Ocular Window, Keystone
1. ocular window (red)
A rounded English-style window.
2. keystone (blue)
The central block (vousoir) of an arch. Until the keystone is in place, the arch will not support itself.
Keystones, like this one, are often used for ornamentation instead of its original purpose of supporting an arch. There are other ornamental keystones in Carpenters' Hall, like the ones in the moulding over some of the other windows and doorways.
This ocular window can be found on the rear facade of Carpenters' Hall.