HISTORICAL DEVELOPMENT. In his paper on Locks and Safes (see bibliography), Mr. Chubb traces. in the following manner. the development of locks. The bolt, or essential part of a lock, was probably developed from the bar or •ross.beam with which early peoples secured their doors. This bar was held in sockets or staples fixed on the door, and was secured by means of a pin dropped through a hole in the staple and bar. From this original bar-fastening four different types of locks were developed by primitive men.
The Egyptian placed the bar on the outside of the door and reached the pin which held it through a hole in the bar itself. In other words, the bar, which was shortened into a bolt. was hollow for a part of the distance. instead of one pin. several pins were used. The fully de veloped Egyptian lock consists of a case, which is nailed to the door. Through the case passes a large wooden bolt. the end of which enters the staple, while the opposite end is left exposed. In the lower part of the bolt is a which has certain round or square boles. When the bolt is pushed home into the staple. these holes come exactly under corresponding little cavities in the case, in each of which is placed an upright wooden pin with a knob, which pre vents its falling too low: these little pins conse quently fall into the holes in the bolt when it is pushed far enough, and the door is locked. In order to unlock it. a bar of wood is passed into the groove in the bolt. and on the bar there are the same number of pins of wood placed upright as there are holes in the bolt and loose pins in the chambers of the ease; and these upright pins are placed so as to corre spond exactly in size and position to the holes: therefore, when the pins reach the holes, they slip into them and push up the loose pins into their respective cavities, and the bolt is then easily pulled hack by means of the bar or key. This form of lock, exactly like that made 4000 years ago. is still used in Egypt. The later Roman lock was based upon it, and it contains the principle of the modern pin-tumbler lock. It is easy to see how, in the simplest form of this lock, while the bolt was still a hollow beam, the key was the human arm and the projections on it were the five fingers of the human band used to press up the pins. In order to reach the beam
from the other side of the door. to insert the key, a hole was made in the door through which to pass the hand.
In another class of locks the pins are lifted from the holes in the bolt—the bolt being still on the outside of the door—by means of a hole in the staple. The hole is horizontal, the pins are square in section and are notched on their sides permitting the key to pass into position before they arc lifted: the key is usually flat with little side projections which engage the pins. The bolt is drawn by hand after the key has dis engaged the pins.
In the third type of primitive lock the bolt is on the inside of the door and the pin which holds it does not need to be concealed. The key is a sickle-shaped piece of iron. which is passed through a bole in the door and pushes up the pin on the inside. Just how these keys were manipulated and how- closely they were is uncertain. They must have been widely used, for they are found in abundance in different parts of Europe, especially France and Germany.
'flee fourth type was used in the Roman pad locks, and is still used in China. The bolt is kept out by the projection of a spring or springs which spread out against the sides of the staple. The springs are merely flexible barbs attache] to the bolt. and the key is a flattish one with prongs at the end to engage the springs. The key is passed through a hole in the door and turned and pulled. This compresses the springs so the bolt can be pushed back by the key.
In the fully developed fixed lock of the Romans the parts are of metal; the bolt is much shortened and is concealed behind an ornamental plate. The pins which hold the bolt vary in shape and are pressed down by a flat spring. The key, which reaches the bolt through a hole in the front plate, has projections or teeth in it cor responding to the pins. The key presses up the pins and frees the bolt, so that it can slide ex actly as in the Egyptian lock, During the Middle Ages very complicated and ingenious locks of various kinds were made. and much artistic taste was expended upon their ornamentation. Steele locks. however, were not adapted to general use, and they were found only on the caskets of the wealthy.