Two guards, _A_ and _B_ (Fig. 208), made as in Fig. 216, protect the bolts
and act as guides to keep them from swinging out of position; two springs
_C_ and _D_ (Fig. 208), made of well-seasoned hickory and attached to the
battens on the door by nails or screws, force the bolts down and up into
the bolt-holes (Fig. 208). To release the bolts, the spring must be drawn
back as shown by the dotted lines in Fig. 208. This may be done by means
of a string or picture wire, which is fastened in the ends of the bolts
and runs through a hole in the ends of the spring and is attached to the
lever _E_ (Fig. 208). When the end of this lever is pushed down into the
position shown by the dotted line and arrow-point, it lifts up the Hall
bolt at the bottom of the door and pulls down the Billy bolt overhead,
thus unfastening the door.
Fig. 208. Fig. 209. Fig. 210. Fig. 211. Fig. 212. Fig. 213.
Fig. 214. Fig. 215. Fig. 216. Fig. 217.
[Illustration: Jack-knife latches suitable for Canada and America.]
But, of course, if one is outside the door one cannot reach the lever _E_;
so, to overcome this difficulty, a hole is bored through the central
batten of the door and the latch-string is tied to the top end of the
lever and the other end is run through the hole bored in the door (Fig.
208).
The end outside of the door is then tied to a nail; by pulling the nail
you pull down the lever _E_, which undoes the bolts and opens the door.
When it is desired to leave the door locked, after it is closed, push the
nail into the latch-string hole so that only the head will be visible from
the outside. When the nail and string are arranged in this manner, a
stranger will see no means of opening the door, and, as there are many
nail-heads in all rough doors, the one to which the latch-string is
attached will not attract the attention of any one who is unacquainted
with the Deming twin bolt.