This chime is a set of variations by William Crotch (1775-1847) on the fifth and sixth measures of "I know that my redeemer liveth" from Handel's Messiah. He wrote it in 1794 for a new clock at Cambridge University, where he was a student. It was later adopted by St. Stephen's 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 three notes - G, C, D, and E. These permutations are:
1) E, D, C, G 2) C, E, D, G 2b) C, D, E, C (a "malformed" permutation, lacking G) 3) E, C, D, G 4) G, D, E, Cplayed as three quarter-notes and a dotted half. A different sequence of these permutations are 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.
According to tradition, the tune has words: "O Lord our God/Be thou our guide/That by thy help/No foot may slide."