The Bell That Made Every Hour the Same Length

Before the 1330s, an hour in Milan was not a fixed unit. It was a twelfth of daylight or a twelfth of night, so it stretched long on a June afternoon and shrank to almost nothing in December. Time was measured by the sun's daily arc, not by any constant beat.

That changed with a clock. Around 1336, a mechanical clock was installed in the tower of San Gottardo in Corte, the palace church built for the Visconti rulers of Milan. It had no dial, only a bell, struck once for the first hour after sunset, twice for the second, and so on up to twenty-four, then starting over. The Dominican chronicler Galvano Fiamma recorded it as 'exceedingly necessary for people of all estates,' and the street beside the tower came to be called the Contrada delle Ore, the Street of the Hours.

To ring the right number of strokes without a dial to check against, early clockmakers used a count wheel: a plate with notches spaced further and further apart, one set for each hour, which let the striking mechanism run only as far as the hour required.

The clock's real innovation was invisible: because a mechanism can only beat at a steady rate, its hours had to be equal, all day and all night, all year round. The old, seasonal hour was on its way out. Every watch dial today, with its twelve identical hours, is a descendant of that change.