another method, however, growing out of the same scantiness of material, is in some cases to be preferred, especially for large models. The map is enlarged to the required size, and a tracing of it is mounted upon a frame. Another deep frame, just large enough to contain the mounted tracing, is made, and laid upon a suitable base-board upon which a copy of the map has been mounted. Upon this base-board the model is then commenced, in clay or wax. The low areas are modeled first,—horizontal control being obtained by pricking through the mounted tracing of the map with a needle point, and vertical control by measuring down from a straight edge sliding on the top of the deep frame. This system is rather crude, and only useful where the material upon the map is very scanty, but it gives excellent control.

A method used by Mr. F. H. King in the preparation of his large map of the United States is described by him in a letter to Messrs. Harden, and published by them in the place mentioned. A solid block of plaster is used,—the contoured map being transferred to it—and the plaster is carved down to produce a series of steps like those made by building up the contours. The shoulders are then carved down to produce a continuous surface. This method is one of the best of those that require carving instead of modeling.

Many other methods of producing relief maps might be mentioned, but, as most of them have been used only to make special models, they need not be described. The method that has been more used than any other still remains to be described. It is that which the writer has used almost exclusively, and consists in building up the model and modeling the detail, instead of carving it. It is a maxim of the modeler that the subject should be built up as far as possible, should be produced by adding bits of clay or wax, or other material, and not by carving away what is already on,—by addition and not by subtraction. This may be illustrated by a reference to the methods of the sculptor. The bust, or figure, or whatever the subject may be, is first modeled in clay or wax; from this model a plaster mould is made, and from this mould a plaster cast is taken. This cast is called the original, and the finished production, whether in marble, bronze, or any other hard substance, is simply a copy of this original. No one ever attempts to produce the finished bust or figure directly from the object itself. Even where the artist has for a guide a death mask, the procedure does not change. The bust is first made in clay, and this clay model, as a rule, contains all the detail which subsequently appears in the finished bust. It seems strange, therefore, that the relief map maker should use a method which the sculptor, with infinitely more skill and judgment, is afraid to use; and this on subjects that do not differ as much as might be imagined.

The contour interval to be used depends on the use to which the model is to be put. It is not always necessary to carry into the model all the contour lines upon the map: I may go further and say, that it is not always desirable to do so. The number to be used depends to some extent on the skill of the modeler. As already stated, the contours are only a means of control, and one modeler requires more than another. To build into a model every contour in a contoured map of ten foot interval is a very laborious proceeding, and not worth the time it takes, as in nine out of ten maps of such interval only the fifty-foot or the one hundred-foot curves are definitely fixed, the intermediate lines being merely filled in. This filling in can be done as well, or better, by the modeler.

The question as to the proper amount of exaggeration to be given the vertical scale, as compared with the horizontal, is the question about which has raged most of the controversy connected with relief map making. This controversy has been rather bitter; some of the opponents of vertical exaggeration going to the length of saying that no exaggeration is necessary, and that "he that will distort or exaggerate the scale of anything will lie." On the other hand the great majority of those who have made relief maps insist upon the necessity of more or less exaggeration of the vertical scale—generally more than seems to me necessary, however.

An increase of angle of slope accompanies all vertical exaggeration, and this is apparent even in models in which the vertical element is only very slightly exaggerated. It produces a false effect by diminishing the proportionate width of the valleys, and by making the country seem much more rugged and mountainous than it really is. A secondary effect is to make the region represented look very small—all idea of the extent of the country being lost. This can be illustrated better than described. The King model of the United States is an example of one extreme; it is worthy of note that no examples of the other extreme—too little exaggeration—are known.

In small-scale models of large districts some exaggeration of the vertical scale is necessary in order to make the relief apparent, but the amount of this exaggeration is often increased much beyond what is essential. The proportion of scales must depend to a large extent on the character of the country represented, and on the purposes for which the model is made. It has been suggested by a writer, quoted by the Messrs. Harden, that the following exaggeration would afford a pleasing relief: "For a map, scale 6 inches to 1 mile: if mountainous, 1:3; if only hilly, 1:2; if gently undulating, 2:3. For smaller scales, except for very rugged tracts, the exaggeration should be correspondingly increased. For a tract consisting wholly of mountains no exaggeration is necessary." I know of no country of such a character that its relief, in all its detail, cannot be shown upon a scale of 6 inches to 1 mile without any exaggeration at all.

It seems to me that the absolute and not the relative amount of relief is the desideratum, and I have always used this as my guiding principle. For small scale models I have found half an inch of relief ample. It may be worth while to state that in a model of the United States made for the Messrs. Butler, of Philadelphia, the horizontal scale was 77 miles to 1 inch, the vertical scale 40,000 feet to 1 inch, and the proportion of scales as 1 to 10. This proportion could have been brought down as low as 1:6 with advantage. One-fortieth of an inch to a thousand feet seems a very small vertical scale, but it sufficed to show all the important features of the relief. It should be stated, moreover, that the model in question was very hurriedly made—in fact, was hardly more than a sketch-model—and that more care and more minute work would have brought out many details that do not now appear. This amount of care was not considered necessary in this instance, as the model was made to be photographed and published as a photo-engraving, and was to suffer an enormous reduction coming down to five by seven inches.^[2]

It has been frequently urged by the advocates of large exaggeration that the details of a country cannot be shown unless the vertical scale is exaggerated; that hills 200, 300, or even 500 feet high—depending of course upon the scale—flatten out or disappear entirely. This seems plausible, but the advantanges of great exaggeration are more apparent than real. Its effect upon the model has already been mentioned; it should be added that, with the proper amount of care in finishing the model, exceedingly small relief can be so brought out as to be readily seen. With ordinary care, one-fortieth of an inch can be easily shown, and with great care and skill certainly one-eightieth and probably one-hundredth of an inch. Another plausible argument that has been advanced in favor of vertical exaggeration as a principle, is well stated by Mr. A. E. Lehman, of the Pennsylvania Geological Survey, in a paper on "Topographical Models," read before the American Institute of Mining Engineers in 1885. "A perfectly natural expression is of course desired; and to cause this the features of the topography should be distorted and exaggerated in vertical scale just enough to produce the same effect on the beholder or student of the district of country exhibited as his idea of it would be if he were on the real ground itself. Care should be taken, however, not to make the scales so disproportionate as to do violence to mental impressions. Often, indeed, prominent or important features, when they will bear it, may be still more effectively shown by additional exaggeration in the vertical scale." The fallacy of this argument is obvious. It assumes that the object of a model is to show the country as it appears to one passing through it, and not as it really is—and there is often a very wide difference between the two. The impression derived from passing through a country is, if I may use the term, a very large-scale impression, as any one who has tried it can certify; it is certainly a mistake to attempt to reproduce this impression in a small-scale model, with the help of vertical exaggeration. Even if the principle were a good one, its application would be very limited. It could only be used in large-scale models; to apply it to a model of a large area—the United States, for example—is obviously absurd.

The method referred to as being now generally in use may be briefly described as follows: requisites, a good contoured map; a hachured map in addition, if possible; a clear conception on the part of the modeler of the country to be represented; and a fair amount of skill. Materials: a base-board of wood or other suitable material; card-board or wood of the thickness required by the contour interval and the scale; and modeling wax or clay. Procedure reproduce the contours in the wood or other material; mount these upon the base-board in their proper relationship; then fill in the intervening spaces, and the space above the topmost contour, with the modeling material.

In a series of models of the Grand Divisions of the earth, made about a year and a half ago, the contours of card-board were made as follows: the map was photographed up to the required scale, and as many prints were made as there were contour intervals to be represented—in a model of the United States of 1,000 feet contour interval there were fourteen prints. Thirteen of these were mounted upon card-board of the exact thickness required by the vertical scale, and one upon the base-board. All large paper companies use a micrometer gauge, and card-board can easily be obtained of the exact thickness required—even to less than the thousandth part of an inch. The lowest contour was then sawed out upon a scroll saw, and placed upon the corresponding line of the map mounted upon the base-board. This process was repeated with each of the succeeding contours until all were placed and glued into their proper positions. At this stage the model presents the relief in a series of steps, each step representing a rise corresponding to the contour interval. The disadvantages of the method lie in the fact that unless the greatest care is exercised in making the photographic prints there will be considerable distortion, owing to the stretching of the paper in different directions, and consequently much trouble in fitting the contours. If care be exercised in having the grain of the paper run in the same direction in all the prints, trouble in fitting the contours will be much reduced, but the distortion in one direction will remain. In our experience this distortion amounts to about two per cent.; in other words, a model that should be fifty inches long will in reality be fifty-one inches; but, as this error is distributed over the whole fifty inches, it is not too great for an ordinary model. If greater accuracy be required, it can be secured by transferring the contours to the card-board by means of tracing or transfer paper. The great advantage of the photographic method lies in the fact that when the model has been built up, with all the contours in position, it presents a copy of the map itself, with all the details, drainage, etc., in position, instead of blank intervals between the contours. Such details and drainage are a great help in the subsequent modeling.

The next step in the process is to fill in with clay or wax the intervals between the contours. I have always found wax more convenient than clay for this purpose as, unless the surface coating is a thick one, the clay is difficult to keep moist. To obviate this difficulty, some modelers have used clay mixed with glycerine instead of water; this, of course, does not become dry, but the material is, at its best, unsatisfactory. The filling-in process is the most important one in relief map making, for it is here that the modeler must show his knowledge of, and feeling for, topographic forms. Some models seem to have been constructed with the idea that when the contours have been accurately placed the work of the modeller is practically done. This is a great mistake. The card-board contours are only a means of control, occupying somewhat the same relation to the relief map that a core or base of bricks, or a frame of wood, does to other constructions as, for example, an architectural ornament or a bust. It is sometimes necessary to cut away the contour card; for, as has been already explained, a map is more or less generalized, and a contour is frequently carried across a ravine, instead of following it up, as it wonld do if the map were on a larger scale. Such generalizing is of course perfectly proper in a map, but, with the same scale, we expect more detail in a model. The modeler must have judgment enough and skill enough to read between the lines, and to undo the generalizing of the topographer and draughtsman, thus supplying the material omitted from the map.

This can be done without materially affecting the accuracy of the model, considered even as a copy of the contoured map. The contours of card board or other material are, let me repeat, only a means of control. The perfect modeler—a variety, by the way, yet to be evolved—would be able to make an accurate relief map without them, in the same way that other subjects are made; as, for example, a flower panel, an architectural ornament, or any other subject in low relief, where the object sought is artistic effect and great accuracy is not a desideratum. It is the converse of this idea that has produced the numerous models that one sees; accurate enough, perhaps, but wholly expressionless and absolutely without feeling. This is the great fault of nearly all models made by building up the contours in wood and then carving down the shoulders. It is then necessary to sand-paper them, and what little character they might otherwise have had is completely obliterated by the sand-paper. Such models almost invariably look wooden. Let the modeler, then, have a clear conception of his subject and not depend wholly on the contours, and let him work out that conception in his model, "controlled" and helped by the contours, but not bound by them; the resulting model will thus be far more satisfactory and a far better representation of his subject, in other words, it will be more life-like―more nearly true to nature.

The model, provided it be not of clay, is sometimes used in the state in which it is left when finished. It is much more common, however, to make a plaster mould, and from this a plaster cast. For this purpose a moulder is usually called in ; but moulders as a rule are ignorant men, accustomed to one line of work only, and the result is not always satisfactory. It is much better for the modeler himself to do this work, though to obtain good results from plaster it is necessary to know the material thoroughly, and this knowledge comes only from experience. The mould is generally made quite heavy, in order to stand the subsequent hard treatment that it may receive, and should be retouched and thoroughly dried before being prepared for the cast. The method used by some modelers of placing a frame about the model and pouring in the plaster, filling the frame to the top, is a crude and very wasteful one and not at all to be recommended. In a model of large size—say seven or eight feet square—it would require a derrick to move the mould. It is wholly unnecessary, as, with a small amount of care, a good mould can be made not more than an inch thick, or, at most, an inch and a half. The drying of the mould before use can sometimes be dispensed with, but is always desirable.

Nearly all American moulders (as distinguished from French and Italian ones) varnish the mould, and thus lose some of the finest detail and sharpness. This is unnecessary. The mould can be easily prepared with a solution of soap so as to leave nothing on the surface but a very thin coating of oil, which is taken up and replaced by the plaster of the cast. Of course, if the model has been sand-papered, no fine work in moulding or casting is necessary, as there is nothing to save. If the subject is a very intricate one, with "undercuts" (as they are called), it is customary to make a waste mould; as this is very seldom necessary in relief map work, however, the process need not be described.

To make the cast it is only necessary to repeat the processes used in making the mould. With great care and some skill a cast can be produced but little inferior in point of sharpness and detail to the original model. It is customary to make the cast very thick, and, consequently, very heavy; this is unnecessary. In our work we seldom make a cast thicker than one inch, and yet are never troubled with changes in the model after it is finished. Even in a very large cast (now in the National Museum), weighing nearly 1,500 pounds and presenting a surface of over 160 square feet, the average thickness is less than one inch, although it required over five barrels of plaster to make it. The cast, after being thoroughly dried, should be finished—all its imperfections being carefully repaired. The surface, however, should be touched as little as possible, as the slight roughness of surface that comes from the original model, through the mould, is removed by any tooling. This roughness adds much to the effect of the model; in fact, where the scale is large enough, it is sometimes desirable to emphasize it.

The proper way to paint a model is a matter that must rest principally upon the judgment of the modeler, depending to some extent, also, on the use to which the model is to be put. The plain cast is sometimes used, drainage, lettering, etc., being put directly upon it. This has the advantage of preserving all the detail that comes from the mould, but it has also the disadvantage of a surface easily soiled and impossible to clean. If the model is to be photographed, the surface should be nearly white—in our practice we use a small amount of yellow with the white. This yellow is hardly appreciable by the eye, but its effect upon the photographic negative is quite marked. Yellow becomes grey in a photograph, and, in a photograph of a model colored as described, a grey tint is given to the whole surface. The high lights are not pure white, and there is no harsh contrast between light and shade. There is another point of great importance in photographing models: the surface should have a dead finish—that is, should have no gloss, or, at most, should have only what is known among painters as an egg-shell gloss. It is almost impossible satisfactorily to photograph a model that has a shiny surface. Any portion of a model that it is desired to separate from the rest should be painted a different color—the water, for example, should be painted a light blue; not a blue composed of indigo, however, or any of the grey blues, as these produce in the photograph a dead grey, and are not pleasant to the eye. The most satisfactory color that we have used is a mixture of cobalt—the purest of the blues—with Antwerp blue—which is quite green—and white. This gives a color that is pleasant to the eye, has the retreating quality to perfection, and photographs well.

Models intended for exhibition as such should be painted realistically. There is room here for an immense improvement in the usual practice, which is to paint the model either in some conventional scheme of light and shade, or else to put a single flat tint upon it. If the model is to be colored conventionally it is, in my opinion, much better to use a flat tint, light in tone, and with a dead surface. The use of a variety of colors upon the face of a model interferes materially with the relief, especially if the relief is finely modeled. For this reason models colored to indicate geologic formations should always be accompanied by duplicates representing topography only, colored realistically, if possible, and without lettering. Well-defined lines other than those pertaining to the model itself, such, for example, as those used to define the boundaries of geologic formations, should not be allowed upon a model when it is desired to bring out all the relief. The lettering on such models should be kept down as small as possible, or wholly dispensed with. The latter is much the better method.

The cheap reproduction of models is the most important problem connected with the art, and the one that is attracting most attention among those engaged in it; as, until models can be reproduced cheaply, they will never have any wide distribution and there will be far less incentive to the modeler. Various materials have been suggested and experimented on, but nine-tenths of the models that are made to-day are made of plaster of Paris. Although this material was the first to be used for this purpose, it has not yet been superseded. A plaster cast is heavy, expensive and easily injured; but plaster gives an accurate copy of the original, retains permanently the form given it, and is easily finished and repaired. The weight is an obstacle that can be easily overcome. By the incorporation in the plaster of fine tow, or of bagging or netting of various kinds, the cast can be made very light and at the same time strong, but the expense is increased rather than diminished by this method. Models made in this way, however, have the advantage that when broken the pieces do not fall out, they are, however, fully as liable to surface injury as the other kind. The large cast in the National Museum, before referred to, was made in this way. It weighed nearly 2,000 pounds when boxed—not an easy thing to handle—but it stood shipment to New Orleans and back without suffering any material injury. This would hardly have been possible had the cast been made from plaster alone.

Paper seems, at first sight, to be the material best adapted for the reproduction of models; but no one has succeeded well enough with it to bring it into use. Like nearly all those who have given this subject attention, I have experimented with paper, but the only positive result has been a loss of a large part of the confidence that I once had in the suitability of the material. Paper has been used extensively for large scale models of pueblos, ruins, etc., but I have never obtained a satisfactory result with subjects in low relief and fine detail. A paper cast may look well when first made, but it absorbs moisture from the atmosphere, and contracts and expands with the weather. The contraction is apt to flatten out the model and the expansion to make it buckle up.

Casts of models have been made in iron; but this, while suitable perhaps for models of mounds and subjects of like character, would hardly be applicable to small scale models with fine detail; such casts require too much surface finishing. The material known as Lincrusta-Walton seems to me to be the ideal material for this purpose. It is tougher than rubber, will take the finest detail, and its surface can be treated in any way desired. Unfortunately the manufacture of models in this material would require expensive machinery, and is outside the scope of a modeling room. Should it ever become commercially advantageous, however, casts of a model of ordinary size, in every way equal to the original, can be turned out in this material at a very small cost.

It remains to speak of the reproduction of models by process-engravings—a method that will probably receive much more attention in the future than it has in the past. It is perhaps along this line that the cheap reproduction of models will develop; but the subject is too large a one to be adequately treated here, and must be postponed until some future occasion.

Scale, 1 inch - 4 miles

Hachure

Es Contour- 200 ft. interval 500 ft. Scale, 1 inch = 1 mile Hachure. Contour-interval: 40 ft. Contour-interval: 80 ft. Contour-interval: 120 ft.

HACHURED AND CONTOURED MAPS

REPRESENTATION OF A HILL ACCORDING TO THE TWO SYSTEMS AND ON DIFFERENT SCALES.

From Supplement to Enthoffer's Topographical Atlas by permission of Mr. Enthoffer.

FROM BUTLER'S COMPLETE GEOGRAPHY.

Copyright, 1888, By E. H. Butler & Co.

Printed by permission.

1. For specimens of representation of the same subject on different scales, in both the hachure and contour systems, see plate from "Enthoffer's Topographical Atlas."
2. See plate from "Butler's Complete Geography."