[Fig. 219] L is a steel wire spring (a window-shade spring will 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.]
Home-made cabin door-locks.
