After your collection is complete, and all are dry, they will be much improved by bleaching. This process is also very simple, consisting, as it does, of merely dipping them in a weak solution of chloride of lime, and letting them remain there until the proper color is attained; then by slipping a piece of unglazed paper—ribbon paper is best for this purpose—beneath the surface of the water, and bringing it up with the leaf lying flat upon it, the skeleton can easily be taken from the water.
If the form is not inclined to spread out on the paper as it should, take a long slender darning-needle, and with the point carefully arrange it to your satisfaction. Another drying is now necessary, but the bleached leaves should be left on the ribbon paper, which may be put between the leaves of a book as before.
These can be kept for years, and should you be successful and obtain a number of perfect specimens, they will form a very valuable addition to your materials for Christmas gifts, and, prettily arranged, a very acceptable present to any dear friend.
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CAMERA OBSCURA.
Camera Obscura, a Latin name, meaning literally a dark chamber, belongs to an instrument invented by Baptista Porta in the sixteenth century.
The principle involved in the simplest and most refined forms is the same, and may be illustrated by the following experiment: Let a small hole be cut in an opaque window-shade, and the room darkened. If, now, the beam of light entering the room by this hole be intercepted by a sheet of white paper, held at a small distance from the hole, an inverted image of objects without will be seen upon the paper. By placing a small convex lens over the hole this image is rendered much more distinct. It will also be found, that at a certain distance from the hole the image attains the sharpest or clearest outline, and that if the paper be removed from this point to any position either nearer to the hole or further from it, the image becomes indistinct and confused. At the point of greatest clearness the image is said to be focused. Such being the principle of the camera, it is evident that in practice the instrument may assume many forms, provided always that it consists of a darkened box or chamber, having a hole at one end for the insertion of a lens or combination of lenses, and at the other a screen, generally made of ground glass, on which to receive the image. One of the first home-made cameras I remember seeing was constructed by a boy friend many years ago. In it he used a lens from an old ship’s spy-glass, which still remained incased in its brass tube. Fig. 1 gives a view of this form of camera. As every boy is not as fortunate as my friend in having a brass mounting for his lens, it would be well to inclose it in a small tube of papier-maché or pasteboard, so that it may be moved in or out of the opening at will. The box itself was made of cigar-box wood, with the cover sawed in two parts. After the hole had been cut at one end and the lens inserted, a piece of looking-glass was placed obliquely across the lower corner of the other end of the box, the longer piece of the cover nailed on the front part of the top, and a piece of ground glass carefully fitted, with the ground side downward, over the remaining open space; the smaller part of the cover was then fastened on one side with small pieces of tape. When not in use, this little cover fell down over the glass, but when any object was to be viewed the little lid was lifted into the position in the cut, and served as a shield to the ground glass beneath. A piece of black cloth thrown over this cover, and allowed to fall over the triangular side-openings, so as to still further prevent outside light from reaching the ground glass, is a great improvement.
In the diagram, the dotted lines show the course of the light from the object in view, through the lens (where the rays cross each other) to the looking-glass, and thence to the ground glass above.