The term closing bell refers to the ringing of a bell that signals the end of securities trading for the day. The most notable of the closing bells is that of the New York Stock Exchange.
Closing bells have been used on stock exchanges as far back as the 1870s. The purpose of the bell was to ensure an orderly end to a day of trading. The most famous of these bells is that used by the New York Stock Exchange, which rings to close the exchange at 4:00 p.m. Eastern Time.
The first bell on the NYSE was installed in the 1870s and was a Chinese gong. During the move of the exchange in 1903, the gong was replaced by an electronically operated brass bell which was manufactured by the G. S. Edwards Company of Norwalk, Connecticut. The original 1903 design consisted of two bells, one that was 27 inches in diameter and a second one 18 inches in diameter. The large bell was deemed too loud for the exchange and was subsequently removed from service only to be discovered years later.
The NYSE has registered the bell for a trademark and describes its sound as follows:
"...tuned to the pitch D, but with an overtone of D-sharp, struck nine times at a brisk tempo, with the final tone allowed to ring until the sound decays naturally. The rhythmic pattern is eight 16th notes and a quarter note; the total duration, from the striking of the first tone to the end of the decay on the final one, is just over 3 seconds."