From the end of the thirteenth century clocks were being installed in cathedrals, abbeys and churches around Europe. As early as 1283 a clock is known to have existed in the Dunstable Priory of the Austin Canons. Two surviving clocks from this embryonic period in the history of clocks are those made for Salisbury and Wells Cathedrals. These were made in 1386 and 1389 respectively. The former can still be found in the cathedral itself while the latter is now in the Science Museum in London.
The design of the turret clock changed little over the following three centuries and this particular example has similar characteristics to clocks made for churches in the medieval period. The maker of the clock was Leonard Tenant (died 1646), one of the most prolific makers of church clocks in the first half of the seventeenth century. The clock was installed in Cassiobury Park, a country house near Watford.
The clock is weight-driven and has two separate gear trains mounted side by side. One is the going train which regulates the time and is controlled by a verge escapement with an oscillating foliot with adjustable weights. The other is the striking train which determines the number of blows struck by the hammer on a bell, probably mounted above the clock. Over the years the clock has been modified and restored, but now resembles, in essence, its original conception as a seventeenth century tower clock. The clock is marked with a scallop or cockle shell and is one of a group of five such clocks.