TopograjpTiic Models. 263 



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 great- 

 est 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 coat- 

 ing is a thick one, the clay is diflicult to keep moist. To obviate 

 this difiiculty, 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, topo- 

 graphic 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 con- 

 structions 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 



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