CONSTltUCTION OP LOCKS AND KEYS. 9
as can be ascertained, most, if not all, modern locks are based. The Egyptian, the warded, the letter, and the single-tumbler locks, with more, or less alteration, and the exercise of ingenious invention, are, in principle, the foundation on which all modern locks are based.
1st. The letter locks.—These are made as padlocks in considerable numbers; and from the circumstance that no key is required to open them, they are so far convenient. There is one adaptation of the principle of this lock, designed as a ' scutcheon lock,' for securely closing the key-holes of locks for strong doors and iron safes,* but it is too expensive and complicated for general use.
2nd. Locks with fixed wards.—The warded lock, like the ancient Egyptian, has received no improvement, and to prove its utter insecurity, a drawing has been made of a lock and key, with picklocks (Fig. 3), which is copied from a lock taken off the strong room
Fig. 3. WARDED LOCK.
of a London banking-house. A, shows the wards of the lock ; B, the original key, with the cuts in the web exactly corresponding to the wards in the lock; C, is a burglar's instrument, made of tin, having a composition of wax and yellow soap fitted on one side of the bit, so that on its being inserted into the key-hole, a perfect impression of the wards is taken. To make a picklock, it is only necessary to preserve the end of the web which moves the boltj this is accomplished by the instrument D, which is made so as to escape the wards, and will open or shut the lock, as well as the original
* See " Transactions of the Society of Arts," vol. iii. p. 78.