BY F. CHASEMORE.
For this, get a wooden tooth-powder box, plain--that is, without
projecting rims--take off the lid, and smooth it all over. Next make the
compass-card. Cut this circular, about a quarter of an inch smaller than
the inside of the box, which should be about two inches and
three-quarters in diameter outside. Mark the centre of the card, and
mark from this centre the thirty-two points of the compass (as Fig. 1).
Now make the needle. This must be hard steel; you can get this at the
tinman’s or ironmonger’s. Get him to cut it about two inches long and
three-eighths of an inch wide in the middle, tapering to a point at each
end. The steel should be about a sixteenth of an inch thick. Get him to
drill a hole through the middle of this steel about an eighth of an inch
in diameter. Get a small piece of brass wire a quarter of an inch in
diameter and a quarter of an inch long. File a shoulder to this (as Fig.
2) about a sixteenth of an inch wide and an eighth of an inch from the
end. Drill a hole triangular in section an eighth of an inch deep and
about an eighth of an inch at the outside. Place this through the
compass-card. Now magnetize your needle. This is done as follows.
[Illustration: Fig. 1.]
[Illustration: Fig. 2.]
[Illustration: 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.
[Illustration: Fig. 4.]