Page:The American Boy's Handy Book edition 1.djvu/283

will be thrown upon the paper and show through, so that they can be painted upon the opposite side of the paper without any danger of moving either the light or plants.

At most of the artists' material stores in New York there is to be found for sale a sensitive paper which changes color when exposed to the light. If a shadow be cast upon this paper by some object between it and the sunlight, the paper will grow lighter in color all around the shadow, and in a few moments the shadow is marked distinctly by the difference in tints. At this stage the paper, which is of a dark blue color, may be removed, and if it be held under a stream of water the parts that were covered by the shadow will become white and remain so. I have before me a photograph of a large dragon-fly, which shows all the beautiful network of veins in the wings of that insect traced in the most delicate white lines upon a background of dark blue. I allowed the dragon-fly to rest for a few moments upon a piece of sensitive paper and then quickly placed the paper under a hydrant, with the result described.

Photographic paper is not expensive, quite a large sized sheet costing only fifty cents. Many pretty experiments can be tried with this material.

Suppose you have a picture of a horse and want to enlarge it. First draw a line under its feet, and at right angles with this line draw another line in front of the horse's head; divide these lines into equal parts and then carefully rule lines across from these points so as to intersect each other at right angles, as illustrated by Fig. 163. When the horse is all enclosed in squares, take another piece of paper and make exactly the same number of large squares on the paper as there are smaller ones on the horse picture; number the squares on both as in