Fig. 2.
Fig. 3.
Get a magnet—most boys have one—and draw one end of it from end to end of the needle, always going the same way and never back again. Do this about twenty times and your steel needle will be a permanent magnet. Now place this underneath the compass-card and push the little brass button through the hole in it. Suspend this by placing a point in the hole in the brass stud, and one end of the needle will point towards the north. Mark this point, and turn the card on the stud till that end of the needle points to eighteen and a half degrees west of the north point on the card. Now fasten the brass in the needle by two or three taps with a hammer on the under side of the brass, being careful not to strike the steel. Next fix it more securely with a dot of sealing-wax on each point and card. Now suspend it again on the point, and the north point will dip towards the earth. You must balance the card by putting dots of sealing-wax here and there till it swings quite level.
Next, in the centre of the bottom of your box fix a steel pin about half an inch high, brought to a point that will go loosely in the dent in the brass stud. Put your card on this point and it will swing easily in the box. Line the box with a strip of cardboard a little wider than the height of the top of the brass stud from the bottom of the box. Get a circular glass the size of the inside of the box (your glazier will cut this for you for a few pence). Put it on the shelf formed by the cardboard, which should be glued into the box, and fasten it in its place with a narrow strip of cardboard glued in all round the box.
By putting the glass in you can turn the box about any way in your pocket without the card coming off the peg.
Now to make the timepiece. Make a dial plate of paper the size of the top of the lid. You can first draw this on a sheet of paper, and then placing one leg of a pair of compasses on a point in the twelve-o’clock line—which must in this case be only one line, about half an inch from the six-o’clock line—mark a circle the exact size of the top of the lid. Inside this circle make another about a quarter of an inch from it, and mark the hours inside this circle. Paste this paper on the top of the lid, and put the lid on the box. Now draw a line from the twelve-o’clock line on the lid right down the side of the box; make this line quite perpendicular to the top and bottom. Now make the gnomon. Get a piece of very thin sheet brass or tin-plate about the thickness of a card and cut the gnomon out of it. The shape and size can be got from directions already given. Now with a thin, fine saw, cut the twelve-o’clock line into a slot about a sixteenth of an inch deep and going beyond the six-o’clock line a little, about an eighth of an inch. This slot must be the same depth in the six-o’clock end as at the edge of the lid. You can push the base of the gnomon into this slot, so that the axis edge exactly crosses the six-o’clock line.
To use the compass, take off the lid, place the box level, and note where the north points, and you can determine any point of the compass from that. To use the timepiece, set the box level, and bring the mark in the side of the box to correspond exactly with the north point of the card. Put the gnomon in the slot in the lid, and put the lid on the box without disturbing it, so that the mark in the side of the lid corresponds exactly with the mark in the side of the box, and the shadow of the axis of the gnomon will point out the hour. When you have seen the time, take off the lid, take the gnomon out of the slot, and put it inside the box, laying on the glass, and put the lid on. You can thus carry the whole in your pocket without a fear of it getting out of order; and when you are out for a walk, and the sun shines, you can always tell your way home and the time to go there.
