Illustrated Architecture Dictionary
Bull's eye / Oculus / Oeil-de-boeuf
1. A figure or ornament of concentric bands (Concentric: Of or denoting circles, arcs, or other shapes that share the same center, the larger often completely surrounding the smaller.)
2. A small circular opening or window
3. A thick knob or boss of glass at the center of a blown glass sheet
4. A thick, circular piece of glass set, as in a roof or ship's deck, to admit light.
5. Oculus or oeil-de-boeuf
Bull's eye corner blocks are found in Federal and Greek Revival styles
Until modern techniques were developed, one way of making window glass was to spin a blob of molten glass at the end of a tool called a pontil. Centrifugal force flattened the glass into a sheet, and when the tool was pulled away it left a characteristic bull's eye mark.
The relatively flat glass on the perimeter of this glass pancake was carefully cut into pieces and sold to the high-brows who could actually afford windows.
What was left, the stuff with the bull's eyes, went into lesser locations, like barns and sheds.
- Old House Web: Bulls Eye Glass (online May 2017)
Examples from Buffalo:
- Butler House Definition #1
- Left illustration above: Forman-Cabana House Definition #2
- Corpus Christi Church Definition #2
- Right illustration above: Coit House Definition #3
- Bemis-Ransom House Terra cotta
- Bemis-Ransom House Another example
- Hull House Federal corner block
- Dun Building Definition #2
- Williams-Butler house Definition #2