Page:The wonders of optics (1869).djvu/227

 latter the greater will be the distortion of the drawing Now draw the lines 1,  2,  3, and  4, and join to a. Wherever a crosses the divisions 1, 2, e 3, 4, and b, draw a horizontal line, parallel of course with a b. You will thus have a trapezium a b c d divided into as many spaces as the square in fig. 62, and it now remains to fill them in with similar portions of the figure. Thus, for instance, the nose is in the fourth vertical division, starting from the left, and in the third and fourth counting from the top; in order, therefore, to make it occupy so lengthened a space it must be considerably distorted by the pencil. It will be readily seen also that the more numerous the spaces into which the square is divided, the easier it will be to draw the distorted picture. It is by this means that the anamorphosis shown in fig. 63 has been drawn.

The next thing to do is to find the point of view from which we can see the figure in its natural proportions. This will be found to be at a distance above the point equal to the line. In order to complete the experiment it is simply necessary to place the distorted picture in a horizontal position, and fix a piece of cardboard vertically at the point. If a hole be punched in it at a distance from equal to, and the drawing be looked at through it, the whole of the parts will fall into symmetry immediately.

The experiment may be tried first with fig. 63, the hole being made rather large, and the eye placed at a distance of from 3 to 4 inches.

It would be difficult, without having recourse to geometrical formulæ, to explain how it happens that by placing the eye at a particular point the distorted lines of the drawing become symmetrical; but perhaps a mechanical demonstration will help to make this difficult subject a little plainer.