


On the Construction of Locks and Keys by John Chubb

CONSTB0CTION OF LOCKS AND KEYS. 15
number of different combinations which may be made on the six steps of unequal lengths, as in Fig. 6, without altering the length of either step. The height of the shortest step is, however, capable of being reduced twenty times, and each time of being reduced, the 720 combinations may be repeated, therefore 720 x 20 = 14,400 changes. The same process, after reducing the shortest step as much as possible, may be gone through with'each of the other five steps; therefore, 14,400 x 6 = 86,400, which is the number of changes that can be produced on the six steps. If, however, the seventh step, which throws the bolt, be taken into account, the reduction of it, only ten times, would give 86,400 x 10 = 864,000, as the number of changes on locks, with the keys all of one size. Moreover, the drill pins of the locks, and the pipes of the keys, may be easily made of three different sizes, and the number of changes will then be, 864,000 x 3 = 2,592,000, as the whole series of changes, which may be gone through with this key.
In smaller keys, the steps of which are only capable of being reduced ten times, and the bolt step only five times, the number of combinations will be 720 X 10 x 6 X 5 x 3 = 648,000. On the other hand, in larger keys, the steps of which can be reduced thirty times, and the bolt step twenty times, the total number of combinations will be 720 x 30 x 6 x 20 x 3 = 7,776,000.
Chubb's locks, like the others, are made in series, having a separate and different key to each, and a master key for opening any number that may be required. So extensive are the combinations, that it would be quite practicable, to make locks for all the doors of all the houses in London, with a distinct and different key for each lock, and yet that there should be one master key to pass the whole.
A most complete series of locks was constructed, some years ago, by the late Mr. Chubb, for the Westminster Bridewell. It consists of about eleven hundred locks, forming one series, with keys for the master, submaster, and warders. At any time the governor has the power of stopping out the underkeys, and in case of any surreptitious attempt being made to open a lock, and the detector being thrown, none of the underkeys will regulate it, but the governor must be made acquainted with the circumstance, as he alone has the power, with his key, to replace the lock in its original state. These locks, although they have been in constant wear for sixteen years, are still in perfect condition.*
It need scarcely be stated, that Barren's, Bramah's, Chubb's, and most other locks, are adapted for all purposes, from the smallest cabinet, to the largest prison doors, or strong room.
* Vide Appendix, Note C, p. 19.



On the Construction of Locks and Keys by John Chubb