Much of the ingenuity which has been displayed in locks depends on the employment of multiple bolts, there being all the additional strength which results from the use of two or more bolts instead of simply one. Ordinary doors seldom afford us examples of these double bolts; but they may be frequently seen in cabinets and desks, where two staples fixed to the lid fall into two holes in the lock, and are retained by two bolts. The most remarkable and complicated varieties, however, are those in which the bolts, instead of shooting parallel and nearly together, shoot in wholly different ways; one up, one down, one to the right, one to the left, and so on. It is on safes, strong boxes, and the doors of strong rooms containing valuable treasures, that such locks are usually placed. The mechanism is such that the key acts upon all the bolts at once, through the intervention of levers and springs of various kinds.
[Illustration: fig. 16. Multiple bolts of an old chest-lock.]
The above woodcut represents a very curious specimen of these multiple-bolt locks. It is copied from the great French work; and the ponderous chest to which it is attached is, we are told by Réaumur, “known at Paris by the name of the strong German coffer.” He further says, “nothing is wanting in these coffers on the score of solidity. They are made entirely of iron; or if of wood, they are banded both within and without with iron; and can only be broken open by very great violence. Their locks are almost as large as the top of the coffer, and close with a great number of bolts. The one which we have engraved has twelve fastenings; they have been made with twenty-four, or more.” His next remark on the subject is a sensible one: “Notwithstanding the large size of these locks, and all the apparatus with which they are provided, they correspond but ill with the solidity of the rest of the coffer. If we have given a representation of one, it is chiefly to shew how little confidence one could have in such a lock, and what are its defects, in order that we may avoid them.” It is not difficult, by tracing the action of the several levers, to see how one movement of the key, in the centre of the lid, would act upon all the bolts. In the engraving (fig. 16) _a_, _f_, _h_, _c_, are the four corner bolts; six others, _a d e_, _a d e_, are on the long sides, three on each; and two, _b g_, on the short sides. Every bolt is provided with a spring, of which three or four are shewn at Z Z Z. There is no staple or box to receive each bolt; but all shoot or snap beneath the raised edge E running round the top of the box just within the exterior at A A. The keyhole in the front of the box at D is a deception or mask; the real keyhole is in the middle of the lid concealed by a secret door opened by a spring. When the key has moved the great central bolt, this acts upon the other bolts P Q R S T, &c.; V V are studs which act upon two of the bolts; Y Y are staples confining the great bolt; _k_, _l_, _c_, _p_, _x_, are small levers which transmit the action to the corner bolts; _q_, _r_, _s_, _t_, _n_, are the small levers which render a similar service to the side and end bolts; L L within the chest, and M M on the lid, are contrivances for limiting the movement of the latter; C H, H C are iron straps or bands by which the interior of the chest is strengthened. After all, this is not so much a lock as a series of spring latches.