The Westminster Quarters is the most common name for a melody used by a set of clock bells to strike the hour.

This chime is a set of variations on the fifth and sixth measures of "I know that my redeemer liveth" from Handel's Messiah. It was written in 1793 for a new clock in St Mary the Great, the University Church in Cambridge. There is some doubt over exactly who composed it: Revd Dr Joseph Jowett, Regius Professor of Civil Law, was given the job, but he was probably assisted by either Dr Randall, the Professor of Music, or his brilliant undergraduate pupil, William Crotch.

In the mid-19th century the chime was adopted by the Clock Tower at the Palace of Westminster (where Big Ben hangs), whence its fame spread. It is now possibly the most commonly used chime for striking clocks.

It consists of five different permutations of four pitches - G, C, D, and E. These permutations are:

1)  E, D, C, G
2)  C, E, D, G
2b) C, D, E, C (sometimes C, E, D, C; in either case "malformed", as it lacks G)
3)  E, C, D, G
4)  G, D, E, C

played as three crotchets and a dotted minim. A different sequence of these permutations is played at each quarter-hour: one set at the first quarter, two sets at the half, and so forth, as follows:

First quarter: (1)
Half-hour:     (2) (2b)
Third quarter: (3) (4)  (1)
Full hour:     (2) (2b) (3) (4)

The full hour strike is followed by one strike for the number of the hour (one strike for one o'clock, two strikes for two o'clock, etc.)

In other words, a cycle of five permutations, (1), (2), (2b), (3), (4), repeats twice over the course of an hour. For a clock chiming mechanism, this has the advantage that the mechanism that trips the hammers need only store five sequences (1, 2, 2b, 3, 4) instead of ten. The mechanism then plays two complete sets of five sequences for each complete hour.

According to tradition, the tune has words: "O Lord our God/Be thou our guide/That by thy help/No foot may slide."

External links

• The parish of St Mary the Great with St Michael, Cambridge
• Westminster (Cambridge) Chimes
• The Straight Dope on the Westminster Quarters
• A music theory article on the Westminster Quarters and other clock chimes
• Other chimes; Rochester Quarters