The lock represented in the four following figures is also from M. de Réaumur’s chapter on locks in the work referred to. In this lock the tumbler-principle is carried out in a very elaborate manner, for not only is the stump or stud H ([fig. 23]) attached to a very strong spring (best shewn at H, [fig. 22]), which holds it with considerable force in one of the three notches of the principal bolt R S ([fig. 24]); but there is also a second set of notches E E in the gâchette G O ([fig. 21]), and a pin attached to one of the plates of the lock fits into one of these notches, thereby preventing the bolt from being moved until the gâchette is lowered by the revolution of the key; so that in attempting to pick this lock, not only must the spring H be raised so as to release the stud from the notches of the great bolt, but the gâchette must be lowered to disengage the fixed pin from the notches. There is yet a third source of security. Attached to the large bolt are short projecting pins F ([fig. 21]), against which an arm or detent, G F, of the gâchette projects, thus preventing the bolt from being shot back by any pressure applied to its extremity S.
fig. 21. Details of an old French lock.
fig. 22. Another view of the same.
fig. 23. Another view of the same.
fig. 24. The two bolts detached.
There are a few details relating to this remarkable lock, which may as well be introduced here in order to complete the description. The principal bolt can be shot twice, or be double-locked; hence it is furnished with three barbs for the key to act against, and with three notches for the spring-stud. The lower bolt I K can be shot by the horizontal pressure of the button P ([figs. 22], [23]), which is situated on the inner side of the door to which this lock is attached, so that a person inside the room can secure the door against any one on the outside who is not furnished with the proper key, for it must be remarked that the small bolt as well as the large one is acted on by the key. Now supposing the small bolt to be shot or locked, it is kept so by the pressure of the coiled spring Q ([figs. 21], [22]). But this small bolt is connected with the large one by means of the bent lever O N M ([figs. 21], [24]), which turns on a pin N attached to the main bolt. Now, when both bolts are either fully shot or unshot, the arm O N lies flat against and parallel with the main bolt; but when the large bolt is unshot and the small one not moved, the arms O N, N M, fall into an inclined position, and the arm O N passing a little below the main bolt comes within the range of the web of the key, which in its revolution causes the bent lever to move upon its centre N, thereby restoring O N to its horizontal position, and at the same time causing the arm N M to move from right to left, or in the direction for unshooting the small bolt; the end of this arm thus catches into a mortise V ([figs. 21], [24]) in the small bolt, and immediately unlocks it.