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Description |
| The sand table is simply a box mounted on trestles to a convenient height, or a curbed table, partially filled with sand. On such a table a piece of terrain is represented in miniature to any desired scale, by moulding the ground forms in moistened sand - the hills, valleys, etc. It is thus a form of relief map. (Plate 10.) |
| The effect of realism on a sand table terrain is limited only by the imagination and ingenuity of those preparing it. Woods and standing crops may be represented by the use of color (green or yellow), in the form of paint or kalsomine power or ground chalk, sifted on with a piece of wire netting or a salt cellar [sic: shaker]. Small streams are represented by blue coloring, larger streams, ponds, and lakes by bits of glass, isinglass, celluloid, tin or small mirrors, imbedded in the sand. Tree masses are represented by sifting loose sand upon the finished surface to the proper height, and coloring it green. |
| Roads and railroads may be traced with a roller or stylus. A corrugated roller may be made to simulate the ties of a railroad. Roads may be colored yellow or brown. Buildings of all kinds, bridges and other artificial features, may be fashioned from bits of wood and colored with ink or crayons. |
| Furnishings. Sets of miniature furnishings to heighten the realistic effect of the sand table have been prepared. Some of these are for sale. Undoubtedly they tend to make the instruction more entertaining and therefore usually more valuable. But it is necessary to have a care that, regarded as toys, these devices do not unduly distract the attention of the student from the real purpose. So far as the present course is concerned this purpose is not the making of toy landscapes, but the teaching of the technique of tactics. Such equipment, while perhaps desirable, is by no means essential, and an entirely satisfactory representation of the terrain may be prepared with no materials other than sand, powdered paint, bits of glass or isinglass, and wood, matches, etc. all of which are easily obtained in any locality. A photograph of a well-prepared sand table might easily be mistaken for that of an actual terrain by a not too critical observer. |
| The sand table is an interesting device and a most excellent means of practical indoor instruction in many subjects, both civil and military. Its value in making the course both more entertaining and more profitable should not be overlooked. Every institution or organization which seriously endeavors to teach the art of war, should provide sand tables for instructional purposes. |
| The advantages of the sand table over other forms of relief map for tactical instruction are several: |
| 1. It is cheaper and simpler. Anybody can make a sand table in a short time with little expense. Therefore, it will often be available when more expensive types cannot be made or secured. This fact has a most important bearing on the war training of large numbers of officers and non-commissioned officers. At the instruction camps sand tables may be made in large numbers when other forms of relief map would be out of the question. Former members of the R.O.T.C. who will be used as instructors will be familiar with sand table methods of instruction. |
| 2. Any desired terrain can be quickly reproduced. |
| 3. Any scale of reproduction desired at any time, for any purpose, can be used, and any relation between horizontal and vertical scales. |
| 4. The sand table simulates actual terrain more closely than a relief map of any other material. |
| The advantages of the sand table over the topographical map are: |
| 1. The student is not required to devote a large part of his attention to reading the map. Map reading is certainly of importance, but in this case we are teaching tactics. |
| 2. On the sand table it is always possible to prepare the terrain exactly as wanted to bring out certain principles. On any other form of map it is usually necessary to adapt the problem to the map to some extent. |
| 3. The sand table can use any scale. In particular it can use a larger scale than any map. |
| Dimensions. The sand table may be made in any size or shape, according to the purpose for which it is to be used, and the floor space available. A convenient size for instruction in tactics is 10 feet x 3 1/2 feet or 10 feet x 4 feet. The depth of the curb is from 1 to 2 feet, and the height above the floor should be the same as that of an ordinary table. (Fig. 1, Plate 10.) |
| Equipment required. The box is a little more than half-filled with fine sand. It is well to add a little clay to the sand, so that when moistened it will be more easy to mould and will retain its shape for a reasonable time. Do not add too much clay as this will cause the model to harden and crack. Moulders' sand is suitable if it can be obtained, but any sand will answer. |
| The equipment necessary to make up the sand table includes: |
| 1. About a barrel of sand, more or less according to size of table. |
| 2. Powdered paint, kalsomine or chalk - green, yellow, blue, and other colors as desired. |
| 3. Some pieces of glass, isinglass, celluloid or bright tin, to represent water. |
| 4. Some pieces of linen backed paper, about 12 inches square |
| 5. A hardwood straight-edge long enough to reach across the table. |
| 6. About 60 grade stakes, 1/2 to 3/4 inch square, sharpened at one end, half 3 to 4 inches long, half 6 inches long. |
| 7. A ruler 1 foot or 15 inches long, graduated in tenths of an inch, or centimeters; or a piece of straight hardwood of the same size on which graduations may be marked. |
| 8. Thumb or carpet tacks. Twine. |
| 9. Miniature houses and bridges may be made of wood with a pocket knife and colored with ink or crayon. |
| 10. Other miniature furnishings as desired. |
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To Reproduce on the Sand Table a Piece of Terrain from a Contoured Map |
| The sand table has a fixed size. Accordingly, the scale of the sand table terrain will depend on the actual size of the area represented as compared with the fixed area of the sand table. It is not necessary that this scale be exact, that is, 100 to 1 for example. It may be made exact if desired, but 98 to 1or 103 to 1 will answer as well. It is, however, evidently necessary that the terrain to be represented have the same shape and proportions as the sand table. The sand table is a rectangle whose sides are in the proportion of say, 3 and 1/2 to 10. Therefore the terrain to be reproduced must also be a rectangle with sides in the proportion of 3 and 1/2 to 10. |
| If it is desired that the scale of the sand table shall be, for example, ten times that of the map, construct a rectangle (of paper or tracing cloth) whose sides are 1/10 those of the sand table, or 0.35 foot by 1.0 foot. Lay the tracing cloth over the map, and shift it about until the rectangle covers the area it is desired to reproduce. Construct on the map area, or on the tracing cloth, a grid of squares (see Plate 10). It is better to divide the long dimension of the area into 10 equal parts and its short dimension into 3 and 1/2, as the squares will then correspond to one foot squares on the sand table. But if the terrain is very diversified or an accurate reproduction is desired, 9-inch or 6-inch squares may be used. Anything smaller than this will waste time. The long lines are marked as A, B, C, (etc.), and the short lines 1, 2 ,3 up to 10 (or more, if smaller squares are used). The intersections or corners of the squares will then be designated as A1, B1, C1; A2, B2, C2, etc. Elevations along the edges of the map may also be taken. |
| A grid for the sand table, corresponding to that of the map, is then constructed. The edges of the table are graduated in feet. A piece of string is stretched parallel to the long edge and one foot from it, a second string one foot from the first, etc. (A-A, B-B and C-C, Fig. 1, Plate 10). The numbered lines of the grid are made by laying a straight-edge parallel to the short dimension of the table. (Fig. 1, Plate 10.) |
| It is convenient to take the contour interval of the table as one inch (or one centimeter) or some multiple thereof (2 or 3 inches) according to the relative scales of the map and the sand table, and the amount of relief it is desired to show. The vertical scale should always be exaggerated as otherwise the terrain will appear too flat. |
| Taking now the map grid, note and record the elevation of each intersection. This is readily done by interpolating between contours to the nearest foot. Thus the intersection B-3 (Fig. 1) is about 0.8 of the distance from the 520-foot contour to the 530-foot contour. Hence, its elevation is about 528 feet. Having recorded the elevations as in the table following, it is noted that all of them are above 500 feet. Hence, we may subtract 500 feet from all readings. If we now divide the results by 10 we have the number of contour intervals that each point is above 500. Columns 2 of the table give the actual elevations. Columns 3 give these elevations reduced to contour intervals above 500. |
| (Total of elevations, 82.0. Average elevation (82/27=3.0). |
| If we take 1 inch as the contour interval of the sand table we thus have the elevations in inches of all points of the sand table terrain above the assumed zero (Columns 2). If the contour interval for the table is to be 2 inches, these must be multiplied by 2, etc. |
| The average elevation of the terrain to be reproduced should be the same as the average height of the sand in the table. Otherwise it will be necessary to add sand to or remove it from the table, though there is no grave objection to this. To obtain the average elevation of the sand, level off the sand on the table. To obtain the average elevation of the terrain to be represented, add the elevations in Columns 2 of the foregoing table and take their average (divide by 27-the total number, and take the nearest whole number). This is found to be 3.0. Therefore the No. 3 contour should be at the height of the levelled off sand. Ordinarily it will be sufficient to take the middle contour as the average height of the terrain. Thus, in the case shown in the figure the contours run from 500 to 540 and 520 may be taken as the average. It may be necessary to add or remove a little sand. |
| Suppose the level of the sand to be any number of inches below the top of the curb around the table, for example, 6 inches (take the nearest even inch), and that the assumed contour interval is 1 inch. Then the No. 3 contour should be 6 inches below the upper edge of the curb (or the bottom of the straight edge when laid on the curb). The No. 2 contour will be 7 inches below the curb, the No. 4 contour 5 inches below (Fig. 3 Plate 10). We may thus formulate a simple rule for this particular case: To find the distance in inches from the bottom of the straight-edge to any contour, or any intermediate point between contours, subtract the elevation of the point as given in the preceding table (Column 2) from 9 inches. These results are given in Columns 3 of the preceding table. A like simple rule may be formulated for any other conditions. Thus, if the level of the sand were 7 inches below the top of the curb, and at the level of the No. 5 contour, the tabular elevations would be subtracted from 7 plus 5, or 12 inches, to give the distance from the straight-edge to the point in question. Fractional parts of an inch should not be used. Take the elevation of the sand to the nearest inch for this determination. |
| The foregoing table having been prepared we are now ready to reproduce the terrain on the sand table. The sand is moistened and roughly leveled off, the strings stretched, as heretofore described and shown in Plate 10. Lay the straight-edge successively on the lines 1-1, 2-2, 3-3, etc. (Fig. 1). The intersections of the straight-edge with the strings will be the points A-1, B-1, C-1; A-2, B-2, C-2, etc. The figure shows the straight-edge on the line 3-3. Take a grade stake of appropriate length and stick it into the sand exactly below the point A-3, indicated by the intersection of the straight-edge and the third string. From Column 3 of the preceding table we see that this point is 4.1 inches below the curb. Push the stake down with the ruler until it is in its proper position, reading the ruler at the bottom of the straight-edge. (Fig. 3) Proceed in like manner to set stakes at each intersection. |
| Another method, which some may find simpler, is as follows: Prepare a table or grid showing the map evaluations at each intersection. Note the average height or middle contour. Place a grade stake (anywhere on the table) approximately at the height of the leveled sand. Lay the long straight-edge across the table above the stake. With a short plain piece of wood measure the distance from the bottom of the straight-edge to the top of the stake. Mark this with the reference of the middle contour. Lay off contour intervals in both directions (up and down) and divide into tenths (or twentieths if the map interval is 20 feet). The highest contour should be near the bottom of the stick, the lowest contour above. Each grade stake is now pushed down until the bottom of the horizontal straight-edge is opposite the proper map reading on the stick. |
| In addition to the grade stakes at the intersections, stakes may be set at critical points within the squares, such as hill-tops, if this considered necessary. |
| When the grade stakes are set some will be below the level of the sand, others will project above. An assistant scrapes away the sand which is above the stakes, and heaps it up about the stakes which project above the sand level. |
| When all the grade or elevation stakes have been placed, remove the strings and straight-edge. With the hands finish scraping away the sand from the stakes which are below the original level, and heaping it up about those which are above, being careful not to move the page. If necessary add or remove sand, until at each grade stake or peg the sand is just level with the top thereof. Now take the map, and using it as a guide mould the sand between the stakes until it conforms to the contour indicated by the map, as nearly as may be judged by the eye. Smooth the surface of the sand by rolling it with a bottle, and by laying the linen backed cloth upon it and rubbing with the hand. |
| Using the gridded map as a guide, and the grade stakes as reference points, trace the streams and roads, the outlines of wooded areas, etc., and locate such important features as towns, large-buildings, etc. When this has been done push the grade stakes down into the sand. |
| The map should now be dressed up or furnished to give it a realistic appearance. Streams may be represented by strips of glass, etc., their edges covered with sand, or by a trail of blue powder (paint, kalsomine or chalk). Sprinkle loose sand by handsful over the wooded areas, to give them the rough, irregular appearances of woods as seen from the air, and color with green powder. Roads are traced by using a specially prepared roller, or a circular object such as an inkwell cover, or with a wood to represent houses and bridges, where shown on the map. |
| Number of tables required. For the solution of problems a sand table 10 x 4 feet in size will answer for 12 to 15 students. For convenience, especially for writing, a shelf about 1 foot wide may be place around the table just outside of and flush with the top of the curb. |
| For demonstration purposes one table may be made to serve for a large number of students by placing elevated seats (like baseball bleachers) on one or more sides. |
| Where ample floor space is available tables of larger size may be used, especially for instruction in field fortification. |