Instruments · a Light

Two brass maps give the direction to Makkah from anywhere

Two engraved brass world maps came to light in the 1990s, made in Iran and generally dated to the seventeenth century. They look ornamental until you understand what the grid is doing. Makkah sits at the centre, and the curved lines around it are laid out so that a ruler pivoted at that centre reads off both the direction of Makkah and the distance to it for any place marked on the plate, with no calculation at all. David King, the historian who published them, argued that the mathematics behind the grid is much older than the objects themselves and goes back to methods worked out around the eleventh century. A hard problem in spherical trigonometry, compressed into a disc of metal you can hold.

Safavid Iran · published by David King