new all’s improvements.

503

and the thin part projecting into the keyhole, to beacted upon by the key as hereafter described. Thekey is formed with two grooves cut on the oppositeside of it by a rotary cutter or other means; thegrooves are large enough to admit the small endsof the key-bolts to slide along them, and are formedwith irregular or wavy bottoms, which differ fromeach other, the greatest depths of the grooves beingat the end of the key, so that when the key isinserted into the keyhole up to its shoulder thekey-bolts shall be pressed outwards from the centre,and the thick ends of the inner pieces of the key-bolts are then made to coincide exactly with thecircumference of the key-ring. In this position theouter pieces of the key-bolts can offer no oppositionto the key-ring, being turned round by means ofthe key; but when the key is withdrawn, the springacting upon the outer pieces presses the inner piecesagainst the shoulder. A “ feather” on the key fitsinto the slot of the key-ring to take the strain offthe ends of the key-bolts when the key-ring is beingturned round, and a pin projecting from the key-ring moves the bolt of the lock. The ring is fixedto the box or case of the lock. When the key-ring has made half a turn, the ends of the key-boltscome exactly opposite to each other; and if the keybe withdrawn from its hole, the spring will pressthe key-bolts against their shoulders in the holesand thrust the outer pieces into the ring, so thatthe key-ring cannot be turned round except by