A BOY’S SOLAR MICROSCOPE.
The microscope is, as every boy knows, an optical instrument, which enables us to see and examine objects which are too small to be seen by the naked eye. The arrangement of the solar microscope is similar to that of the magic lantern, the sun taking the place of the limelight usually employed. In this form of the magic lantern, two difficulties are to be overcome; one, the necessarily fixed position of the instrument; and the other, the very inconvenient habit the sun has of constantly changing his position; so that it would be impossible to adjust the lens without the aid of a mirror, to throw sufficient light in upon the object to be examined. Both of these obstacles are surmounted in the simple arrangement of the solar microscope here described.
First make a strong frame of wood, seven-eighths of an inch in thickness, that will exactly fit in the lower half of the window when the sash is thrown up; and in the middle of this fit an upright board a foot wide, which has a hole cut in its center ten inches in diameter. Fasten it strongly in place by four nails driven through the frame, and well into the ends of the boards, or, if more convenient, by long screws inserted in the same places. Fig. 1 shows the position of the board a, also that of the nails b. The open spaces, c, are to be closed by several thicknesses of brown paper pasted or tacked across on the inside of the frame. The upper part of the window must also be closed, so that no ray of light shall enter the room, except through the hole d.
Before proceeding further, it may be well to remark, that, as perhaps the largest part of the work is the cutting of no less than seven circular holes of various sizes, through as many pieces of board, a scroll-saw will be found an almost indispensable aid to the construction of this apparatus. Also, that the window in which this microscope is used must necessarily have a southern exposure.
In Fig. 2 we have a disk of half-inch wood, twelve inches in diameter, with an opening in the center four inches across, to hold the condensing lens, a; b is a mirror five inches wide and ten inches long, turning on an axis which passes through the supports, c c, the latter being attached to the disk. These supports should be long enough to admit of the mirror turning entirely around without touching the disk, and are fastened in place by screws passing through the disk and into their ends. When the mirror is in place, cut the slit d parallel with the edge of the mirror, for the wire e to pass through. The manner of attaching the wire to the back of the mirror is seen in Fig. 3. The back is first covered with paper to prevent its scratching; then the wire is bent and laid in place, and lastly, a piece of very strong paper is pasted over the wire and entire back, and caught down over the edge of the front, forming a narrow frame to the glass; the ends of this wire should pass through rather small holes in c c, so that it will not turn easily out of position. A handle (see f, Fig. 4) should be placed on the other side of the disk, and just across the lens from the slit d.
Next take two pieces of wood, fifteen inches square and half an inch thick; in the center of one cut a hole twelve inches in diameter, while in that of the other cut another round hole only ten inches across. In Fig. 4, which represents a section of this microscope, g is the central board of the screen, marked a in Fig. 1; h is the piece you have just made, with the central opening twelve inches in diameter; and i is the second piece, which measures fifteen inches square, but has a hole of only ten inches diameter in its center; d, which has a dotted surface, to distinguish it from the frame-work, is the large disk (Fig. 2), which, you remember, is just twelve inches in diameter, and, consequently, will exactly fit the opening in h; if these edges are rough, sand-paper both with a coarse quality first, finishing them off with a finer kind. When d is in position, and moves easily but not loosely in h, place i over it and fasten it in place with screws, passing through i into h; but h, of course, must first be strongly nailed or screwed upon g.
You will now see that by turning the handle, f, the position of the mirror, which is fastened to this disk, can be easily changed so that it shall face in any direction, while by drawing the wire, e, it can be turned so as to reflect the sun’s rays through the lens, a, from whatever quarter of the heavens it may be shining. This double adjustment of the mirror and lens enables you to throw the rays of the sun through the opening in upon the object, o, at any hour of the day. As the mirror is adjusted in Fig. 4, the sun must be very low, as its rays, to strike the mirror, would necessarily be nearly horizontal.
The lens, a, should be held in place by two pieces of whalebone, bent around on either side of it, at the edge of the opening in d; this lens is four inches in diameter, and has a focal length of nine or ten inches; its adjustment had better be left till everything else in the microscope has been finished. Fig. 5 shows the appearance of this when completed.
As the outer part of the work is fitted, we will now turn our attention to the other, or inner, side of the screen. In Fig. 4, the board j is eighteen inches long by ten inches wide, and half-an-inch thick. In the middle is a small circular hole, one and one-half inches in diameter. This is fastened to the middle board, g, by the four horizontal posts, p, each six inches long.
Now take a square piece of half-inch board, five inches across, cut a circular hole two inches in diameter in the middle, and fit into this hole a pasteboard tube four inches long, which is painted black on the inside. The edge of the circular hole in j should also be black. In Fig. 6, which represents this board, you will notice two cleats, l l, fastened to the back of k; these are also made of half-inch wood, and are five inches long by one wide. In Fig. 4, the position of k and l is seen in connection with the longer piece, j; the center of the openings in j and k should form one and the same horizontal line. The opening between l and l is for the glass slides upon which the objects to be examined are placed.
After these parts are fastened in their proper places, make a pasteboard tube, with a black inner surface, as represented at n, about four inches in length, and inclose in one end two lenses, each one and one-half inches in diameter, and each having a focal length of four inches. Fit this tube in the one marked m. Now, having everything in place, fit in the lens, a, so that it will send the rays of light directly through the hole in j upon the object in l, and fasten it securely in place with your bent whalebones.
The screen upon which the image is thrown can be the opposite whitewashed surface of the room, if by a proper adjustment of the tubes the image can be made distinct, or it can be a sheet stretched over a frame-work of light wood; the latter is preferable, as it can be more easily brought in focus. Of course, in this form, as in any other “magic lantern,” the nearer the screen to the lantern, the longer the tubes m n; but the image, which is smaller, gains in brilliancy of illumination, while with these conditions reversed, the results are the opposite; a larger image, but less bright in appearance. The same light being spread over a larger surface is necessarily less strong.
SOME OBJECTS FOR THIS MICROSCOPE.
The objects which can be examined by aid of this instrument are many in number, and can be readily prepared by simply inserting them between two pieces of glass, sufficiently small to slide in the opening l l, and pasting bits of brown paper over the edges to hold them in place.
In this manner the legs of flies and mosquitoes, the heads of the latter with their venomous sting; hairs of the dog and cat, also from the human head; tiny sections of human skin; down from the butterfly’s wing, obtained by dusting off a few of the tiny particles upon a glass plate; the pollen from different flowers; spores of the puff-ball and tiny grains of dust, all make very interesting subjects for study, when magnified and thrown upon the screen in the darkened room.
One of the most interesting experiments with this form of the magic lantern is made by throwing the image of a drop of some solution, like sulphate of copper, upon the screen, and watching the process of its crystallization; sulphate of copper and of iron; hyposulphite of soda, which latter may be colored by adding a very little permanganate of potash to the solution.
The eels in a drop of vinegar, drops of stagnant water, and the larvæ of the mosquito are also interesting objects, when viewed by the aid of this powerful magnifier.
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