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