ll answer the
purpose), fastened to the door at one end and to the latch at the other
end, and serves to keep the latch down and in place when locked.

Fig. 219 _K_ is the latch-string, one end of which is fastened to one end
of the latch and the other end run through a hole near the top of the door
and extending outside the same as the latch-string (Fig. 218).

Fig. 219 shows the positions of the latch and key when the latch is
locked; to open the lock from the outside it is necessary to pull the key
string first (_H_, Fig. 220), which releases the key; then pull the
latch-string, thus lifting the latch while still holding the key string.
The key string is now let go; the spring forcing the key into the position
shown in Fig. 221 will keep the door unlocked.

When leaving the room, all that is necessary is to pull the key string
which lifts the key, then let go the latch-string, and the latch will
spring back to its locked position and the key will also fly back into its
position as in Fig. 219. Any one not knowing the combination will be
unable to open the door.

Fig. 218. Fig. 219. Fig. 220. Fig. 221. Fig. 222. Fig. 223.

Fig. 224. Fig. 225. Fig. 226. Fig. 227. Fig. 228.

[Illustration: Home-made cabin door-locks.]

The Compass Lock

This lock is made on the same principle as the combination safe lock, but
it is a lock any bright boy can make for himself. In the first place,
instead of numbers, use compass divisions; that is, use a disk with the
points of the compass scratched on it and an ordinary door-knob with an
index mark filed on its base, as shown by Fig. 224 where the finger is
pointing.

Hunt up three old door-knobs like those shown in Figs. 222, 224, and 225.
When you take one of the door-knobs off one end of the shaft you will find
several small screw holes in the steel shaft (Fig. 222). Over this end you
set a block of hardwood which you fashion out of a square block (Fig. 223)
by first cutting off the corners as shown by the dotted lines, then
whittling the angles off until it becomes rounded like a compass face;
after which saw off an arc, that is, part of a circle, as shown in Figs.
224, 226, and 227. Next make a square hole through the centre of the
circle to fit the square end of the steel shaft of the door-knob. The
square hole is not the centre of the block as it is now cut, but it is the
centre of the block as it was when it was round; that is, the centre of
the circle. Insert the squa