Before the introduction of the match, the difficulty in obtaining a light at night to see the time made it desirable to have clocks capable of striking the time at will by the operation of a lever or by pulling a cord. In the simplest form of trip repeat mechanism, a lever is arranged to lift the rack hook, allowing the clock to strike the previous hour. In clocks with full repeating action, an additional train of wheels is used to control the speed of the hammer blows. It is similar to an ordinary striking train, and is driven by an additional spring wound by operating the repeating action, which allows the clock to be repeated as often as desired. The repeating mainspring, not visible, is mounted on the inner end of the arbor. On pulling the cord, the arbor rotates, winding the mainspring and moving the segment via the pinion until the segment contacts the snail and prevents further winding. The arbor carries a wheel between the plates fitted with twelve lifting pins on one side for the hours; the number of pins which pass the hour hammer tail on pulling the repeating cord is controlled by the snail. When the repeating cord is released, the mainspring drives the repeating train, delivering a blow for each pin which passes the hammer tail. An arm controls the final resting position of the repeating train. The right-hand end of the arm passes between one pair of pins. The position of the arm is controlled by a quarter-snail. The hammer-lifting wheel carries, in addition to the hour-lifting pins, three longer lifting pins which lift both the hour hammer and an additional hammer striking on a higher-toned bell. If the clock is repeated during the first quarter after an hour, the previous hour is struck and the mechanism is stopped by the arm before any of the quarter-lifting pins can act. When the mechanism is operated during the second quarter, the tip of the arm passes between the innermost pair of pins, allowing the arbor to rotate a little more than in the first quarter, which in turn allows one of the quarter-lifting pins to operate both hammers, thereby indicating the time by a ting-tang double blow. The action for the remaining two quarters is similar, with an additional ting-tang for each. Clock repeating mechanisms have never achieved the standardization found in striking and going trains. Many repeating clocks have additional bells and play a short musical phrase or each quarter. Repeating clocks were first made towards the end of the 17th century. By the 19th century, clocks were rarely fitted with full repeating mechanism.