Harper's indoor book for boys

by Joseph H. Adams

Through the top hole a lamp-chimney may project that the surplus heat may be carried upward. For the side opening a sheet-iron door should be made and hung in place with small brass hinges, and a brass lever catch to keep it closed.

This catch is a simple little affair, and consists of a thin piece of spring brass, in one end of which a hole has been made, while at the other a little knob handle is riveted. One end is attached to the door, and to the hood beside the door a catch of thin brass is riveted fast, into which the lever catch can drop.

To stiffen the door, the edges should be bound with narrow brass strips, securely fastened with small rivets, or escutcheon pins, that can be adapted as rivets by cutting them to the required length.

Two runners half an inch wide and three-eighths of an inch in thickness are to be screwed fast to the uncovered top of the base-board, four and a half inches apart, as shown in Fig. 11. From sheet-iron cut two strips half an inch in width and ten inches long, and fasten a piece to the top of each runner, using the same screens to hold them in place that secure the runners to the base-board. One-eighth of an inch of each strip will project over the inner edges of the runners, as shown in Fig. 12, and this edge will serve to hold the wooden slide-holder and objective-lens board in the proper position on the base-board.

Make a sheet-iron door six inches wide and seven inches high, with the edges rolled over a wire to stiffen them, and in the bottom of the door, at the centre, cut an opening half an inch wide and two inches high. This will allow the door to be closed over a gas-pipe that may project for a short distance from the rear of the enclosure. Attach this door to the back of the hood with two small hinges riveted at the top, as shown in Fig. 13, and across the under side of the base-board, and two inches from either end, screw battens of wood in which pins have been set. These battens will raise the lantern up from a table or box on which it may rest, and allow a draught to pass up through holes made in the base-board inside the enclosure formed by the iron hood. These draught-holes will be necessary for either oil or gas light, and they can be bored about as shown in Fig. 13.

Two small wooden runners must be fastened to the base inside the enclosure, a distance of four and a half inches apart, and between them a lamp or gas-jet tray will slide.

From the thin mahogany cut three pieces four and a half inches wide and seven inches long. In the middle of these, and four inches from one end, make a centre dot, and with a compass-saw cut a hole in one of them three and a half inches in diameter, and in another cut a hole three and a half inches square.

In the third board make a hole the diameter of the objective lens; then with screws and glue fasten the first two boards together, as shown in Fig. 14 A, so that a space of three-quarters of an inch will remain between them. The height of this opening should be four and a quarter inches, and the holes in the middle of the boards should be centred. These two boards and separation blocks are to be fastened in an upright position to a narrow piece of three-eighth-inch board the same length as the width of the upright boards, as shown in Fig. 14 A; and at the outer edges a saw-cut at the joint will allow this frame to slide back and forth between the runners, so that the iron edge may fit in the saw-cut.

To the inside of the front board two springs should be attached with screws at one end of each; these springs may be shaped from corset steels, and they should be bent in a curved position, as shown at the lower end of the opening in Fig. 14 A. Their use is to hold the slide-carrier back against the rear board and firmly in place. Slide-carriers may be purchased at an optical supply house, and they are made in several shapes; the most convenient ones, however, are the sliding wooden holders that accommodate two slides.

The remaining board is to be mounted on a block and held in place by two angle strips, as shown in Fig. 14 B; and to enable it to slide between the runners it should receive saw-cuts also. Procure a camera-bellows four inches square, or in its absence employ a piece of black silk or gossamer cloth, and attach it to the frames, as shown in Fig. 16, with small curtain tacks and glue. Having mounted these boards on the base-board between the runners, the box is then ready to receive the lenses and lamp.